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  • Articles  (128)
  • Nitrogen fixation  (67)
  • Rhizosphere  (66)
  • Springer  (128)
  • Geosciences  (128)
  • 1
    Electronic Resource
    Electronic Resource
    Time-course of nitrogen fixation in two bambara groundnut (Vigna subterranea L. Verdc.) cultivars (1994)
    Springer
    Biology and fertility of soils 18 (1994), S. 231-236 
    Details
    ISSN: 1432-0789
    Keywords: A-value ; Bradyrhizobium ; Genotype ; Growth stage ; 15N ; Nitrogen fixation ; Nodulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract TheA-value method, involving the application of a higher15N rate to a reference non-N2-fixing plant, was used to assess the magnitude of N2 fixation in two bambara groundnut cultivars at four growth stages [vegetative, 0–47 days after planting (DAP); early pod-filling, 47–99 DAP; mid-pod-filling, 99–120 DAP; physiological maturity, 120–148 DAP). The cultivars were Ex-Ada, a bunchy type, and CS-88-11, a slightly spreading type. They were grown on a loamy sand. Uninoculated Ex-Ada and CS-88-11 were used as reference plants to measure the N2 fixed in the inoculated bambara groundnuts. In this greenhouse study, soil was the major source of N in bambara groundnuts during vegetative growth, and during this period it accounted for over 80% of the N accumulaed in the plants. However, N2 fixation became the major source of plant N during reproductive growth. There were significant differences between the two cultivars in the ability to fix N2, and at physiological maturity, almost 75% of the N in CS-88-11 was derived from the atmosphere compared to 55% in Ex-Ada. Also, the total N fixed in CS-88-11 at physiological maturity was almost double that in Ex-Ada. Our data indicate that the higher N2 fixation in CS-88-11 was due to two factors, a higher intensity of N2 fixation and a longer active period of N2 fixation. The results also suggest that bambara groundnut genotypes could be selected for higher N2 fixation in farining systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00647672
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrification of ammonium in different components of a flooded rice soil system (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 321-326 
    Details
    ISSN: 1432-0789
    Keywords: Nitrification ; Flooded rice soils ; Rhizosphere ; Rice variety ; Crop growth stage ; Organic amendment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrification associated with the various components [subsurface soil from unplanted and planted (rhizosphere) fields, standing water and surface soil from planted and unplanted fields and leaf sheath suspensions] of submerged rice paddies was examined in incubation experiments with solutions inoculated with soil or water samples. Substantial nitrification occurred in all samples, standing water and surface soil samples in particular, during their 40-day incubation with NH 4 + −N. Almost all the NH 4 + −N, disappeared during incubation with standing water, was recovered as NO inf3 sup- −N. This, compared to 70–80% from all soil samples and only 29% from leaf sheath suspensions. Significant loss of nitrogen, especially from leaf sheath suspensions, is probably due to nitrification-denitrification as evidenced by its complete recovery in the presence of N-Serve. Nitrification potential of the soil and water samples varied with the crop growth stage and was more pronounced at tillering and panicle inititation stages than at other stages. Nitrification potential of samples from green-manure-amended plots was distinctly less than that of samples from control and urea-amended plots. Most probable number (MPN) estimates of ammonium-oxidizing bacteria were always higher in surface soil in both planted and unplanted plots at all stages of crop growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335961
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of soil treatment with cereal straw and method of crop establishment on field pea (Pisum sativum L.) N2 fixation (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 87-95 
    Details
    ISSN: 1432-0789
    Keywords: Crop rotation ; Field pea ; Mineral N ; Nitrogen fixation ; immobilisation ; Pisum sativum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of soil incorporation with cereal straw (nil, 2.5, 5 and 10 t straw ha−1) and direct drilling on the proportion and amount of pea N derived from biological N fixation were investigated in three field experiments. Fixed N was determined by15N dilution using barley as a reference plant. The three sites were on acidic, red clay-loams in the cropping zone of southeastern Australia. Seasonal plant available soil N, as determined by the N accumulated in barley, was 31, 56 and 158 kg N ha−1, for the three sites. Incorporated straw reduced soil nitrate at sowing by 10–50 kg N ha−1 (0–30 cm), and 5 or 10 t straw ha−1 reduced barley uptake of N by 10–38 kg N ha−1. However, reducing plant available soil N was generally ineffective for increasing the N fixed by pea. Fixed N increased only at the site with the least plant-available N, and only one-third of the increase could be attributed to lower soil N uptake by pea. There was no evidence that direct drilling pea increased fixed N by decreasing crop uptake of soil N. It is proposed that a lower requirement for soil N by pea as compared to barley, and availability of mineral N beneath the soil layer treated with straw, minimise the effectiveness of straw incorporation for increasing the N fixed by pea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01420226
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of soil treatment with cereal straw and method of crop establishment on field pea (Pisum sativum L.) N2 fixation (1996)
    Springer
    Biology and fertility of soils 24 (1996), S. 87-95 
    Details
    ISSN: 1432-0789
    Keywords: Key words Crop rotation ; Field pea ; Mineral N ; Nitrogen fixation ; immobilisation ; Pisum sativum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of soil incorporation with cereal straw (nil, 2.5, 5 and 10 t straw ha–1) and direct drilling on the proportion and amount of pea N derived from biological N fixation were investigated in three field experiments. Fixed N was determined by 15N dilution using barley as a reference plant. The three sites were on acidic, red clay-loams in the cropping zone of southeastern Australia. Seasonal plant available soil N, as determined by the N accumulated in barley, was 31, 56 and 158 kg N ha–1, for the three sites. Incorporated straw reduced soil nitrate at sowing by 10–50 kg N ha–1 (0–30 cm), and 5 or 10 t straw ha–1 reduced barley uptake of N by 10–38 kg N ha–1. However, reducing plant available soil N was generally ineffective for increasing the N fixed by pea. Fixed N increased only at the site with the least plant-available N, and only one-third of the increase could be attributed to lower soil N uptake by pea. There was no evidence that direct drilling pea increased fixed N by decreasing crop uptake of soil N. It is proposed that a lower requirement for soil N by pea as compared to barley, and availability of mineral N beneath the soil layer treated with straw, minimise the effectiveness of straw incorporation for increasing the N fixed by pea.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01420226
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  • 5
    Electronic Resource
    Electronic Resource
    Estimating microbial biomass N in soils with and without living roots: Limitations of a pre-extraction step (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 314-318 
    Details
    ISSN: 1432-0789
    Keywords: Microbial biomass N ; Fumigation-extraction ; Pre-extraction ; Rhizosphere ; Roots ; Net-closed soil containers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Special net-closed soil containers were used in a pot experiment with low and high plant densities to give soil samples with and without roots. Soils from the containers were analysed either by the fumigation-extraction method or by a modified procedure starting with a pre-extraction and sieving step to remove plant roots from the samples. In the extracts NO 3 - -N, NH 4 + -N, organic N, and total N were measured. Microbial biomass N was calculated from the differences in total N in fumigated and unfumigated soils. Different plant densities had almost no influence on the values of the N compounds using either method. In soils with roots, significantly more organic N (and total N) was found by the fumigation-extraction method compared to soils without roots while no differences were obtained using pre-extractions and sieving. Though the organic N content in pre-extracts from soils with roots was significantly higher than from soils without roots, the NO 3 - -N and NH 4 + -N content was lower. Significant differences in biomass N in soils with and without roots were found only with the fumigation-extraction method. Biomass N levels calculated using the results after pre-extraction and sieving were about 50% lower than levels detected using fumigation-extraction alone. With the use of special net-closed soil containers, not only were soil samples produced with and without roots, but it was also possible to induce a rhizophere in the soils. A comparison of the two methods using these soils clearly demonstrated that the method used has profound influence on the final biomass N results. While higher “biomass” levels were found by fumigation-extraction in soils with roots, because root N becomes extractable after fumigation, the use of a pre-extraction and a sieving step may underestimate the total biomass N content due to the pre-extraction of microbial N (especially from rhizosphere microorganisms) from the sample. Nevertheless, pre-extraction and sieving followed by fumigation-extraction does seem to be the preferable method for biomass N measurement in comparative studies, because in most cases only minor errors will occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334909
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  • 6
    Electronic Resource
    Electronic Resource
    Nitrification and denitrification in the rhizosphere of rice: the detection of processes by a new multi-channel electrode (2000)
    Springer
    Biology and fertility of soils 31 (2000), S. 427-435 
    Details
    ISSN: 1432-0789
    Keywords: Key words Rice ; Nitrification ; Denitrification ; Rhizosphere ; Microelectrode
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  N turnover in flooded rice soils is characterized by a tight coupling between nitrification and denitrification. Nitrification is restricted to the millimetre-thin oxic surface layer while denitrification occurs in the adjacent anoxic soil. However, in planted rice soil O2 released from the rice roots may also support nitrification within the otherwise anoxic bulk soil. To locate root-associated nitrification and denitrification we constructed a new multi-channel microelectrode that measures NH4 +, NO2 –, and NO3 – at the same point. Unfertilized, unplanted rice microcosms developed an oxic-anoxic interface with nitrification taking place above and denitrification below ca. 1 mm depth. In unfertilized microcosms with rice plants, NH4 +, NO2 – and NO3 – could not be detected in the rhizosphere. Assimilation by the rice roots reduced the available N to a level where nitrification and denitrification virtually could not occur. However, a few hours after injecting (NH4)2HPO4 or urea, a high nitrification activity could be detected in the surface layer of planted microcosms and in a depth of 20–30 mm in the rooted soil. O2 concentrations of up to 150 μM were measured at the same depth, indicating O2 release from the rice roots. Nitrification occurred at a distance of 0–2 mm from the surface around individual roots, and denitrification occurred at a distance of 1.5–5.0 mm. Addition of urea to the floodwater of planted rice microcosms stimulated nitrification. Transpiration of the rice plants caused percolation of water resulting in a mass flow of NH4 + towards the roots, thus supporting nitrification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003749900190
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of pH at the root surface of red clover (Trifolium pratense) grown in soils differing in proton buffer capacity (1988)
    Springer
    Biology and fertility of soils 5 (1988), S. 295-298 
    Details
    ISSN: 1432-0789
    Keywords: pH measurement ; Rhizosphere ; SB electrodes ; Proton secretion of roots ; Red clover ; Rhizotrone ; Rhizobium spp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Measurements of pH were made at the root surface of Trifolium pratense, using Sb electrodes. Nodulated plants were grown in rhizotrones on a sandy soil free of carbonate and on a clay soil rich in carbonate. In the sandy soil, pH at the surface of root laterals was about 1 unit lower than in the bulk soil. The lowest pH values were found at the root tips. In the calcareous soil, pH measured at the root surface did not differ from pH in the bulk soil. This soil had a much higher H+ buffer capacity than the sandy soils. It seems likely that H+ ions excreted from the roots grown in the calcareous soil were directly neutralized by soil carbonate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262134
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  • 8
    Electronic Resource
    Electronic Resource
    Nitrogen-fixing stem nodules on Aeschynomene afraspera (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 61-66 
    Details
    ISSN: 1432-0789
    Keywords: Stem nodulation ; Aeschynomene afraspera ; Legume ; Nitrogen fixation ; Acetylene reduction assay (ARA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Aeschynomene afraspera is a wild annual legume growing in periodically waterlogged soils in western Africa. This legume is characterized by a profuse stem nodulation. Nodules are formed on the stem at the emergence of lateral root primordia, called nodulation sites. These sites are irregularly distributed on vertical rows all along the stem and branches. Stem nodules are hemispherically shaped. Their outside is dark green and they contain a red-pigmented central zone. Stem nodules exhibit a high nitrogen-fixing potential. Acetylene reduction assays result in stem nodule activity of 309 μmol C2H4 g−1 dry nodule h−1. Field-grown stem nodulated Aeschynomene accumulated more N (51 g N m−2 in 10 weeks) than the root nodulated one. Because of this nitrogenfixing potential and its ability to grow in waterlogged conditions, A. afraspera could probably be introduced into tropical rice cropping systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280352
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  • 9
    Electronic Resource
    Electronic Resource
    Azospirillum — plant root associations: A review (1989)
    Springer
    Biology and fertility of soils 8 (1989), S. 356-368 
    Details
    ISSN: 1432-0789
    Keywords: Plant-root associations ; Azospirillum spp ; Rhizosphere ; Nitrogen fixation ; Acetylene reduction assay (ARA) ; Phytohormones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Bacteria of the genus Azospirillum are extensively studied for their plant-growth promoting effect following inoculation. Physiological and biochemical studies of these diazotrophic bacteria are now benefiting from recent breakthroughs in the development of genetic tools for Azospirilum. Moreover, the identification and cloning of Azospirillum genes involved in N2 fixation, plant interaction, and phytohormone production have given new life to many research projects on Azospirillum. The finding that Azospirillum genes can complement specific mutations in other intensively studied rhizosphere bacteria like Rhizobia will certainly trigger the exploration of new areas in rhizosphere biology. Therefore a review of the Azospirillum-plant interactions is particularly timely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00263169
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  • 10
    Electronic Resource
    Electronic Resource
    Denitrification in the rhizosphere of plants with inherently different aerenchyma formation: Wheat (Triticum aestivum) and rice (Oryza sativa) (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 215-219 
    Details
    ISSN: 1432-0789
    Keywords: Denitrification ; Air-filled porosity ; Rhizosphere ; Aerenchyma ; Rice ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Denitrification in the rhizosphere of wheat and rice was studied in relation to aerenchyma formation. Seedlings were grown in quartz silt amended with mineral nutrients at given bulk densities and water tensions. In adventitious wheat roots the formation of cortical lacunae was strongly dependent on soil aeration. Growing the wheat plants in dry (−20 kPa) and moist substrate (−2 kPa) established aerenchyma contents of 3% and 15%, respectively. Denitrification was measured after the introduction of equal moisture levels in the substrates of both treatments. The higher aerenchyma content of roots pregrown in the wetter substrate did not counteract denitrification in the rhizosphere which had doubled in this treatment. In contrast to the unspecific lysis of cortical cell walls, the well organized formation of aerenchyma in rice roots was independent of soil aeration. Root porosity averaged 14%. As in wheat, it was not related to denitrification. However, the level of denitrification per mg of root dry matter was about four times lower than that of wheat. The addition of decomposable organic matter (cellulose) to the substrate stimulated aerenchyma formation in rice and considerably increased denitrification. The results suggest that denitrification in the rhizosphere is independent of aerenchyma formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336228
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  • 11
    Electronic Resource
    Electronic Resource
    Chitinolytic and proteolytic activity of streptomycetes isolated from root-free soil, rhizosphere and mycorrhizosphere of pine (Pinus sylvestris L.) (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 268-272 
    Details
    ISSN: 1432-0789
    Keywords: Streptomycetes ; Chitinolytic ; Proteolytic activity ; Soil ; Pine roots ; Rhizosphere ; Pinus sylvestris
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary We tested 75 strains of Streptomyces spp. (25 taken from each environment of soil, rhizosphere, and mycorrhizosphere of pine, Pinus sylvestris L.) and all exhibited chitinolytic activity and hydrolysed gelatine and sodium caseinate in agar media. Enrichment of these media with glucose and NH4NO3 caused induction or stimulation of proteolytic Streptomyces spp. strains (80%) derived from root-free soil; inhibition of this activity was observed in most strains (92%) isolated from the root zone. The post-culture liquids of the rhizosphere strains cultured in the absence of glucose revealed a significantly higher proteolytic activity than those obtained from the root-free soil. The addition of glucose to the medium stimulated proteolytic activity in the post-culture broth of Streptomyces strains derived from soil and the mycorrhizosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336238
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  • 12
    Electronic Resource
    Electronic Resource
    Nitrogen-fixing potential of Acacia mangium and Acacia auriculiformis seedlings inoculated with Bradyrhizobium and Rhizobium spp. (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 261-267 
    Details
    ISSN: 1432-0789
    Keywords: Acacia mangium ; Acacia auriculiformis ; Bradyrhizobium spp. ; Rhizobium spp. ; Nitrogen fixation ; Nodule efficiency ; Tree legumes ; Agroforestry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two Australian Acacia species, A. mangium and A. auriculiformis were inoculated in vitro with eight strains of Bradyrhizobium spp. and two strains of Rhizobium spp. On the two plant species, only Bradyrhizobium spp. strains formed effective N2-fixing nodules. A. mangium, which nodulates effectively with a restricted range of Bradyrhizobium spp. strains, is a specific host compared to A. auriculiformis. A. auriculiformis is assumed to be a promiscuous host because it nodulates effectively with a wide range of Bradyrhizobium spp. strains. Nodule efficiency as expressed by the ratio of N2 fixed to nodule dry weight appeared to be higher in A. auriculiformis (0.44–0.81) than in A. mangium (0.23–0.55).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336237
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  • 13
    Electronic Resource
    Electronic Resource
    Methanotrophic bacteria in the rhizosphere of rice microcosms and their effect on porewater methane concentration and methane emission (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 93-100 
    Details
    ISSN: 1432-0789
    Keywords: Wetland rice ; Rhizosphere ; Gas diffusion probe ; Methane profiles ; Methane oxidation ; Microcosms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract CH4 emission from irrigated rice field is one of the major sources in the global budget of atmoshperic CH4. Rates of CH4 emission depend on both CH4 production in anoxic parts of the soil and on CH4 oxidation at oxic-anoxic interfaces. In the present study we used planted and unplanted rice microcosms and characterized them by numbers of CH4-oxidizing bacteria (MOB), porewater CH4 and O2 concentrations and CH4 fluxes. Plant roots had a stimulating effect on both the number of total soil bacteria and CH4-oxidizing bacteria as determined by fluorescein isothiocyanate fluorescent staining and the most probable number technique, respectively. In the rhizosphere and on the root surface CH4-oxidizing bacteria were enriched during the growth period of tice, while their numbers remained constant in unplanted soils. In the presence of rice plants, the porewater CH4 concentration was significantly lower, with 0.1–0.4mM CH4, than in unplanted microcosms, with 0.5–0.7mM CH4. O2 was detected at depths of up to 16 mm in planted microcosms, whereas it had disappeared at a depth of 2 mm in the unplanted experiments. CH4 oxidation was determined as the difference between the CH4 emission rates under oxic (air) and anoxic (N2) headspace, and by inhibition experiments with C2H2. Flux measurements showed varying oxic emission rates of between 2.5 and 29.0 mmol CH4m-2 day-1. An average of 34% of the anoxically emitted CH4 was oxidized in the planted microcosms, which was surprisingly constant. The rice rhizosphere appeared to be an important oxic-anoxic interface, significantly reducing CH4 emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336586
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  • 14
    Electronic Resource
    Electronic Resource
    Influence of phosphorus or phosphorus-potassium fertilization on biomass and dinitrogen fixation of the stem-nodulating green-manure legume Sesbania rostrata in different marginally productive wetland rice soils (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 107-112 
    Details
    ISSN: 1432-0789
    Keywords: Wetland rice soils ; Nitrogen fixation ; Sesbania rostrata ; PK fertilization ; Soil Mn ; Acetylene reduction assay ; ARA ; Green manure ; N dilution method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The performance of Sesbania rostrata varies widely from site to site. This makes it difficult to predict the N yield and biomass of this plant in marginally productive soils, and to arouse the interest of farmers in green manure technology. Three consecutive pot experiments were conducted in a greenhouse at the International Rice Research Institute (IRRI) to evaluate growth, nodulation, N2 fixation (C2H2 reduction assay and 15N dilution method), and N yield of 6-week-old S. rostrata on 13 physicochemically different wetland rice soils of the Philippines and on three artificial substrates. The performance of S. rostrata on the unfertilized controls was compared with two fertilizer treatments containing either P (100 mg P kg-1 dry soil) or P+K (100 mg P kg-1 and 200 mg K kg-1 dry soil). In the control soils and substrates, the N yield of S. rostrata varied between 20 and 470 mg N per pot, with the N rate from N2 fixation ranging between 0 and 95%. In three of the nutritionally poor soils even Mn toxicity symptoms apparently occurred with S. rostrata. P application alleviated these symptoms and increased the overall N yield considerably, mainly through increased biological N2 fixation. An additional increase in N yield was obtained by the PK treatment. Multiple regression analysis between soil characteristics and the N yield of S. rostrata showed that the original level of P (Olsen-extracted) and Mn in the soil accounted for 73% of the variance in biomass production by S. rostrata among the unfertilized soils and substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336588
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  • 15
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    Electronic Resource
    The role of potassium fertilizer in nodulation and nitrogen fixation of faba bean (Vicia faba L.) plants under drought stress (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 147-150 
    Details
    ISSN: 1432-0789
    Keywords: Faba bean ; Water stress ; Nodulation ; Nitrogen fixation ; Leghaemoglobin ; Invertase ; Protease ; K fertilizer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three-week-old nodulated faba bean plants were subjected to different levels of drought stress (onehalf, one-quarter, or one-eighth field capacity) for 5 weeks. Half the stressed plants were treated with KCl at 10 mg kg-1 soil or 150 mg kg-1 soil at the beginning of the drought stress. Nodulation and nitrogenase activity were significantly decreased by increasing drought stress. Leghaemoglobin and protein contents of nodule cytosol were also severely inhibited by drought sttess. This decline was attributed to the induction of protease activity. However, carbohydrate contents of the nodule cytosol increased significantly. This accumulation was attributed to a sharp decline in invertase activity and low use of sugar by the bacteroids We conclude that harmful effects of water deficits can be alleviated by increasing K+ supplementation.
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    URL: http://dx.doi.org/10.1007/BF00336594
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  • 16
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    Gram-negative bacterial flora on the root surface of wheat (Triticum aestivum) grown under different soil conditions (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 273-281 
    Details
    ISSN: 1432-0789
    Keywords: Key words Wheat ; (Triticum aestivum) ; Rhizosphere ; Soil microflora ; Gram-negative bacteria ; API 20NE ; Flavobacterium spp. ; Cytophaga
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson‘s test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.
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    URL: http://dx.doi.org/10.1007/BF00335955
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  • 17
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    Dynamics of nodulation, nitrogen fixation, nitrogen use and biomass yield over time in pot-grown Leucaena leucocephala (Lam.) de Wit (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 163-168 
    Details
    ISSN: 1432-0789
    Keywords: Leucaena ; Nodulation ; Nitrogen fixation ; Nitrogen use ; 15N ; Time course
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of nodulation, N2-fixation and N use in Leucaena leucocephala cv. K28 over time was investigated in a screenhouse at 4, 8, 12 and 16 months after planting (MAP) using the 15N-labelling method. Leucaena had a consistently increasing pattern of nodulation, dry biomass and nitrogen yield. A sharp rise in nodulation was observed between 12 and 16 MAP, whereas for biomass, N accumulation and N2-fixation, and N2-fixation, an upward surge occurred between 4 and 12 months. Nodulation, N accumulation, N2-fixation and biomass yield all peaked at 16 MAP. Along with the steady increase in N2-fixation throughout the 16-month growth period, the % N derived from the atmosphere rose from 17.9% to 61.5%, 70.1% and 74%, equivalent to 191, 1623, 2395 and 3385 mg N2 fixed plant-1 at 4, 8, 12 and 16 MAP, respectively. Nitrogen assimilation from soil and fertilizer decreased inversely to the increase in symbiotic nitrogen fixation with time.
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    URL: http://dx.doi.org/10.1007/BF00336553
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  • 18
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    Comparison of symbiotic effectiveness of Rhizobium sp. with positive hydrogen-uptake activity compared with negative mutants in relation to nitrogen fixation in mungbean (Vigna radiata L.) (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 270-274 
    Details
    ISSN: 1432-0789
    Keywords: Mungbean ; Vigna radiata ; Nitrogen fixation ; Hydrogen uptake ; Mutation ; Nitrosoguanidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract H2 uptake activity was well distributed in Rhizobium sp. strains isolated from nodules of mung-bean (Vigna radiata L.). Two effective strains, RMP1 und RMP2, exhibiting significantly higher H2 uptake activity were subjected to mutagenesis with nitrosoguanidine. The respective mutation frequencies were 0.18 and 0.19%. Three Hup- mutants each of RMP1 und RMP2 were compared with the wild-type parent strains under pot culture experiments to evaluate the significance of the H2 uptake system in biological N2 fixation. Nodulation capabilities, plant growth characteristics, and the chlorophyll content of the leaves were significantly reduced in the plants treated with Hup- mutants. Nitrogenase activity in Hup- nodules was reduced by 8–41%. Similarly, N accumulation was also reduced singificantly.
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    URL: http://dx.doi.org/10.1007/BF00336089
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  • 19
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    Endomycorrhizae in a newly cultivated acidic meadow: Effects of three years of barley cropping, tillage, lime, and phosphorus on root colonization and soil infectivity (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 160-165 
    Details
    ISSN: 1432-0789
    Keywords: Key words Hordeum vulgare ; Agricultural ecosystem ; Acidic soil ; Soil infectivity ; Endomycorrhizae ; Reduced tillage ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The dynamics of mycorrhizae under disturbance created by crop production is not well understood. A 3-year experiment was undertaken on a nutrient-poor and acidic land that had last been cultivated in the early 1970s. We observed the effects of cropping spring barley (Hordeum vulgare L.) under four P-fertilizer levels and four levels of lime, in a minimum (rototillage), a reduced (chisel), or a conventional tillage system, on the mycorrhizal receptiveness of the host (maximum level of mycorrhizal colonization, as measured at harvest) and soil infectivity most probable number method. The host receptiveness decreased with time, while crop yields and soil infectivity increased simultaneously with time. Liming increased mycorrhizal colonization of barley roots and soil infectivity. P additions decreased root colonization but did not significantly affect the most probable number values. Slightly higher soil infectivity estimates were found under reduced tillage.
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    URL: http://dx.doi.org/10.1007/BF00335928
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  • 20
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    Occurrence of the endophytic diazotrophs Herbaspirillum spp. in roots, stems, and leaves, predominantly of Gramineae (1996)
    Springer
    Biology and fertility of soils 21 (1996), S. 197-200 
    Details
    ISSN: 1432-0789
    Keywords: Herbaspirillum ; Endophytes of Gramineae ; Diazotrophs ; Survival in soil ; Nitrogen fixation ; sugarcane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Since the first description of Herbaspirillum seropedicae in 1986, few data have been published on this diazotroph, possibly due to difficulties in isolating it from soil. In the present study we found that this bacterium seems to be an obligate endophyte which has been isolated from roots, stems, and leaves of a large number of samples of more than 10 different species of the Gramineae family, but only exceptionally from other plants. H. rubrisubalbicans, previously misnamed as “Pseudomonas” rubrisubalbicans, and known as a mild pathogen of sugarcane causing mottled stripe disease, confirms the endophytie habitat of this genus. This species occurs in roots, stems, and leaves of sugarcane and seems to be restricted to this crop. Inoculation of strains from both species into soil in high numbers resulted in a rapid decline in their numbers. In only 30 days the population of Herbaspirillum spp. in soil decreased below detection limits (〈100 cells g-1). When sorghum was planted in this soil, the bacteria reappeared and multiplied within the plant tissues.
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    URL: http://dx.doi.org/10.1007/BF00335935
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  • 21
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    Solubilization of hydroxyapatite by Enterobacter agglomerans and cloned Escherichia coli in culture medium (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 347-352 
    Details
    ISSN: 1432-0789
    Keywords: Key words Phosphate-solubilizing bacteria ; Hydroxyapatite ; Enterobacter agglomerans ; Organic acids ; Phosphate-solubilizing genes ; Rhizosphere ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphate-solubilizing bacteria (PSB) possessing the ability to solubilize insoluble inorganic phosphate were isolated from the rhizosphere soil of wheat. A laboratory study was conducted to investigate the solubilization of phosphate by a known PSB, Enterobacter agglomerans, and by a genetically manipulated bacterium, Escherichia coli. A second laboratory study investigated the release of P from E. agglomerans compared with known acids. For the first laboratory study, a cosmid (pHC79) library of phosphate-solubilizing gene(s) from E. agglomerans chromosome DNA was constructed in E. coli JM109. The clone JM109 (pKKY) showing phosphate solubilization properties was screened on standard medium containing hydroxyapatite (HY). The P concentration significantly increased at 5 and 10 days for JM109 (pKKY) compared with JM109 (pHC79), the control. Although the P concentration increased, there was no significant change in their pHs. Furthermore, an increase in colony-forming units (CFUs) was seen at 5 and 10 days for JM109 (pKKY) but not for JM109 (pHC79). Artificial acidification of the culture medium with HCl, citric acid, oxalic acid, and lactic acid was achieved by shaking for 48h. Acidification with these selected acids solubilized more HY than E. agglomerans growing for 42h at similar pHs. However, a high P concentration was measured in culture medium with E. agglomerans growing for 84h despite similar pHs. Our results suggest that acid production may play an important role in HY solubilization, but is not the sole reason for the increase in P concentration in culture medium.
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    URL: http://dx.doi.org/10.1007/s003740050256
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  • 22
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    Short- and long-term effects of ammonium on photodependent nitrogen fixation in wetland rice fields of Spain (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 353-357 
    Details
    ISSN: 1432-0789
    Keywords: Key words Acetylene reduction assay ; Anabaena sp. ; Ammonium ; Cyanobacteria ; Nitrogen fixation ; Wetland rice fields ; Nitrogenase activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Short- and long-term experiments were conducted in the rice fields of Valencia, Spain, to determine the ecological significance of ammonium on nitrogen fixation. A significant inhibition of nitrogenase activity by ammonium, at concentrations higher than 0.5mM, was observed after 8h of incubation in short-term experiments done with a bloom of the N2-fixing cyanobacterium Anabaena sp. In a second set of short-term experiments for in situ assays of nitrogenase activity in the field, a significant correlation between nitrogenase activity and the number of N2-fixing cyanobacteria in soil was found. No significant inhibition of nitrogenase activity by ammonium at concentrations up to 2mM was observed in these assays after 24h of incubation. This lack of inhibition was probably due to the rapid decrease in ammonium content in the flood water. Only 5% of the ammonium initially added remained in the water 24h later. In the long-term experiments, nitrogenase activity was assayed in plots fertilized with 0, 70 and 140kgNha–1, over the cultivation cycle, for 5 years. A partial inhibition of nitrogenase activity by deep-placed N fertilizers was observed. Differences were only significant in 2 years. Mean results from 5 years only showed significant differences between plots fertilized with 0 and 140kgNha–1. The partial inhibition of nitrogenase activity by ammonium increased over the cultivation cycle. Inhibition was only significant in September, at the end of the cultivation cycle.
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  • 23
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    Phenotypic grouping of Brazilian Bradyrhizobium strains which nodulate soybean (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 407-415 
    Details
    ISSN: 1432-0789
    Keywords: Key wordsBradyrhizobium japonicum ; Bradyrhizobium elkanii ; Genetic variability ; Glycine max ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Several years of research have shown that there is a high genetic and physiological variability among Bradyrhizobium japonicum strains, culminating in a subdivision into two bacterial genotypes, and the description of the new species B. elkanii. In Brazil, large-scale soybean inoculation started in 1960 and today 15 million doses of inoculants are sold per year for an estimated area of 12 million ha. Efforts have been made to find strains able to fix high amounts of N2 under Brazilian soil conditions, but few laboratories cover basic studies on N2 fixation, such as strain classification into the two Bradyrhizobium species. In this study several characteristics of 40 soybean Bradyrhizobium strains, including 4 reference strains of B. japonicum (genotype I) species, 3 of B. elkanii (genotype II) and 1 of a mixed genotype were evaluated. The parameters analysed in vitro were: colony morphology, serological grouping, intrinsic resistance to antibiotics, synthesis of indole acetic acid, expression of hydrogenase activity and growth in a medium enriched with asparagine. In vivo, analyses performed included the nodulation of Rj 4 soybean cultivar Hill and the detection of symptoms caused by rhizobitoxine. These evaluations allowed a phenotypic grouping which positioned most of the strains utilized in Brazilian inoculants and studies, as well as some new strains isolated from the Cerrado region, within the species B. elkanii. However, environmental stresses and adaptation of Bradyrhizobium strains to the soil caused a large physiological and genetic variability in some isolates from the Cerrado soils in relation to the putative parental strain introduced 15 years ago, placing these isolates in an intermediate position between the two Bradyrhizobium species.
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    URL: http://dx.doi.org/10.1007/s003740050333
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  • 24
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    Relative importance of motility and antibiosis in the rhizoplane competence of a biocontrol agent Pseudomonas fluorescens MelRC2Rif (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 416-420 
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    ISSN: 1432-0789
    Keywords: Key wordsPseudomonas fluorescens ; MelRC2Rif ; Motility ; Antibiosis ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Mutants defective in motility or antibiotics production were obtained by Tn5 mutagenesis of a biocontrol agent Pseudomonas fluorescens MelRC2Rif (wt). Tomato or melon seeds were co-inoculated with a Tn5 mutant and wt in a 1:1 ratio and then grown in soil for 10 days. There was no change in ratios of Tn5 mutants defective in antibiosis to wt in the process of rhizoplane colonization, suggesting little contribution of in vitro antibiosis to the rhizoplane competence of P. fluorescens MelRC2Rif. Similar results were also obtained when seeds treated with bacteria were planted in soil artificially infested with fungal pathogens. In contrast, ratios of Tn5 mutants defective in motility to wt significantly decreased, suggesting the contribution of motility to the rhizoplane competence of this bacterium. When a non-motile Tn5 mutant and wt were co-inoculated into soil at a matric potential of pF 2.3 (–20 kPa) and plants were then grown, there was no change in the ratio in rhizoplane colonization, suggesting that motility might have a role in the movement along roots but an insignificant role in the movement from bulk soil towards roots. When they were co-inoculated into 0.2% water agar (WA) instead of soil, a remarkable decline in ratios was detected. Thus it was soil structure that hindered the efficiency of motility. Time course enumeration of rhizoplane colonization of tomatoes grown in WA revealed that motility was an important means of movement towards and/or along roots rather than the multiplication on roots.
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  • 25
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    Nodulation pattern and acetylene reduction (nitrogen fixation) activity of some highland and lowland Acacia species of Ethiopia (1998)
    Springer
    Biology and fertility of soils 27 (1998), S. 60-64 
    Details
    ISSN: 1432-0789
    Keywords: Key words Acacia spp. ; Bradyrhizobium ; Rhizobium ; Nitrogen fixation ; Nitrogen accumulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Endosymbionts from the Ethiopian highland acacia species Acacia abyssinica, A. negrii and A. etbaica, and the lowland species A. nilotica, A. prasinata, A.senegal, A. seyal, A. tortilis and Faidherbia (Acacia) albida were isolated and characterized. Seven tree species were found to be nodulated by species of both Rhizobium and Bradyrhizobium. F. (Acacia) albida and A. senegal were nodulated by only Bradyrhizobium or Rhizobium, respectively. In A. abyssinica, both genera were isolated from the same nodule, whereas in A. nilotica and A. tortilis, both strains were isolated from different nodules of the same plant. The nitrogen fixation (acetylene reduction) activities varied considerably and showed no correlation with the nitrogen content of the plant. Highland species were as effective as lowland plants, thus demonstrating good potential for soil reclamation. The endosymbionts isolated proved rather promiscuous, efficiently nodulating other Acacia spp. and some tropical grain legumes, but did not nodulate temperate legumes.
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  • 26
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    Phosphatase activity in the rhizosphere and its relation to the depletion of soil organic phosphorus (1987)
    Springer
    Biology and fertility of soils 3 (1987), S. 199-204 
    Details
    ISSN: 1432-0789
    Keywords: Phosphatases ; Rhizosphere ; Organic phosphorus ; Allium cepa ; Brassica oleracea ; Triticum aestivum ; Trifolium alexandrinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The distribution of phosphatase activity and of phosphate fractions of the soil in the proximity of roots was studied in order to evaluate the significance of phosphatases in P nutrition of various plants (Brassica oleracea, Allium cepa, Triticum aestivum, Trifolium alexandrinum). A considerable increase in both acid and alkaline phosphatase activity in all the four soil-root interfaces was observed. Maximum distances from the root surface at which activity increases were observed ranged from 2.0 mm to 3.1 mm for acid phosphatase and from 1.2 mm to 1.6 mm for alkaline phosphatase. The increase in phosphatase activity depended upon plant age, plant species and soil type. A significant correlation was noticed between the depletion of organic P and phosphatase activity in the rhizosphere soil of wheat (r = 0.99**) and clover (r = 0.97**). The maximum organic P depletion was 65% in clover and 86% in wheat, which was observed within a distance from the root of 0.8 mm in clover and 1.5 mm in wheat. Both the phosphatases in combination appear to be responsible for the depletion of organic P.
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  • 27
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    Comparing microbial biomass, denitrification enzyme activity, and numbers of nitrifiers in the rhizospheres of Pinus sylvestris, Picea abies and Betula pendula seedlings by microscale methods (1999)
    Springer
    Biology and fertility of soils 30 (1999), S. 14-19 
    Details
    ISSN: 1432-0789
    Keywords: Key words Tree species ; Rhizosphere ; Microbial biomass ; Denitrification enzyme activity ; Autotrophic nitrifiers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Flushes of C and N from fumigation-extraction (FE-C and FE-N, respectively), substrate-induced respiration (SIR), denitrification enzyme activity (DEA) and numbers of NH4 + and NO2 – oxidizers were studied in the rhizospheres of Scots pine (Pinus sylvestris L.), Norway spruce [(Picea abies (L.) Karsten] and silver birch (Betula pendula Roth) seedlings growing in soil from a field afforestation site. The rhizosphere was defined as the soil adhering to the roots when they were carefully separated from the rest of the soil in the pots, termed as "planted bulk soil". Soil in unplanted pots was used as control soil. All seedlings had been grown from seed and had been infected by the natural mycorrhizas of soil. Overall, roots of all tree species tended to increase FE-C, FE-N, SIR and DEA compared to the unplanted soil, and the increase was higher in the rhizosphere than in the planted bulk soil. In the rhizospheres tree species did not differ in their effect on FE-C, FE-N and DEA, but SIR was lowest under spruce. In the planted bulk soils FE-C and SIR were lowest under spruce. The planted bulk soils differed probably because the roots of spruce did not extend as far in the pot as those of pine and birch. The numbers of both NH4 + and NO2 –oxidizers, determined by the most probable number method, were either unaffected or decreased by roots, with the exception of the spruce rhizosphere, where numbers of both were increased.
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  • 28
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    Nitrogen fixation capacity and nodule occupancy by Bradyrhizobium japonicum and B. elkanii strains (1998)
    Springer
    Biology and fertility of soils 27 (1998), S. 393-399 
    Details
    ISSN: 1432-0789
    Keywords: Key words Bradyrhizobium japonicum ; Bradyrhizobium elkanii ; Competitiveness ; Nitrogen fixation ; Soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In a previous study soybean Bradyrhizobium strains, used in Brazilian studies and inoculants over the last 30 years, and strains adapted to the Brazilian Cerrados, a region frequently submitted to environmental and nutritional stresses, were analyzed for 32 morphological and physiological parameters in vivo and in vitro. A cluster analysis allowed the subdivision of these strains into species Bradyrhizobium japonicum, Bradyrhizobium elkanii and a mixed genotype. In this study, the bacteria were analyzed for nodulation, N2 fixation capacity, nodule occupancy and the ability to increase yield. The goal was to find a relationship between the strain groups and the symbiotic performance. Two strains of Brazilian B. japonicum showed higher rates of N2 fixation and nodule efficiency (mg of N mg–1 of nodules) under axenic conditions. These strains also showed greater yield increases in field experiments when compared to B. elkanii strains. However, no differences were detected between B. japonicum and B. elkanii strains when comparing nodule occupancy capacity. The adapted strains belonging to the serogroup B. elkanii SEMIA 566, most clustered in a mixed genotype, were more competitive than the parental strain, and some showed a higher capacity of N2 fixation. Some of the adapted strains, such as S-370 and S-372, have shown similar N2 fixation rates and nodulation competitiveness to two Brazilian strains of B. japonicum. This similarity demonstrates the possibility of enhancing N2 fixing ability, after local adaptation, even within B. elkanii species. Differences in the DNA profiles were also detected between the parental SEMIA 566 and the adapted strains by analyses with the ERIC and REP-PCR techniques. Consequently, genetic, morphological and physiological changes can be a result of adaptation of rhizobia to the soil. This variability can be used to select strains capable of increasing the contribution of N2 fixation to soybean nutrition.
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  • 29
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    The "oxygen paradox" of dinitrogen-fixing bacteria (2000)
    Springer
    Biology and fertility of soils 30 (2000), S. 363-373 
    Details
    ISSN: 1432-0789
    Keywords: Key words Azospirillum species ; Oxygen paradox ; Nitrogen fixation ; Rhizosphere ; Nitrogenase complex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  N2 fixation by aerobic bacteria is a very energy demanding process, requiring efficient oxidative phosphorylation, while O2 is toxic for the nitrogenase complex. N2-fixing bacteria have evolved a variety of strategies to cope with this apparent "O2 paradox". This review compares strategies that azospirilla and other well-known N2-fixing soil bacteria use to overcome this O2 paradox. Attention will be given to the relationships between the natural habitat of these soil bacteria and their prevailing adaptations. In view of this knowledge the following questions will be addressed: are the specific adaptations observed in azospirilla sufficient to allow optimal proliferation and N2 fixation in their natural habitat? Could improving the O2 tolerance of the N2-fixing process contribute to the development of more efficient strains for the inoculation of plants?
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  • 30
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    Microsensor analysis of oxygen and pH in the rice rhizosphere under field and laboratory conditions (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 379-385 
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    ISSN: 1432-0789
    Keywords: Key words Oxygen ; pH ; Rhizosphere ; Microsensor ; Rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  O2 and pH microsensors were used to analyse the microdistribution of O2 and pH inside and outside roots of lowland rice (Oryza sativa L.). The roots of 3-week-old transplants had O2 concentrations of about 20% air saturation at the surface, but due to a high rate of O2 consumption in the rhizosphere, the oxic region only extended about 0.4 mm into the surrounding soil. Also the fine lateral roots created an oxic zone extending about 0.15 mm into the soil. The O2 concentration within the roots approached air saturation close to the base, but only about 40–60% of air saturation in a region about 8 cm below the base where lateral rootlets were present. A shift from air to N2 around the leaves led to a drop of 50% in the O2 concentration after 12 min at a distance of 8.5 cm from the base. Flowering plants did not export O2 to the soil from the majority of their roots, but high microbial activity was present in a very thin biofilm covering the root surface. A brown colour around the thin lateral roots indicated some O2 export from these also during flowering. No oxidized zone was present around the roots at later stages of crop growth. The roots caused only minor minima in pH (〈0.2 pH units) in the rhizosphere as compared to the bulk soil. Illumination of the plants had no effect on rhizosphere pH.
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  • 31
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    Effect of inoculum rate on the performance of chickpea (Cicer arietinum L.) Rhizobium strains in the field (1987)
    Springer
    Biology and fertility of soils 5 (1987), S. 83-87 
    Details
    ISSN: 1432-0789
    Keywords: Inoculation ; Inoculum dose ; Nitrogen fixation ; Chickpea ; Rhizobium spp. ; Cicer arietinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The influence of three inoculum rates on the performance of three chickpea (Cicer arietinum L.) Rhizobium strains was examined in the field on a Mollisol soil. Increasing amounts of inoculum improved the performance of the strains. A normal dose (104 cells per seed) applied at different intervals gave non-significant increases in nodulation, nitrogenase activity (acetylene reduction assay), nitrogen uptake and grain yield. A ten-fold increase in inoculum increased nodule number, shoot dry weight, nitrogenase activity (ARA) and grain yield, but increases over the control were significant only for nodule dry weight and nitrogen uptake by shoot and grain. The highest level of inoculum (100 × normal) significantly increased nodule dry weight, grain yield, total nitrogenase activity (ARA) and nitrogen uptake by shoot and grain. Strain TAL 620 was more effective than the other two. Combined nitrogen (60 kg N ha−1) suppressed nodulation and nitrogenase activity (ARA).
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  • 32
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    Effect of bulk density and soil water tension on denitrification in the rhizosphere of spring wheat (Triticum vulgare (1987)
    Springer
    Biology and fertility of soils 5 (1987), S. 181-187 
    Details
    ISSN: 1432-0789
    Keywords: Denitrification ; Rhizosphere ; Bulk density ; Water tension ; Acetylene inhibition method ; Triticum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Pot experiments were carried out to study the influence of bulk density (D b), soil water tension (pF) and presence of plants (spring wheat) on denitrification in a low-humus Bt-horizon of a udalf. Pots of only 5-cm depth were found to be most suitable for the experiments when using the acetylene inhibition method. Almost homogeneous soil compaction between 1.1 and 1.6g soil cm−3 was achieved by a Proctor tamper. Water tensions were adjusted by means of ceramic plates on which negative pressure was applied. No denitrification was detected in unplanted pots. With planted pots and increasing bulk density denitrification increased more in pots with 14-day-old plants than in pots with 7-day-old plants. With 14-day-old plants N2O emission pot−1 increased steadily from 2 μmol at D b 1.1 to 8 μmol at D b 1.6, when soil moisture was adjusted to pF 1.5, although root growth was impaired by higher bulk density. From an experiment with different bulk densities and water tensions it could be deduced that the air-filled porosity ultimately determined the rate of denitrification. When low water tension was applied for a longer period, water tension had an overriding effect on total denitrification. Denitrification intensity, however, i.e. the amount of N2O g−1 root fresh weight, was highest when low water tension was accompanied by high bulk density. The results suggest that the increase in denitrification intensity at oxygen stress is partly due to higher root exudation.
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    URL: http://dx.doi.org/10.1007/BF00256898
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    Presence and dispersal of infective Frankia in peat and meadow soils in Sweden (1988)
    Springer
    Biology and fertility of soils 6 (1988), S. 39-44 
    Details
    ISSN: 1432-0789
    Keywords: Alnus ; Energy forestry ; Frankia ; Meadow soil ; Nitrogen fixation ; Nodulation ; Peat soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Use of the N2-fixing grey alder, Alnus incana (L.) Moench, as a short-rotation crop for energy production is currently being explored. To evaluate the need for inoculation of alders, the distribution of infective propagules of Frankia in the soil at potential sites for alder plantations was examined. Uninoculated grey alder seedlings were grown in three types of soil. Frequent nodulation was found in a meadow soil which had been free from actinorhizal plants for nearly 60 years, but the alder seedlings failed to nodulate in peat soil from two different bog sites. One of these bogs had been exploited for peat and the surface layer of the peat had been removed, so that the soil samples were taken from deep layers of the peat. At the other site, an area of cultivated peat, there were no infective propagules of Frankia in plots without alders; the infective Frankia was present in plots only where it had been introduced by inoculated alders. There was no detectable air-borne dispersal of Frankia. Instead, water movement might account for the dispersal of Frankia in peat. Although the apparent absence of Frankia in these peat soils necessitates inoculation of alder seedlings before planting out, this makes it possible to introduce and maintain Frankia strains with selected beneficial characteristics, since there is no competition from an indigenous Frankia flora.
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    URL: http://dx.doi.org/10.1007/BF00257918
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    Genetic variability in dinitrogen fixation between cowpea [Vigna unguiculata (L.) Walp] cultivars determined using the nitrogen-15 isotope dilution technique (2000)
    Springer
    Biology and fertility of soils 32 (2000), S. 318-320 
    Details
    ISSN: 1432-0789
    Keywords: Key words Genetic variability ; Vigna unguiculata ; Nitrogen-15 method ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  N fixed in 16 cultivars of cowpea [Vigna unguiculata (L.) Walp] inoculated with effective Bradyrhizobium strains collected from the West African MIRCEN culture collection was measured by 15N isotope dilution technique. In all plant parts, significant differences in the percentage of N derived from the atmosphere (%Ndfa) and the amount of Ndfa occurred between the cultivars. Ndoute variety exhibited the highest %Ndfa (74.33% in shoots; 60.90% in roots) and accumulated more fixed N (960 mg N plant–1 and 38 mg N plant–1 in shoots and roots, respectively). Therefore this cultivar should be selected as the highest N-fixing cowpea cultivar. It also should be used in a breeding programme to contribute to the development of cultivars that could stimulate an intensive use of cowpea in many different cropping systems in Africa with a view to maintaining soil fertility.
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    URL: http://dx.doi.org/10.1007/s003740000254
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    Renodulation and characterization of Rhizobium isolates from cicer milkvetch (Astragalus cicer L.) (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 169-174 
    Details
    ISSN: 1432-0789
    Keywords: Key wordsAstragalus cicer ; Nodulation ; DNA ; Milkvetch ; Nitrogen fixation ; Forage legume ; Rhizobium spp.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In 1993 and 1994, 12 bacterial isolates were isolated from root nodules of cicer milkvetch (Astragalus cicer). In the tests for nodulation of A. cicer by these bacterial isolates, five were found to form hypertrophic structures, while only two formed true nodules. These true nodules were formed in a sterilized soil system. This system might be able to act as a DNA donor to provide residual DNA to other microbes in the soil. The rhizobial isolates were thought to have lost genetic material crucial to nodulation during the isolation process. This hypothesis was supported by an experiment in which isolate B2 was able to nodulate A. cicer in vermiculite culture after being mixed with heat-killed rhizobia, Rhizobium leguminosarum bv. trifolii and R. loti. The nodulation would not occur in vermiculite culture system without the heat-killed rhizobia. Based on the biochemical data, the B2 and 9462L, which formed true nodules with A. cicer, were closely related. The rhizobia type cultures that nodulate A. cicer include Bradyrhizobium japonicum, Rhizobium leguminosarum bv. trifolii, R. leguminosarum bv. viceae, and R. loti. All of these rhizobia were from different cross-inoculation groups. The B2 and 9462L isolates could only nodulate Medicago sativa, Phaseolus vulgaris, and Melilotus officinalis, but not these species within the genus from which they were isolated: Astragalus. The traditional cross-inoculation group concept obviously does not fit well in the classification of rhizobia associated with Astragalus. The rhizobia isolated from A. cicer can be quite different, and the rhizobia able to renodulate A. cicer also quite diverse.
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    URL: http://dx.doi.org/10.1007/s003740050299
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    Impact of nodule damage by Rivellia angulata on N2-fixation, growth, and yield of pigeonpea (Cajanus cajan L. Millsp.) grown in a Vertisol (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 95-100 
    Details
    ISSN: 1432-0789
    Keywords: Nodule damage ; Rivellia angulata ; Nitrogen fixation ; Cajanus cajan ; Pigeonpea ; Vertisol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Damage caused by Rivellia angulata larvae to pigeonpea root nodules at the ICRISAT center in India was greater in the crop grown on Vertisols (up to 86%) compared to that on Alfisols (20%). Attempts to quantify the field effects of nodule damage on growth and yield of pigeonpea in a Vertisol, involving many heavy applications of soil insecticides (aldrin and hexachlorocyclohexane) failed because the insecticides did not control the pest and adversely affected the growth of the pigeonpea and the subsequent crop of sorghum (Sorgorum bicolor L. Moench). The impact of nodule damage on pigeonpea growth, yield and nutrient uptake was successfully studied in greenhouse-grown plants at three N levels. In this pot study, artificial inoculation with Rivellia sp. led to substantial nodule damage (70%). The results of this damage were a significant overall reduction in nodule dry weight (46%), acetylene reduction activity (31%), total leaf area (36%), chlorophyll content of leaves (39%) and shoot dry weight (23%) 68 days after sowing. At maturity, Rivellia sp. infestation caused significant reductions in top dry weight (22%), root and nodule dry weight (27%), seed dry weight (14%), and total N (29%) and P uptake (19%). The problems and prospects of manipulating nodule damage so as to reduce N losses in pigeonpea are discussed.
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    URL: http://dx.doi.org/10.1007/BF00292565
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    Nodulation competition among Bradyrhizobium japonicum strains as influenced by rhizosphere bacteria and iron availability (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 108-112 
    Details
    ISSN: 1432-0789
    Keywords: Bradyrhizobium japonicum ; Glycine max ; Soil inoculation ; Nodulation ; Rhizosphere ; Rhizobacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Bacteria isolated from the root zones of field-grown soybean plants [Glycine max (L.) Merr.] were examined in a series of glasshouse experiments for an ability to affect nodulation competition among three strains of Bradyrhizobium japonicum (USDA 31, USDA 110, and USDA 123). Inocula applied at planting contained competing strains of B. japonicum with or without one of eleven isolates of rhizosphere bacteria. Tap-root nodules were harvested 28 days after planting, and nodule occupancies were determined for the bradyrhizobia strains originally applied. Under conditions of low iron availability, five isolates (four Pseudomonas spp. plus one Serratia sp.) caused significant changes in nodule occupancy relative to the corresponding control which was not inoculated with rhizosphere bacteria. During subsequent glasshouse experiments designed to verify and further characterize these effects, three fluorescent Pseudomonas spp. consistently altered nodulation competition among certain combinations of bradyrhizobia strains when the rooting medium did not contain added iron. This alteration typically reflected enhanced nodulation by USDA 110. Two of these isolates produced similar, although less pronounced, effects when ferric hydroxide was added to the rooting medium. The results suggest that certain rhizosphere bacteria, particularly fluorescent Pseudomonas spp., can affect nodulation competition among strains of R. japonicum. An additional implication is that iron availability may be an important factor modifying interactions involving the soybean plant, B. japonicum, and associated microorganisms in the host rhizosphere.
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    Yield response of spring wheat cultivars (Triticum aestivum and T. turgidum) to inoculation with Azospirillum brasilense under field conditions (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 27-35 
    Details
    ISSN: 1432-0789
    Keywords: Triticum aestivum ; T. turgidum ; Nitrogen fixation ; Field inoculation ; Acetylene reduction assay (ARA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Eight commercial Israeli spring wheat cultivars (six Triticum aestivum and two T. turgidum) grown with 40 and 120 kg N/ha were tested for responses to inoculation with Azospirillum brasilense. At the low level of N fertilization (40 kg/ha), five cultivars showed significant increases in plant dry weight measured at the milky ripe stage; however, by maturation only the cultivar “Miriam” showed a significant increase in grain yield. Two cultivars, which had shown a positive inoculation effect at the earlier stages, had a significant decrease in grain yield. No significant effect of inoculation was found at the high N level. To confirm those results, four wheat (T. aestivum) cultivars were tested separately over 4 years in 4 different locations under varying N levels. Only Miriam showed a consistently positive effect of Azospirillum inoculation on grain yield. Inoculation increased the number of roots per plant on Miriam compared with uninoculated plants. This effect was found at all N levels. Nutrient (N, P and K) accumulation and number of fertile tillers per unit area were also enhanced by Azospirillum, but these parameters were greatly affected by the level of applied N. It is suggested that the positive response of the spring wheat cultivar “Miriam” to Azospirillum inoculation is due to its capacity to escape water stresses at the end of the growth season.
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    URL: http://dx.doi.org/10.1007/BF00280347
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    Nitrogen fixation and balance studies of rice soil (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 15-19 
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    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; N-balance studies ; Azolla ; Blue-green algae ; Chemical N fertilization ; Rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A nitrogen balance study conducted in ceramic pots under net house conditions for four seasons showed that flooded rice soil leaves a positive nitrogen balance (N increase) in soil after rice cropping in both fertilized and unfertilized soil. Recovery of nitrogen from rice soil was more than its input in unfertilized soil, but it was reverse in fertilized soil. Incorporation of Azolla or BGA twice as basal and 20 days after transplanting (DAT) alone or in combination showed higher nitrogen balance and N2-fixation (N gain) in soil than in that where it was applied once either as basal or 20 DAT. Planted soil showed more N2-fixation than that of fallow rice, and flooded soil fixed more nitrogen in comparison to non-flooded soil in light but less in dark. Soil exposed to light fixed more nitrogen than that of unexposed soil in both flooded and non-flooded conditions.
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    Stimulation of root exudation of rice seedlings by Azospirillum strains: carbon budget under gnotobiotic conditions (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 9-14 
    Details
    ISSN: 1432-0789
    Keywords: Rhizosphere ; Nitrogen fixation ; Root exudates ; Soil bacteria ; Carbon budget ; Rice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The association of rice seedlings (cv. Delta) with different strains of Azospirillum was studied under monoxenic conditions in the dark. Axenic 3-day-old seedlings were obtained on a C- and N-free medium and inoculated with 6 · 107 bacteria per plant in a closed vial. Seven days later, different components of a carbon budget were evaluated on them and on sterile controls: respired CO2, carbon of shoot and roots, bacterial and soluble carbon in the medium. Two strains (A. lipoferum 4B and A. brasilense A95) isolated from the rhizosphere of rice caused an increase in exudation, + 36% and + 17% respectively compared with sterile control. Shoot carbon incorporation and respiration were reduced by inoculation. A third strain (A. brasilense R07) caused no significant change in exudation. A. lipoferum B7C isolated from maize did not stimulate rice exudation either. We further investigated a possible effect of nitrogen fixation on this phenomenon: inhibition of nitrogen fixation by 10% C2H2 did not modify the extent of C exudation by rice associated with A. lipoferum 4B or with the non-motile A. lipoferum 4T.
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    Nitrogenase activity and nitrogen-fixing bacteria associated with the roots ofAtriplex spp. growing in saline sodic soils of Pakistan (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 315-320 
    Details
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Atriplex spp. ; Root-associated diazotrops ; Acetylene reduction assy (ARA) ; Saline sodic soils ; Enterobacter agglomerans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary TwoAtriplex spp. growing in low-fertility saline sodic soils were assayed for root-associated nitrogenase activity. The excised washed and unwashed root of the two species.A. lentiformis andA. amnicola, showed high root-associated nitrogenase activity. Acetylene-reducing activity seemed to be directly influenced by moisture. The highest number of diazotrophs, enumerated using a most probable number technique was observed on the root surface. Most of the isolated diazotrophs were identified asEnterobacter agglomerans. Root-associated nitrogenase activity inAtriplex spp. may explain the high protein and biomass content of these plants growing in low-fertility saline sodic soils.
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    URL: http://dx.doi.org/10.1007/BF00634108
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    A comparison of microbial-feeding nematodes and protozoa in the rhizosphere of different plants (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 83-88 
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    ISSN: 1432-0789
    Keywords: Nematodes ; Protozoa ; Rhizosphere ; Nutrient cycling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The biomass of microbial-feeding nematodes and protozoa was measured in the rhizospheres of peas, barley, grass and turnips grown for 10 weeks in pots containing a clay-loam soil; in the rhizospheres of peas and barley grown for 3 weeks in a sandy soil; and in the rhizosphere of barley grown for 11 weeks in an unfertilised and a fertilised clay-loam soil. The nematode biomass was consistently larger in the rhizosphere of all plants in both soils than in the bulk soil, but the protozoa biomass showed a rhizosphere effect only under pea and fertilised barley. The biomass of nematodes in the rhizosphere (1.2–22.3 μg dry weight g-1 dry soil) was greater than the biomass of protozoa (0.1–3.2 μg g-1), and greater under pea〉barley〉grass〉turnip. It is suggested that nematodes are more able to exploit low bacterial densities than protozoa and that they initially migrate into the rhizosphere from the bulk soil. In samples of potato rhizosphere from field-grown plants, the nematode biomass was also greater than the active and total protozoan biomass. It is argued that in the rhizosphere the biomass of microbially feeding nematodes exceeds that of protozoa and that nematodes are more important in terms of nutrient cycling.
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    Short-term measurements of uptake of nitrogen fixed in the rhizospheres of sorghum (Sorghum bicolor) and millet (Pennisetum americanum) (1988)
    Springer
    Biology and fertility of soils 7 (1988), S. 11-15 
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    ISSN: 1432-0789
    Keywords: 15N ; N2 fixation ; Rhizosphere ; Sorghum bicolor ; Pennisetum americanum ; Acetylene reduction assay (ARA)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In a series of short-term experiments root systems of young sorghum and millet plants inoculated with N2-fixing bacteria were exposed to 15N2-enriched atmospheres for 72 h. The plants were grown in a normal atmosphere for up to 22 days after the end of the exposure to allow them to take up the fixed N2. Environmental conditions and genotypes of sorghum and millet were selected to maximise N2-fixation in the rhizosphere. Detectable amounts of fixed N (〉 16 μg/plant) were rapidly incorporated into sorghum plants grown in a sand/farmyard manure medium, but measurable fixation was found on only one occasion in plants grown in soil. N2 fixation was detectable in some experiments with soil-grown millet plants but the amounts were small (2–4 μg/plant) and represented less than 1 % of plant N accumulated over the same period. In many cases there was no detectable 15N2 incorporation despite measurable increases in ethylene concentration found during an acetylene reduction assay.
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    The microarthropod fauna associated with a deep rooted legume, Prosopis glandulosa, in the Chihuahuan Desert (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 330-335 
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    ISSN: 1432-0789
    Keywords: Prosopis glandulosa ; Rhizosphere ; Mites ; Collembolans ; Chihuahuan Desert
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The rhizosphere microarthropod fauna of a woody, deep-rooted legume, Prosopis glandulosa, was sampled at four sites in the northern Chihuahuan Desert and compared with the rhizosphere microarthropod fauna of a co-dominant shrub, Larrea tridentata. Prostigmatid mites (Speleorchestes sp.,Neognathus sp., Rhagidia sp., Tydaeolus sp., Steneotarsonemus sp., Tarsonemus sp., Nanorchestes sp., Gordialycus sp.), the cryptostigmatid mites (Bankisonoma ovata and Passalozetes neomexicanus), the mesostigmatid (Protogamasellus mica), and the collembolan (Brachystomella arida) characterized the fauna at depths greater than 1 m. Microarthropods were recovered from soils at a depth of 13 m at the edge of a dry lake and at depths of 7 m in a dry wash which were pre-European man P. glandulosa habitats. In habitats where P. glandulosa is a recent invader, root depth and microarthropods were less than 3 m. In most habitats, population densites of microarthropods at depths 0.5 m were more than 100 times those at depths ≫ 0.5 m. Population densities of microarthropods associated with P. glandulosa growing at the edge of a dry wash were not significantly smaller at 0.5−1.0 m depth than at 0−0.5 m. The deep-rhizosphere microarthropod fauna is a reduced subset of the fauna of surficial soils, suggesting that this fauna plays a role in decomposition and mineralization processes functionally similar to that of microarthropods in surficial soils.
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    Distribution of microbial biomass across the rhizosphere of barley (Hordeum vulgare L.) in soils (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 341-345 
    Details
    ISSN: 1432-0789
    Keywords: ATP content ; Bulk soil ; CO2 production ; Mineral N ; Nitrification inhibitor ; Rhizosphere ; Sewage sludge ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The microbial activity at the soil-root interface (rhizosphere) of barley was examined using a rhizobox system. In this system, the soil was placed in several compartments separated from each other by a 500-mesh nylon cloth. Plants were grown in the central compartment and after a 2-month growing period the roots were still confined to this compartment. The soil from each compartment was then analyzed for ATP, NO3 /−, total N, total C and CO2 production. The increase in ATP concentration was found in a range of 4 mm around the roots. The ATP content and CO2 production across the rhizosphere were correlated in all the soils used, but changes in NO3 − were not correlated with ATP changes. The range of NO3 − change was wider than that of the ATP change, indicating that NO3 − production is not influenced by the biological activity in the rhizosphere.
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    Gram-positive bacterial flora on the root surface of wheat (Triticum aestivum L.) grown under different soil conditions (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 121-125 
    Details
    ISSN: 1432-0789
    Keywords: Key words Wheat ; Rhizosphere ; Soil Microflora ; Gram-positive Bacteria ; Coryneform Bacteria ; Arthrobacter spp. ; Mol% G+C ; Diaminopimelic acid ; DAP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 108 Gram-positive bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into four groups based on morphological and physiological characteristics, but most appeared to be coryneform. The taxonomic position of the various groups was verified by the guanine+cytosine DNA contents of the strains. In general, the ranges of these values agreed with those described for the respective taxonomic positions in the literature, with a few exceptions. With soil improvement the distribution of the various groups on the root surface changed, with the coryneform group becoming dominant. This group was further divided into five subgroups, according to cell wall components, cellulose-decomposition, and morphological characteristics, and were identified to genus level. The distribution of these subgroups on the root surface of wheat did not alter with soil improvement. The genus Arthrobacter, the dominant subgroup, predominated in every plot.
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    Azospirillum spp. participation in dry matter partitioning in grasses at the whole plant level (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 435-440 
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    ISSN: 1432-0789
    Keywords: Key wordsAzospirillum spp. ; Crop plants ; Plant growth-promoting rhizobacteria ; Plant inoculation ; Rhizosphere ; Shoot-to-root ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Plant growth-promoting rhizobacteria, particularly those from the genus Azospirillum spp., may affect root functions such as growth and nutrient/water uptake, which in turn may affect shoot growth. Calculations based on data from literature on shoot and root mass of crop grasses (79 plant/bacteria associations were analyzed) revealed that inoculation with Azospirillum spp. increased the shoot-to-root (S/R) ratio in about half of reported cases and decreased the S/R ratio in the other half. In 11 of 35 cases, the S/R ratio increased when the shoot mass increased more than the root mass. In 23 of 35 cases, the root mass did not increase, yet the S/R ratio still increased. Thus, the increase in the S/R ratio indicated that shoot growth responds to inoculation more than root growth. A decrease in the S/R ratio occurred when (a) root growth dominated shoot growth even though both increased (16 of 36 cases), or (b) root growth either increased or remained unchanged, and shoot growth was either unaffected or even decreased (19 of 36 cases). This analysis suggests that: (a) Azospirillum spp. participates in the partitioning of dry matter (both carbon compounds and minerals) at the whole plant level by affecting root functions, and (b) the bacteria affect crop grass through multiple mechanisms operating during plant development.
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    Gram-positive bacterial flora on the root surface of wheat (Triticum aestivum L.) grown under different soil conditions (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 121-125 
    Details
    ISSN: 1432-0789
    Keywords: Wheat ; Rhizosphere ; Soil Microflora ; Gram-positive Bacteria ; Coryneform Bacteria ; Arthrobacter spp. ; Mol% G+C ; Diaminopimelic acid ; DAP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 108 Gram-positive bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into four groups based on morphological and physiological characteristics, but most appeared to be coryneform. The taxonomic position of the various groups was verified by the guanine+cytosine DNA contents of the strains. In general, the ranges of these values agreed with those described for the respective taxonomic positions in the literature, with a few exceptions. With soil improvement the distribution of the various groups on the root surface changed, with the coryneform group becoming dominant. This group was further divided into five subgroups, according to cell wall components, cellulose-decomposition, and morphological characteristics, and were identified to genus level. The distribution of these subgroups on the root surface of wheat did not alter with soil improvement. The genus Arthrobacter, the dominant subgroup, predominated in every plot.
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    Soil protozoa and forest tree growth: non-nutritional effects and interaction with mycorrhizae (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 263-269 
    Details
    ISSN: 1432-0789
    Keywords: Ectomycorrhiza ; Lactarius ; Minearl nutrition ; Picea abies ; Plant growth ; Protozoa ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Mycorrhizal (Lactarius rufus Fr.) and non-mycorrhizal Norway spruce seedlings (Picea abies Karst.) were grown in a sand culture and inoculated with protozoa (naked amoebae and flagellates) extracted from native forest soil or with protozoa grown on agar cultures. A soil suspension from which the protozoa were eliminated by filtration or chloroform fumigation was used as a control. After 19 weeks of growth in a climate chamber at 20–22°C, the seedlings were harvested. Protozoa reduced the number of bacterial colony-forming units extracted from the rhizoplane of both non-mycorrhizal and mycorrhizal seedlings and significantly increased seedling growth. However, concentrations of mineral nutrients in needles were not increased in seedlings with protozoan treatment. It is concluded that the increased growth of seedling was not caused by nutrients released during amoebal grazing on rhizosphere micro-organisms. The protozoa presumably affected plant physiological processes, either directly, via production of phytohormones, or indirectly, via modification of the structure and performance of the rhizosphere microflora and their impact on plant growth. Mycorrhizal colonization significantly increased the abundance of naked amoebae at the rhizoplane. Our observations indicate that protozoa in the rhizosphere interact significantly with mycorrhizae.
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    URL: http://dx.doi.org/10.1007/BF00336088
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    Plant and soil responses to mycorrhizal fungi and rhizobacteria in nodulated or nitrate-fertilized peas (Pisum sativum L.) (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 164-168 
    Details
    ISSN: 1432-0789
    Keywords: Key wordsBacillus ; Glomus ; Mycorrhiza ; Pisum ; sativum ; Plant response ; Rhizosphere ; Root nodule ; Soil aggregation ; Soil pH ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Rhizosphere organisms affect plant development and soil stability. This study was conducted to determine the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus [Glomus mosseae (Nicol. &〉; Gerd.) Gerd. and Trappe] and a rhizobacterium (Bacillus sp.) on nitrate-fertilized or nodulated pea (Pisum sativum L.) plants and on the status of water-stable soil aggregates. The plants were grown in pots in a yellow clay-loam soil, and inoculated with the VAM fungus and the rhizobacterium, with one of the two, or with neither. The Bacillus sp. and G. mosseae did not affect shoot dry mass in nodulated plants. Under N fertilization, the VAM fungus enhanced plant growth, while the rhizobacterium inhibited shoot growth, VAM root colonization, and nodule formation, but enhanced the root:shoot and the seed:shoot ratios. The inhibition of shoot growth and of root colonization appeared to be related. The water stability and pH of the VAM soils were higher than those of the non-VAM soils. The rhizobacterium enhanced the water-stable aggregate status in the non-VAM soils only. Under both N-nutrition regimes, the soils had the greatest proportion of the water-stable aggregates when inoculated with both rhizo-organisms and the lowest when colonized by neither. The two rhizo-organisms affected both plants and soil, and these effects were modified by the source of N input through N2 fixation or fertilization.
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    URL: http://dx.doi.org/10.1007/s003740050225
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    Enhanced dissolution of phosphate rocks in the rhizosphere (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 169-174 
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    ISSN: 1432-0789
    Keywords: Key words Dissolution ; Open leaching ; Organic acids ; Phosphate rocks ; Plant uptake ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Dissolution of two phosphate rocks (PRS) which vary in their chemical reactivity was examined using two soils in the absence (closed-incubation and open-leaching) and presence (thin-layer) of plants. Greater dissolution was obtained in the presence than in the absence of plants. In the absence of plants, open-leaching resulted in higher dissolution than the closed-incubation system. Removal of the dissolved Ca from the zone of PR dissolution is considered to be the main reason for the increased dissolution in the open-leaching columns. In the case of the thin-layer experiment, removal of Ca and P through plant uptake and the supply of protons (H+) through the release of organic acids are considered to be the main reasons for the enhanced dissolution of PRs in the rhizosphere.
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    Dual inoculation with strains of Bradyrhizobium japonicum and Azospirillum brasilense to improve growth and biological nitrogen fixation of soybean (Glycine max L.) (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 317-322 
    Details
    ISSN: 1432-0789
    Keywords: Key words Soybean ; Isotope dilution ; Nitrogen fixation ; Bradyrhizobium japonicum ; Soil sterilization ; 15N ; Azospirillum brasilense ; Bacterial inoculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effects of inoculation with Bradyrhizobium japonicum and Azospirillum brasilense strains on the growth of soybean were evaluated with regard to the estimation of N2 fixation using the 15N isotope dilution technique. Inoculation, in general, increased the dry mass of soybean as well as nitrogen content. Dual inoculation with a mixture of B. japonicum and A. brasilense strains was superior over single inoculation with B. japonicum. Nitrogen fixed (Ndfa) varied according to inoculant and soil conditions. Percentages of nitrogen derived from air (% Ndfa) using a non-nodulating isoline were 72% and 76% for B. japonicum and B. japonicum plus A. brasilense, respectively, in non-sterile soil. A similar but higher trend was recorded in sterilized soil, in which the percentages of N2 fixed were 81% and 86% for single and dual inoculation, respectively. The correlation coefficient between N2 fixed and N uptake (r=0.94) and dry mass (r=0.89) was significant. Application of special bacterial inoculants in agricultural systems of Egypt seems to be a promising technology and could be used for improving soybean growth as well as soil fertility, thus minimizing environmental pollution.
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    URL: http://dx.doi.org/10.1007/s003740050250
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    Influence of long-term conservation tillage on soil and rhizosphere microorganisms (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 81-86 
    Details
    ISSN: 1432-0789
    Keywords: Key words Soil tillage ; Rhizosphere microorganisms ; Cereals ; Nitrogen fixation ; Gaeumanomyces graminis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  In long-term field experiments on sandy loam and loamy sand soils, the influence of conservation and conventional tillage on soil and rhizosphere microorganisms was studied. Conservation tillage stimulated rhizosphere bacteria on winter wheat, winter barley, winter rye and maize in different soil layers. Particularly the populations of Agrobacterium spp. and Pseudomonas spp. were increased. On the sandy loam, N2 fixation and nodulation of pea plants were significantly increased. No influence of different soil tillage was determined on the colonization of the rhizosphere by mycorrhiza and saprophytic fungi. Stubble residues infected with Gaeumanomyces graminis were infectious for a longer time on the soil surface than after incorporation into the soil.
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    Fate of blue-green algae in the food web of flooded rice-field ecosystems (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 141-145 
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    ISSN: 1432-0789
    Keywords: Key words Blue-green algae ; Nitrogen fixation ; Rice ecosystem ; Zooplankton ; Benthos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  As part of an integrated pest management project to study the role blue-green algae (BGA) may play in the food web of rice-field ecosystems, 14C-labelled filamentous and monocellular BGA were used as food for fish, zooplankton and benthic fauna in artificial rice fields in the form of three aquaria. 14C present in the organisms was then traced by liquid scintillation to follow the manner in which the labelled BGA were consumed by different organisms. In this study the grazing rate of fish (mud carp) was compared to that of benthic organisms and zooplankton. It was found that fish consumed the BGA at the fastest rates and in the largest amounts, followed by the benthic species and zooplankton. It was also found that filamentous BGA were consumed in higher amounts than monocellular BGA. The importance of grazing in nutrient recycling is emphasized.
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    Kinetic properties and stability of potato acid phosphatase immobilized on Ca-polygalacturonate (1998)
    Springer
    Biology and fertility of soils 27 (1998), S. 97-103 
    Details
    ISSN: 1432-0789
    Keywords: Key words Potato acid phosphatase ; Ca-Polygalacturonate ; Rhizosphere ; Mucigel ; Michaelis-Menten kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Acid phosphatase from potato was adsorbed and immobilized on a pre-formed network of Ca-polygalacturonate, a substrate which has a composition and morphology similar to the mucigel present at the root-soil interface. The influence of different types of organic buffers on enzyme adsorption and activity was investigated. The highest enzyme activity, for free and adsorbed enzyme, was obtained with Na-maleate buffer at pH 6.0, which was used for all subsequent experiments. The Michaelis-Menten kinetic parameters, Vmax and Km, were determined for free and adsorbed phosphatase. Vmax showed a 60% decrease upon adsorption (2.09±0.30 U/mg, for the soluble form and 0.84±0.15 U/mg, for the adsorbed enzyme), whereas Km increased from 0.49±0.15 mM for the free enzyme to 0.99±0.20 mM for adsorbed phosphatase. Phosphatase adsorption decreased as the concentration of NaCl increased, indicating that the enzyme is bound to the carrier gel through coulombic interactions. Adsorption increased stability of the enzyme as compared with the free enzyme (t 1/2 of the activity was 9.4 days and 5.8 days, respectively), but increased thermal and proteolytic inactivation. The pH/activity profile revealed no change in terms of shape or optimum pH (4.5) upon adsorption of the enzyme. These results indicate that adsorption of acid phosphatase on Ca-polygalacturonate induces changes in the kinetic properties and stability of the enzyme, and the same type of response can be extrapolated from these results for acid phosphatases of the rhizosphere.
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    Diurnal and seasonal patterns of nitrogenase activity of red alder in comparison with white clover in silvopastoral agroforestry systems (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 267-270 
    Details
    ISSN: 1432-0789
    Keywords: Key words Red alder ; White clover ; Nitrogenase activity ; Acetylene reduction assay ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Simultaneous measurements were made to assess the diurnal and seasonal patterns of nitrogenase activity of red alder (Alnus rubra Bong.) and white clover (Trifolium repens L.) growing together in a silvopastoral agroforestry system using the acetylene reduction assay. Diurnal measurements were made in the summer and autumn at 3-h intervals whereas seasonal nitrogenase activity was assessed based on observations made at midday in July, September and January to represent the summer, autumn and winter seasons, respectively. No obvious diurnal patterns of nitrogenase activity were found in either red alder or white clover in summer and no significant variations in nitrogenase activity were observed between day and night. However, in autumn, pronounced diurnal patterns were observed in both species. Significantly higher rates of nitrogenase activity per unit dry weigh (dwt) of nodules were detected at 1500 hours in red alder, whereas, in white clover, significantly higher rates were obtained at 2100 hours. There was no significant correlation between diurnal nitrogenase activity and air temperature, photosynthetically active radiation and soil temperature at 10 cm depth in either red alder or white clover. Seasonal rates of nitrogenase activity showed significantly higher activity in summer, which subsequently decreased in autumn, to reach very low levels in the winter. The rates of nitrogenase activity of white clover were consistently higher than those of red alder both diurnally and seasonally. In the three seasons sampled, the average nitrogenase activity for white clover was 66.42 μmol C2H4 g dwt–1 h–1, which was 3.5 times higher than the 18.67 μmol C2H4 g dwt–1 h–1 obtained for red alder.
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    The number of bacteria in the rhizosphere during plant development: relating colony-forming units to different reference units (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 285-291 
    Details
    ISSN: 1432-0789
    Keywords: Key words Chrysanthemum ; Rhizosphere ; Rhizobacteria ; Root age ; Reference unit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The number of bacteria was determined during the growth of chrysanthemum plants on young (tip) and old (base) root parts. We assessed if the same conclusions could be drawn on the dynamics of bacterial populations during plant development when different reference units were used to express the bacterial counts. The results indicated that the total number of bacteria on the base decreased significantly during plant development, when expressed per root length, per root fresh weight or per root surface. The number of bacteria on the tip only decreased significantly when expressed per root length. Using the unit of dry weight of adhering soil, contradictory results were obtained for both base and tip; in general, the number of bacteria increased significantly during plant development. Thus, different reference units may lead to different conclusions. Root surface seemed to be the best unit to use, but the use of this unit requires time-consuming measurements. Regression analyses indicated that the reference unit "root surface" was highly correlated with root fresh weight (R 2=93%). Thus, once this relation is determined, the less time-consuming unit can be measured in the experimental work. To analyse the data, the colony-forming units should be expressed per root surface. Besides bacterial numbers during plant development, we assessed whether the bacterial populations collected showed different growth rates on agar plates. The growth rates of bacteria from the tip and base and different development stages of the plants showed differences, indicating differences in the metabolic state of the collected populations.
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    Solubilization of inorganic phosphates and growth emergence of wheat as affected by Azotobacter chroococcum mutants (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 301-305 
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    ISSN: 1432-0789
    Keywords: Key words Azotobacter chroococcum ; Inorganic phosphate solubilization ; Indole acetic acid ; Growth emergence ; Wheat ; Phytohormone production ; Rhizosphere ; Phosphate solubilizing bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Phosphate-solubilizing strains of A. chroococcum isolated from the wheat rhizosphere were evaluated for their ability to solubilize tricalcium phosphate (TCP), Mussoorie rock phosphate (MRP) and also for indole-acetic-acid (IAA) production. Strains were selected on the basis of the clearance zone on solid agar media of Pikovskaya and Jensen's media containing TCP, and phosphate solubilization in Jensen's liquid culture medium containing both TCP and MRP. Mutants of the best phosphate-solubilizing (TCP 1.52 μg ml–1 MRP 0.19 μg ml–1), IAA-producing A. chroococum strain P-4, were developed and screened for P solubilization and phytohormone production. Five mutants solubilized more P (in the range of 1.5–1.7 μg/ml–1 of TCP and 0.19–0.22 μg ml–1 of MRP) than the parent strains. In vitro growth emergence studies of three wheat varieties, viz. C-306, WH-542 and HD-2009, showed better performance with phosphate-solubilizing mutants than with the parent strain.
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    Relationships between soil aggregation and mycorrhizae as influenced by soil biota and nitrogen nutrition (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 356-363 
    Details
    ISSN: 1432-0789
    Keywords: Key words Arbuscular mycorrhiza ; Collembola ; Nitrogen fertilization ; Nitrogen fixation ; Soil aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effect of the form of N nutrition on soil stability is an important consideration for the management of sustainable agricultural systems. We grew soybean [Glycine max (L.) Merr.] plants in pot cultures in unsterilized soil, and treated them by (1) inoculating them with Bradyrhizobium japonicum, fertilizing with (2) nitrate or (3) ammonia, or (4) by providing only minimum N amendment for the controls. The soils were sampled at 3-week intervals to determine changes in water-stable soil aggregates (WSA), soil pH, the development of roots, arbuscular mycorrhizal (AM) soil and root colonization, and selected functional groups of soil bacteria. The soil fauna was assayed at the end of the experiment (9 weeks). WSA was correlated positively with root and AM soil mycelium development, but negatively with total bacterial counts. Soil arthropod (Collembola) numbers were negatively correlated with AM hyphal length. Soils of nodulated and ammonia-fertilized plants had the highest levels of WSA and the lowest pH at week 9. Sparse root development in the soils of the N-deficient, control plants indicated that WSA formation was primarily influenced by AM hyphae. The ratio of bacterial counts in the water-stable versus water-unstable soil fractions increased for the first 6 weeks and then declined, while counts of anaerobic bacteria increased with increasing WSA. The numbers of soil invertebrates (nematodes) and protozoans did not correlate with bacterial counts or AM soil-hyphal lengths. Soil pH did not affect mycorrhiza development, but actinomycete counts declined with decreasing soil pH. AM fungi and roots interacted as the factors that affect soil aggregation, regardless of N nutrition.
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    Field evaluation of lentil cultivars inoculated with Rhizobium leguminosarum bv. viciae strains for nitrogen fixation using nitrogen-15 isotope dilution (2000)
    Springer
    Biology and fertility of soils 31 (2000), S. 65-69 
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    ISSN: 1432-0789
    Keywords: Key words Nitrogen-15 isotope dilution ; Legumes ; Lens culinaris ; Rhizobium ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  A 15N isotope dilution technique was applied to quantify the extent of N2 fixation in lentil (Lens culinaris Medik.) cultivars as influenced by Rhizobium leguminosarum bv. viciae strains in a field experiment in Pakistan. The experiment was conducted on a soil with a very small indigenous rhizobial population and where N was a limiting factor for crop production. Significant variations in number of nodules, dry weight of nodules, biomass yield, grain yield, total N yield, proportion of plant N derived from N2 fixation (Pfix) and amount of N derived from the atmosphere (Ndfa) were observed among combined treatments of four rhizobial strains and six lentil varieties. In a field previously labelled with 15N, to which a basal dose of 75 kg P2O5 ha–1 was applied as single super phosphate, Ndfa ranged from 15 to 24 kg N ha–1 when calculated according to rhizobial strain and from 4 to 38 kg N ha–1 when calculated according to lentil variety. Lc 26 was the most effective strain and fixed 243% more N than the indigenous population in the uninoculated control. In treatments with the lentil variety PL-406, Ndfa was 38 kg N ha–1, which was 850% higher than with the lentil variety Precoz/F6-20-1×M-85. Generally, the varieties with greater Pfix produced a higher dry matter yield.
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    Phosphate-solubilizing microorganisms associated with the rhizosphere of mangroves in a semiarid coastal lagoon (2000)
    Springer
    Biology and fertility of soils 30 (2000), S. 460-468 
    Details
    ISSN: 1432-0789
    Keywords: Key words Mangrove ; Bacillus spp. ; Enterobacter spp. ; Inorganic phosphate-solubilizing microorganisms ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The phosphate-solubilizing potential of the rhizosphere microbial community in mangroves was demonstrated when culture media supplemented with insoluble, tribasic calcium phosphate, and incubated with roots of black (Avicennia germinans L.) and white [Laguncularia racemosa (L.) Gaertn.] mangrove became transparent after a few days of incubation. Thirteen phosphate-solubilizing bacterial strains were isolated from the rhizosphere of both species of mangroves: Bacillus amyloliquefaciens, Bacillus licheniformis, Bacillus atrophaeus, Paenibacillus macerans, Vibrio proteolyticus, Xanthobacter agilis, Enterobacter aerogenes, Enterobacter taylorae, Enterobacter asburiae, Kluyvera cryocrescens, Pseudomonas stutzeri, and Chryseomonas luteola. One bacterial isolate could not be identified. The rhizosphere of black mangroves also yielded the fungus Aspergillus niger. The phosphate-solubilizing activity of the isolates was first qualitatively evaluated by the formation of halos (clear zones) around the colonies growing on solid medium containing tribasic calcium phosphate as a sole phosphorus source. Spectrophotometric quantification of phosphate solubilization showed that all bacterial species and A. niger solubilized insoluble phosphate well in a liquid medium, and that V. proteolyticus was the most active solubilizing species among the bacteria. Gas chromatographic analyses of cell-free spent culture medium from the various bacteria demonstrated the presence of 11 identified, and several unidentified, volatile and nonvolatile organic acids. Those most commonly produced by different species were lactic, succinic, isovaleric, isobutyric, and acetic acids. Most of the bacterial species produced more than one organic acid whereas A. niger produced only succinic acid. We propose the production of organic acids by these mangrove rhizosphere microorganisms as a possible mechanism involved in the solubilization of insoluble calcium phosphate.
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    Inoculation of rice plants with the endophytic diazotrophs Herbaspirillum seropedicae and Burkholderia spp. (2000)
    Springer
    Biology and fertility of soils 30 (2000), S. 485-491 
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    ISSN: 1432-0789
    Keywords: Key words Herbaspirillum seropedicae ; Burkholderia spp. ; Nitrogen fixation ; Rice ; Gnotobiotic conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Four experiments were performed under gnotobiotic conditions to select strains of the endophytic diazotrophs Herbaspirillum seropedicae and Burkholderia spp. as inocula of rice plants. Eighty strains of H. seropedicae originally isolated from rice, sorghum and maize plants, were tested in test tube cultures with N-free agar as the substrate. Rice plants showed medium and high increases in their fresh weight in response to inoculation with nineteen strains. These strains were tested again, and six strains were then selected to evaluate their contribution to the N of the plant via biological N2 fixation (BNF) using an agar growth medium containing 5 mg N l–1of 15N-labelled (NH4)2SO4. The contribution of the strains to plant N via BNF varied from 54% when rice plants were inoculated with strain ZAE94, to 31% when strain ZAE67 was used. These results were confirmed in the fourth gnotobiotic experiment, which also included strains of the new N-fixing bacteria belonging to the genus Burkholderia, isolated from rice, as well as a strain of Burkholderia vietnamiensis, isolated from rice rhizosphere. Burkholderia spp. strains showed similar effects to those observed for H. seropedicae strains, while B. vietnamiensis fixed only 19% of plant total N. The best four strains were tested in a pot experiment where pre-germinated, inoculated rice seedlings were grown in soil labelled with 15N. The results confirmed the gnotobiotic experiments, although the levels of N in the rice plants derived from BNF of the selected H. seropedicae and Burkholderia spp. strains were lower. Nevertheless, there was an increase in N content in grains of inoculated plants, and the results showed that the method used for strain selection is very useful and can be applied to other strains of N2-fixing bacteria and plants.
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    Adaptation of green manure legumes to adverse conditions in rice lowlands (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 243-248 
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    ISSN: 1432-0789
    Keywords: Key words Adverse soil conditons ; Aeschynomene ; Green manure ; Lowland rice ; Nitrogen fixation ; Sesbania ; Forming system development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Poor adoption of sustainable pre-rice green manure technology by lowland farmers is frequently associated with unreliable legume performance under adverse environmental conditions such as marginal soils, short photoperiod, and unfavorable hydrology. A series of field and microplot experiments were conducted at the International Rice Research Institute (IRRI) in 1991 and 1992 to screen and evaluate 12 promising flood-tolerant legumes for adaptation (N accumulation and biological N2 fixation) to a range of environmental stresses, frequently encountered in rice lowlands. Legumes belonging to the genera Sesbania and Aeschynomene were grown for 8 weeks at 10×10 cm spacing: (1) in a fertile control soil and in four marginally productive irrigated lowland rice soils (sandy Entisol, P-deficient Inceptisol, acid Ultisol, and saline Mollisol); (2) during short- (11.7 h) and long-day (12.3 h) seasons in a favorable irrigated lowland soil; and (3) in an aerobic soil (drought-prone rain-fed lowland) and a deep-flood-prone lowland soil (1 week seedling submergence). A large variability in N accumulation was observed among legume species and across different environments, ranging from less than 1 to over 70 mg N plant–1. The nitrogen derived from the atmosphere (Ndfa) accounted on average for 82% of total N accumulation. Sesbania virgata was least affected by unfavorable soil conditions but its Ndfa was the lowest among the tested species (less than 60%). Stem nodule formation did not convey a significant advantage to legumes grown under adverse soil conditions. However, flooding reduced N2 fixation less in stem-nodulating than in solely root-nodulating species. Most species drastically reduced N accumulation under short-day conditions. Aeschynomene afraspera and S. speciosa were least affected by photoperiod. The considerable genetic variability in the germplasm screened allows the selection of potentially appropriate legumes to most conditions studied, thus increasing N accumulation in green manures.
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    Soil surface disturbances in cold deserts: effects on nitrogenase activity in cyanobacterial-lichen soil crusts (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 362-367 
    Details
    ISSN: 1432-0789
    Keywords: Cryptobiotic ; Cryptogamic ; Microphytic ; Microbiotic ; Deserts ; Nitrogen fixation ; Nutrient cycling ; Lichens ; Microcoleus vaginatus ; Collema tenax ; Heterocysts ; Acetylene reduction assay ; ARA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cyanobacterial-lichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30–100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cyanobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious implications for nitrogen budgets in these ecosystems.
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    URL: http://dx.doi.org/10.1007/BF00335908
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    Azospirillum spp. participation in dry matter partitioning in grasses at the whole plant level (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 435-440 
    Details
    ISSN: 1432-0789
    Keywords: Azospirillum spp. ; Crop plants ; Plant growth-promoting rhizobacteria ; Plant inoculation ; Rhizosphere ; Shoot-to-root ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Plant growth-promoting rhizobacteria, particularly those from the genus Azospirillum spp., may affect root functions such as growth and nutrient/water uptake, which in turn may affect shoot growth. Calculations based on data from literature on shoot and root mass of crop grasses (79 plant/bacteria associations were analyzed) revealed that inoculation with Azospirillum spp. increased the shoot-to-root (S/R) ratio in about half of reported cases and decreased the S/R ratio in the other half. In 11 of 35 cases, the S/R ratio increased when the shoot mass increased more than the root mass. In 23 of 35 cases, the root mass did not increase, yet the S/R ratio still increased. Thus, the increase in the S/R ratio indicated that shoot growth responds to inoculation more than root growth. A decrease in the S/R ratio occurred when (a) root growth dominated shoot growth even though both increased (16 of 36 cases), or (b) root growth either increased or remained unchanged, and shoot growth was either unaffected or even decreased (19 of 36 cases). This analysis suggests that: (a) Azospirillum spp. participates in the partitioning of dry matter (both carbon compounds and minerals) at the whole plant level by affecting root functions, and (b) the bacteria affect crop grass through multiple mechanisms operating during plant development.
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    URL: http://dx.doi.org/10.1007/BF00335919
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    Soil surface disturbances in cold deserts: effects on nitrogenase activity in cyanobacterial-lichen soil crusts (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 362-367 
    Details
    ISSN: 1432-0789
    Keywords: Key words Cryptobiotic ; Cryptogamic ; Microphytic ; Microbiotic ; Deserts ; Nitrogen fixation ; Nutrient ; cycling ; Lichens ; Microcoleus vaginatus ; Collema tenax ; Heterocysts ; Acetylene reduction assay ; ARA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cyanobacterial-lichen soil crusts can be a dominant source of nitrogen for cold-desert ecosystems. Effects of surface disturbance from footprints, bike and vehicle tracks on the nitrogenase activity in these crusts was investigated. Surface disturbances reduced nitrogenase activity by 30–100%. Crusts dominated by the cyanobacterium Microcoleus vaginatus on sandy soils were the most susceptible to disruption; crusts on gypsiferous soils were the least susceptible. Crusts where the soil lichen Collema tenax was present showed less immediate effects; however, nitrogenase activity still declined over time. Levels of nitrogenase activity reduction were affected by the degree of soil disruption and whether sites were dominated by cyanobacteria with or without heterocysts. Consequently, anthropogenic surface disturbances may have serious implications for nitrogen budgets in these ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050184
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    Methane-oxidizing activities and methanotrophic populations associated with wetland rice plants (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 261-265 
    Details
    ISSN: 1432-0789
    Keywords: Key words Methane ; Wetland rice soils ; Oryza sativa ; Methane oxidation ; Acetylene Propylene oxide ; Methanotrophs ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Acetylene up to 500 μl l–1 did not affect methane formation in anoxic soil up to 12 h, but further incubation for 1 week showed strong inhibition of methanogenesis. To ascertain the extent of the oxidation of methane produced from rice-planted pots, the effect of acetylene on methane emission was studied. Two rice varieties (Toyohatamochi and Yamahikari) were grown in a greenhouse in submerged soil in pots. At about maximum tillering, heading, and grain-forming stages, methane fluxes were measured. Flux measurement was performed for 3 h from 6 pm, then acetylene at 100 μl l–1 was added to some of the pots. At 6 a.m. the following day, methane fluxes were again measured for 3 h. Only at maximum tillering stage of the variety Toyohatamochi was a significant increase (1.4 times) in methane flux caused by acetylene observed, whereas in the other treatments no significant increase in methane fluxes by acetylene could be defected. To ascertain the activity of methane monooxygenase (MMO), propylene oxide (PPO) formation from propylene was measured with excised roots and a basal portion of stems of the rice plants grown on the submerged soil. A level of 0.1–0.2 μmol PPO h–1 plant–1 was recorded. The roots showed the highest PPO formation per gram dry matter, followed by basal stems. Methane oxidation was roughly proportional to PPO formation. Soluble MMO-positive methanotroph populations were measured by plate counts. The number of colony-forming units per gram dry matter was 106–105 in roots, and 104–103 in basal stems. These results indicate the possibility of methane oxidation in association with wetland rice plants.
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    URL: http://dx.doi.org/10.1007/s003740050241
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    Using the spermosphere model technique to describe the dominant nitrogen-fixing microflora associated with wetland rice in two Egyptian soils (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 158-163 
    Details
    ISSN: 1432-0789
    Keywords: Rhizosphere ; N2-fixation ; Wetland rice ; Dominant microflora ; Spermosphere model ; Enterobacter cloacae ; Enterobacter agglomerans ; Citrobacter freundii ; Klebsiella planticola ; Azospirillum lipoferum ; Azospirillum brasilense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary This study is an attempt to describe the dominant N2-fixing microflora associated with the roots of wetland rice. Rice cultivar Giza 171 was grown in a phytotron on two alluvial Egyptian soils for 8 days, a stage when the nitrogenase activity of undisturbed plants reached a level of 245 × 10−6 mol C2H4 h−1 g−1 dry weight of leaf. The roots and rhizosphere soils were then used for counting and isolating dominant diazotrophs. Counts and initial enrichment steps were carried out on a selective medium made of an axenic rice plantlet, the “spermosphere model”, incubated under 1 % acetylene. The counts were very high, exceeding 108 bacteria g−1 dry weight of rhizosphere soil. Enterobacteriaceae were dominant; most isolates were Enterobacter cloacae belonging to different biotypes in the two soils. Enterobacter agglomerans, Citrobacter freundii and Klebsiella planticola were also present as members of the dominant microflora. Azospirillum brasilense and Azospirillum lipoferum were present as well, but less abundant.
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    URL: http://dx.doi.org/10.1007/BF00292575
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    Survival and symbiotic properties of Bradyrhizobium japonicum in the presence of thiram: isolation of fungicide resistant strains (1997)
    Springer
    Biology and fertility of soils 26 (1997), S. 141-145 
    Details
    ISSN: 1432-0789
    Keywords: Key wordsBradyrhizobium japonicum ; Nodulation ; Nitrogen fixation ; Soybean ; Thiram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The fungicide thiram, widely used as a chemical seed protectant, induces a strong inhibition of primary nodulation in the crown zone of soybean roots. The present work reports on the isolation of Bradyrhizobium japonicum strains resistant to thiram, some of which (T3B, A86 and A2) maintained their capacity for nodulation and were still efficient symbionts, but some (A1, C1 and C6) lost the ability to stimulate nodulation. Characterization tests such as growth at different pH, denitrifying ability, salt tolerance, production of siderophores and phosphate solubilization were performed on the resistant strains. Inoculants produced from these strains could be appropriate for use with thiram-treated seeds, without causing a loss of bacteria viability.
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    URL: http://dx.doi.org/10.1007/s003740050357
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    Natural abundance of 15N in sweet potato, pumpkin, sorghum and castor bean: possible input of N2-derived nitrogen in sweet potato (1997)
    Springer
    Biology and fertility of soils 26 (1997), S. 152-154 
    Details
    ISSN: 1432-0789
    Keywords: Key wordsCucurbita moschata ; Ipomoea batatas ; Nitrogen fixation ; δ15N method ; Sorghum bicolor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two combinations of plant species, sweet potato (three cultivars) and pumpkin, and sweet sorghum (three cultivars) and castor bean were grown separately in three plots of alluvial soil from June to September 1996. The shoots (leaves plus stems) of sweet potato and pumpkin, and the whole tops (leaves plus stems and grains) of sweet sorghum and castor bean were harvested twice, once in August and once in September in order to analyze their natural abundance of 15N (δ15N). The δ15N values of two of the varieties of sweet potato harvested in September were significantly lower than those of pumpkin, while δ15N values of sweet potato and pumpkin harvested in August, as well as those of sweet sorghum and castor bean harvested in August and September, did not significantly differ. The lower δ15N values observed in the September-harvested sweet potato may indicate that as much as 40% of the N intake of this species is derived from dinitrogen. This species is known to have a high ability to take up N from undefined sources.
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    URL: http://dx.doi.org/10.1007/s003740050359
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    Nitrification of ammonium in different components of a flooded rice soil system (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 321-326 
    Details
    ISSN: 1432-0789
    Keywords: Key words Nitrification ; Flooded rice soils ; Rhizosphere ; Rice variety ; Crop growth stage ; Organic amendment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrification associated with the various components [subsurface soil from unplanted and planted (rhizosphere) fields, standing water and surface soil from planted and unplanted fields and leaf sheath suspensions] of submerged rice paddies was examined in incubation experiments with solutions inoculated with soil or water samples. Substantial nitrification occurred in all samples, standing water and surface soil samples in particular, during their 40-day incubation with NH4 +-N. Almost all the NH4 +-N, disappeared during incubation with standing water, was recovered as NO3 –-N. This, compared to 70–80% from all soil samples and only 29% from leaf sheath suspensions. Significant loss of nitrogen, especially from leaf sheath suspensions, is probably due to nitrification-denitrification as evidenced by its complete recovery in the presence of N-Serve. Nitrification potential of the soil and water samples varied with the crop growth stage and was more pronounced at tillering and panicle inititation stages than at other stages. Nitrification potential of samples from green-manure-amended plots was distinctly less than that of samples from control and urea-amended plots. Most probable number (MPN) estimates of ammonium-oxidizing bacteria were always higher in surface soil in both planted and unplanted plots at all stages of crop growth.
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    URL: http://dx.doi.org/10.1007/BF00335961
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    Adaptation of green manure legumes to adverse conditions in rice lowlands (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 243-248 
    Details
    ISSN: 1432-0789
    Keywords: Adverse soil conditons ; Aeschynomene ; Green manure ; Lowland rice ; Nitrogen fixation ; Sesbania ; Forming system development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Poor adoption of sustainable pre-rice green manure technology by lowland farmers is frequently associated with unreliable legume performance under adverse environmental conditions such as marginal soils, short photoperiod, and unfavorable hydrology. A series of field and microplot experiments were conducted at the International Rice Research Institute (IRRI) in 1991 and 1992 to screen and evaluate 12 promising flood-tolerant legumes for adaptation (N accumulation and biological N2 fixation) to a range of environmental stresses, frequently encountered in rice lowlands. Legumes belonging to the genera Sesbania and Aeschynomene were grown for 8 weeks at 10×10 cm spacing: (1) in a fertile control soil and in four marginally productive irrigated lowland rice soils (sandy Entisol, P-deficient Inceptisol, acid Ultisol, and saline Mollisol); (2) during short- (11.7h) and long-day (12.3 h) seasons in a favorable irrigated lowland soil; and (3) in an aerobic soil (drought-prone rain-fed lowland) and a deep-flood-prone lowland soil (1 week seedling submergence). A large variability in N accumulation was obsersed among legume species and across different environments, ranging from less than 1 to over 70 mg N plant-1. The nitrogen derived from the atmosphere (Ndfa) accounted on average for 82% of total N accumulation. Sesbania virgata was least affected by unfavorable soil conditions but its Ndfa was the lowest among the tested species (less than 60%). Stem nodule formation did not convey a significant advantage to legumes grown under adverse soil conditions. However, flooding reduced N2 fixation less in stem-nodulating than in solely root-nodulating species. Most species drastically reduced N accumulation under short-day conditions. Aeschynomene afraspera and S. speciosa were least affected by photoperiod. The considerable genetic variability in the germplasm screened allows the selection of potentially appropriate legumes to most conditions studied, thus increasing N accumulation in green manures.
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    Gram-negative bacterial flora on the root surface of wheat (Triticum aestivum) grown under different soil conditions (1996)
    Springer
    Biology and fertility of soils 23 (1996), S. 273-281 
    Details
    ISSN: 1432-0789
    Keywords: Wheat ; Triticum aestivum ; Rhizosphere ; Soil microflora ; Gram-negative bacteria ; API 20 NE ; Flavobacterium spp ; Cytophaga
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract We identified 161 Gram-negative bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into seven groups based on major morphological and physiological properties. Taxonomic allocation of the groups was verified by guanine+cytosine contents of DNA. Except for one group, which may be assumed to include bacteria belonging to the genera Flavobacterium and Cytophaga, the various groups were taxonomically united. The distribution of the groups changed with soil improvement. Pseudomonads predominated in unimproved soil, but Flavobacterium and Cytophaga spp. were predominant in the most improved soil. As all the strains were non-fermentative by Hugh and Leifson's test, API 20NE identification was applied. However, many strains were misidentified by this system, especially in the Flavobacterium and Cytophaga spp. group. For ecological studies, the strains were classified to species level by the API 20 NE system and by the results of a combination of guanine+cytosine (mol%) and isoprenoid quinone data. The pattern of distribution of the bacteria on the root surface of wheat varied at species level within one genus depending on soil conditions.
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    Nitrogen use in maize-grain legume cropping systems in semi-arid Kenya (1995)
    Springer
    Biology and fertility of soils 20 (1995), S. 57-62 
    Details
    ISSN: 1432-0789
    Keywords: Nitrogen use ; Nitrogen fertilizer recovery ; Zea mays ; Phaseolus vulgaris ; Vigna unguiculata ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Locally suitable cultivars of maize, beans, and cowpeas were grown in field experiments for four seasons in semi-arid Kenya. For three seasons, the dry matter production and grain yield of maize and beans were not increased by N fertilizer additions up to 120 kg N ha-1. Fertilizer recoveries measured by 15N isotope dilution techniques were low, less than 20%. Inoculated and uninoculated beans failed to fix N2. By contrast the cowpea derived 50% of its N from fixation, equivalent to 197 kg N ha-1. The N content of the grain generally exceeded 40 kg N ha-1, and the N content of the seeds from the grain legumes were greater than those from the cereals. Large inputs of N fertilizer or N by fixation are required if maize-grain legume cropping system in semiarid Kenya are to be sustained in the long term.
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    URL: http://dx.doi.org/10.1007/BF00307842
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    Antagonistic effect of Pseudomonas spp. on pathogenic fungi and enhancement of growth of green gram (Vigna radiata) (1999)
    Springer
    Biology and fertility of soils 29 (1999), S. 62-68 
    Details
    ISSN: 1432-0789
    Keywords: Key words Pseudomonas spp. ; Vigna radiata ; Rhizosphere ; Antifungal activity ; Dinitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Pseudomonas species were isolated from the rhizosphere of green gram [Vigna radiata (L.) Wilczek] and some of the rhizobacterial isolates were found to have a wide range of antifungal activity inhibiting growth of the phytopathogenic fungi Aspergillus sp., Curvularia sp., Fusarium oxysporum and Rhizoctonia solani in culture. These isolates also showed slight inhibition of the growth of a Bradyrhizobium strain (Vigna) in a spot test which was mainly a result of nutrient competition as culture supernatants of the Pseudomonas isolates did not inhibit the growth of bradyrhizobia but inhibited the growth of fungi. The rhizobacterial isolates produced siderophores in Fe-deficient succinate medium. However, the inhibition of fungal growth by different Pseudomonas isolates in Luria Bertani and King's medium B which were not limiting in Fe3+ ions suggested that, besides siderophores, other antifungal compounds (antibiotics) produced by these rhizobacteria were involved in antagonism. On coinoculation of green gram with Pseudomonas strains MRS13 and MRS16 and Bradyrhizobium sp. (Vigna) strain S24, there was a significant increase in nodule weight, plant dry weight and total plant N as compared to inoculation with Bradyrhizobium strain S24 alone, suggesting that the nodule-promoting effects of Pseudomonas sp. lead to an increase in symbiotic N fixation and plant growth.
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    Effect of low pO2 on colonization of maize roots by a genetically altered Pseudomonas putida [PH6(L1019)] (1997)
    Springer
    Biology and fertility of soils 26 (1997), S. 43-49 
    Details
    ISSN: 1432-0789
    Keywords: Key words Low pO2 ; Rhizosphere ; Pseudomonads ; Competition ; LacZY
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Among the factors which may affect colonization of roots by soil bacteria is that of rhizosphere oxygen partial pressure (pO2). The oxygen concentration in the root zone influences both microbes and roots. Roots exposed to low pO2, as might occur during flooding and waterlogging of the soil, become more leaky and loss of soluble carbon increases. To determine whether periods of low pO2 increased root colonization by a genetically altered pseudomonad we inoculated 3- to 4-week-old maize plants, grown in soil and transferred to a hydroponic system or grown in fritted clay, with Pseudomonas putida PH6(L1019)(lacZY+) following exposure of the roots to air or cylinder N2. Numbers of heterotrophs and the marked pseudomonad were determined by dilution plating. Low pO2 generally increased the numbers of bacteria associated with roots exposed to the treatments in solution or in undisturbed fritted clay rooting medium. Under low pO2 in a hydroponic system, roots of intact maize plants tended also to have higher soluble organic C and hexose (anthrone-detectable sugars) than roots exposed to air. The effect of low pO2 was most pronounced in the fritted clay where low pO2 favored colonization by the marked strain; numbers were 3- to 96-fold greater than those on roots flushed with air but accounted for only 0.06–0.61% of the total population. Roots exposed to low pO2 tended to accumulate more C. Results suggest that in the fritted clay, the pseudomonad was able to exploit the increased C supply and to achieve greater numbers on roots exposed to low pO2, whereas the dilution of carbon released from roots in the hydroponic apparatus did not allow for the same magnitude of increase on roots.
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    URL: http://dx.doi.org/10.1007/s003740050341
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    Effects of marigold (Tagetes sp.) roots on soil microorganisms (1998)
    Springer
    Biology and fertility of soils 27 (1998), S. 149-154 
    Details
    ISSN: 1432-0789
    Keywords: Key words Marigold ; Tagetes ; Rhizosphere ; Nematode suppression ; Bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Marigolds (genus Tagetes) suppress populations of soil endopathogenic nematodes such as Pratylenchus penetrans and Meloidogyne species. Nematode suppression by marigolds is thought to be due to thiophenes, heterocyclic sulfur-containing molecules abundant in this plant. When activated, thiophenes such as α-terthienyl produce oxygen radicals. If marigold roots release such a powerful biocidal agent and it is activated in soil, microbial populations in the marigold rhizosphere should be substantially perturbed. We made various measurements of microbial population size and activity in soils that had been cropped to marigolds (Crackerjack, Creole) in the field and in the greenhouse, and compared these with bare soil and soil cropped to rye (Secale cereale L.). Total extractable microbial biomass (measured by the fumigation extraction method), total bacteria (measured by epifluorescence microscopy on 5-(4,6-dichlorotriazine-2-γl) aminofluorescein-stained preparations), heterotrophic bacteria (measured by plate count on various media), and nitrite-oxidizing bacteria (measured by the most-probable-number method) were not significantly different in any of the treatments. Residues of 14C-labelled rye were mineralized slightly more rapidly in rye-cropped soil than in the other treatments, which were comparable. The rates of die-back of introduced cells of the bacteria Escherichia coli and Rhodococcus TE1 were similar in marigold-cropped and control soils, suggesting that there was not a noteworthy accumulation of biocidal agents in soils cropped to marigolds. We conclude that marigolds do not cause a general depression in the numbers of microorganisms in soils, and that nematode control by this plant may not be due to the release of a biocidal agent into the soil.
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    URL: http://dx.doi.org/10.1007/s003740050413
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    Fallow residue management effects on upland rice in three agroecological zones of West Africa (2000)
    Springer
    Biology and fertility of soils 31 (2000), S. 501-507 
    Details
    ISSN: 1432-0789
    Keywords: Key words Fallow ; Legumes ; Nitrogen fixation ; Oryza sativa ; Côte d'Ivoire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Improving fallow quality in upland rice-fallow rotations in West Africa through the site-specific use of leguminous cover crops has been shown to sustain the productivity of such systems. We studied the effects of a range of residue management practices (removal, burning, mulching and incorporation) on fallow biomass and N accumulation, on weed biomass and yield response of upland rice and on changes in soil physical and chemical characteristics in 2-year field trials conducted in three agroecological zones of Côte d'Ivoire. Across fallow management treatments and agroecological zones, rice yields were on average 20–30% higher in legume than in natural fallow plots. Weed biomass was highest in the savanna zone and lowest in the bimodal forest and tended to be less following a legume fallow. Regardless of the type of fallow vegetation and agroecological zone, biomass removal resulted in the lowest rice yields that varied from 0.5 t ha–1 in the derived savanna zone to 1.5 t ha–1 in the Guinea savanna zone. Burning of the fallow vegetation significantly increased yield over residue removal in the derived savanna (0.27 t ha–1, P〈0.05) and bimodal forest zones (0.27 t ha–1, P〈0.01), but not in the Guinea savanna. In both savanna environments, residue incorporation was superior to the farmers' practice of residue removal and rice yield increases were related to amounts of fallow N returned to the soil (r 2=0.803, P〈0.01). In the forest zone, the farmers' practice of residue burning produced the highest yield (1.43 t ha-1 in the case of legumes) and resulted in the lowest weed biomass (0.02 t ha–1). Regardless of the site, improving the quality of the fallow or of its management had no significant effects on either soil physical or soil chemical characteristics after two fallow cycles. We conclude that incorporation of legume residues is a desirable practice for rice-based fallow rotation systems in savanna environments. No promising residue management alternatives to slash-and-burn were apparent for the forest zone. Determining the possible effects on soil productivity will require longer-term experiments.
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    URL: http://dx.doi.org/10.1007/s003740000199
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    Survival and cell culturability of biocontrol Pseudomonas fluorescens CHA0 in the rhizosphere of cucumber grown in two soils of contrasting fertility status (2000)
    Springer
    Biology and fertility of soils 32 (2000), S. 217-221 
    Details
    ISSN: 1432-0789
    Keywords: Key words  Pseudomonas fluorescens ; Cucumber ; Rhizosphere ; Biocontrol ; Culturability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effect of cucumber roots on survival patterns of the biocontrol soil inoculant Pseudomonas fluorescens CHA0-Rif was assessed for 22 days in two non-sterile soils, using a combination of total immunofluorescence cell counts, Kogure's direct viable counts and colony counts on plates containing rifampicin. In Eschikon soil (high fertility status for cucumber), CHA0-Rif persisted as culturable cells in bulk soil and in the rhizosphere, but colony counts were lower than viable counts and total cell counts inside root tissues. The occurrence of viable but non-culturable (VBNC) cells inside root tissues (5 log cells g–1 root) was unlikely to have resulted from the hydrogen peroxide treatment used to disinfect the root surface, as hydrogen peroxide caused the death of CHA0-Rif cells in vitro. In Siglistorf soil (low fertility status for cucumber), the inoculant was found mostly as non-culturable cells. Colony counts and viable counts of CHA0-Rif were similar, both in bulk soil and inside root tissues, whereas in the rhizosphere viable counts exceeded colony counts at the last two samplings (giving about 7 log VBNC cells g–1). In conclusion, soil type had a significant influence on the occurrence of VBNC cells of CHA0-Rif, although these cells were found in root-associated habitats (i.e. rhizosphere and root tissues) and not in bulk soil.
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    URL: http://dx.doi.org/10.1007/s003740000238
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    Misidentification of soil bacteria by fatty acid methyl ester (FAME) and BIOLOG analyses (2000)
    Springer
    Biology and fertility of soils 32 (2000), S. 256-258 
    Details
    ISSN: 1432-0789
    Keywords: Key words Arthrobacter ; Micrococcus ; Rhizosphere ; Similarity index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Fatty acid methyl ester (FAME) analysis is commonly used by soil scientists as a sole method for identifying soil bacteria. We observed discrepancies with this method for identifying certain species of bacteria. Therefore, we used carbon substrate oxidation patterns (BIOLOG) and some simple physical and chemical tests to determine the extent of these discrepancies. Identification with FAME profiles gave false positives for Arthrobacter globiformis, Micrococcus kristinae, and M. luteus, and identification with BIOLOG patterns gave a false positive identification for A. globiformis. A visual check and Gram stain are recommended when FAME analysis identifies soil isolates as M. kristinae or M. luteus, and an additional spore formation test is recommended when FAME and BIOLOG analyses identify isolates as A. globiformis.
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    URL: http://dx.doi.org/10.1007/s003740000244
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    Production of root-derived material and associated microbial growth in soil at different nutrient levels (1987)
    Springer
    Biology and fertility of soils 5 (1987), S. 126-132 
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    ISSN: 1432-0789
    Keywords: Residual soil 14C ; Microbial biomass ; Root-derived organic matter ; Fluorescent pseudomonads ; Rhizosphere ; Nutrient levels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Maize plants were grown for 42 days in a sandy soil at two different mineral nutrient levels, in an atmosphere containing 14CO2. The 14C and total carbon contents of shoots, roots, soil and soil microbial biomass were measured 28, 35 and 42 days after germination. Relative growth rates of shoots and roots decreased after 35 days at the lower nutrient level, but were relatively constant at the higher nutrient level. In the former treatment, 2% of the total 14C fixed was retained as a residue in soil at all harvests while at the higher nutrient level up to 4% was retained after 42 days. Incorporation of 14C into the soil microbial biomass was close to its maximum after 35 days at the lower nutrient level, but continued to increase at the higher level. Generally a good agreement existed between microbial biomass, 14C contents and numbers of fluorescent pseudomonads in the rhizosphere. Numbers of fluorescent pseudomonads in the rhizosphere were maximal after 35 days at the lower nutrient level and continued to increase at the higher nutrient level. The proportions of the residual 14C in soil, incorporated in the soil microbial biomass, were 28% to 41% at the lower nutrient level and 20%6 – 30% at the higher nutrient level. From the lower nutrient soil 18%6 – 52%6 of the residual soil 14C could be extracted with 0.5 N K2SO4, versus 14%6 – 16% from the higher nutrient soil. Microbial growth in the rhizosphere seemed directly affected by the depletion of mineral nutrients while plant growth and the related production of root-derived materials continued.
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    URL: http://dx.doi.org/10.1007/BF00257647
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    A sensitive method for measuring cyanide and cyanogenic glucosides in sand culture and soil (1987)
    Springer
    Biology and fertility of soils 5 (1987), S. 141-147 
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    ISSN: 1432-0789
    Keywords: Cyanogenic glucosides ; Cyanide ; Root exudates ; Rhizosphere ; Linum usitatissimum ; Pteridium aquilinum ; Linamarase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Sensitive methods for measuring cyanide and cyanogenic glucosides in soil and sand culture have been developed. A microdiffusion technique is described which depends on the enzymic conversion of linamarin and lotaustralin to HCN, its release following acidification and incubation, and its detection in NaOH. Conditions for hydrolysis and HCN recovery have been optimised. The cyanide content of a silt loam soil (under non-cyanogenic wheat) was 5.47 nmol cyanide g−1 air-dried soil whilst that in an organic soil under the cyanogenic bracken, Pteridium aqgilinum, was 12.2 nmol g−1. Exudation of cyanogenic glucosides by linseed, Linum usitatissimum, was measured in plant growth tubes containing sand and a nutrient medium. Sterile plants exuded an average of 6.88 nmol glucosides plant−1 week−1 whilst, in contaminated tubes, the level fell to 4.72 nmol. Analysis of plant roots on each sampling occasion showed that 6.88 nmol was, on average, equivalent to 16.15% of the total root content of cyanogenic glucosides. There was a low but positive correlation between fresh weight of plant roots and the level of exuded glucosides. There was no evidence that plant roots produced free HCN.
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    URL: http://dx.doi.org/10.1007/BF00257649
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    Root activity and carbon metabolism in soils (1988)
    Springer
    Biology and fertility of soils 7 (1988), S. 71-78 
    Details
    ISSN: 1432-0789
    Keywords: Root activity ; Rhizosphere ; C metabolism ; Microbial biomass ; Microbial activity ; Wheat ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two different soils were amended with 14C-labelled plant material and incubated under controlled laboratory conditions for 2 years. Half the samples were cropped with wheat (Triticum aestivum) 10 times in succession. At flowering, the wheat was harvested and the old roots removed from the soil, so that the soil was continuously occupied by predominantly active root systems. The remaining samples were maintained without plants under the same conditions. During the initial stages of high microbial activity, due to decomposition of the labile compounds, the size of the total microbial biomass was comparable for both treatments, and the metabolic quotient (qCO2-C = mg CO2-C·mg−1 Biomass C·h−1) was increased by the plants. During the subsequent low-activity decomposition stages, after the labile compounds had been progressively mineralized, the biomass was multiplied by a factor of 2–4 in the presence of plants compared to the bare soils. Nevertheless, qCO2-C tended to reach similar low values with both treatments. The 14C-labelled biomass was reduced by the presence of roots and qCO2-14C was increased. The significance of these results obtained from a model experiment is discussed in terms of (1) the variation in the substrate originating from the roots and controlled by the plant physiology, (2) nutrient availability for plants and microorganisms, (3) soil biotic capacities and (4) increased microbial turnover rates induced by the roots.
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    URL: http://dx.doi.org/10.1007/BF00260736
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    Nodulation of African yam bean (Sphenostylis stenocarpa) by Bradyrhizobium sp. isolated from Erythrina brucei (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 209-210 
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    ISSN: 1432-0789
    Keywords: Key wordsBradyrhizobium ; Sphenostylis stenocarpa ; Nitrogen fixation ; Soil reclamation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract African yam bean (Sphenostylis stenocarpa), which is widely cultivated in Africa because of its growth capability on marginal soils, was nodulated by an endosymbiont (characterized and designed Bradyrhizobium sp. AUEB20) isolated from the Ethiopian tree Erythrina brucei with the formation of a small number of large, indeterminate N2-fixing nodules. In contrast, 24 other isolates from Ethiopian woody legumes were ineffective. Strain AUEB20 promiscuously nodulated a number of tropical legumes, but none out of five European crop plants tested.
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    URL: http://dx.doi.org/10.1007/s003740050305
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    Diversity, adaptation and activity of the bacterial flora in saline environments (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 211-223 
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    ISSN: 1432-0789
    Keywords: Key words Bacterial flora ; Salt-affected soils ; Salt marshes ; Osmotic adjustment ; Microbial activity ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Saline environments have a natural bacterial flora, which may play a significant role in the economy of these habitats. The natural saline environments (usually containing salinity equivalent to 4–30% NaCl) are aquatic (e.g. salt marshes) or terrestrial (e.g. saline lands). Saline environments include an increasing area of salt-affected cultivated soils throughout the world. These environments contain various ions which may interfere with uptake of water and which may be toxic to a large number of organisms. Saline environments harbour taxonomically diverse bacterial groups, which exhibit modified physiological and structural characteristics under the prevailing saline conditions. The majority of these bacteria can osmoregulate by synthesizing specific compatible organic osmolytes such as glutamine, proline and glycine betaine and a few of them accumulate inorganic solutes such as Na+, K+ and Mg2+. The morphology of the bacteria is usually modified, cells are usually elongated, swollen and showing shrinkage, in addition to changes in the cell and cytoplasmic volume. The chemical composition of membranes may also occasionally be modified, and the synthesis pattern of proteins, lipids, fatty acids and polysaccharides may change with a moderate increase in salinity. However, ultrastructural alterations in cells of halophilic bacteria have not been reported, and profound changes in cellular properties of these bacteria only occur at concentrations above 2MNaCl. Evidence has accumulated that the bacteria are essential elements in the saline environment because of their activity such as degradation of plant remains, nitrogen fixation and production of active metabolites.
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    Variation in nitrogen fixation among populations ofFrankia sp. andCeanothus sp. in actinorhizal association (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 269-274 
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    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Frankia-Ceanothus spp. association ; Acetylene reduction assay (ARA) ; Microsymbiont population ; Nodules ; Actinomycetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wildland shrub improvement is needed for sound range and disturbed land revegetation practice. The possibility of selecting superior N2-fixingFrankia-Ceanothus spp. actinorhizal associations was examined. Greenhouse tests were used to expose various soil-borne microsymbiont andCeanothus sp. population accessions in reciprocal combination. The acetylene reduction rate was used as a measure of N2-fixation capacity. There was no significant interaction between host and microsymbiont regardless of source for all variables measured. The acetylene reduction rate, nodule number and mass, plant biomass, and root: shoot ratio were significantly different among soil sources. The acetylene reduction rate was not significantly different amongCeanothus sp. accessions. Neither was it strongly correlated with other variables. It was concluded that the N2-fixation rate is more a function ofFrankia sp. than the hostCeanothus sp. in actinorhizal associations. It appears possible to select soil sources with superior N2-fixing microsymbiont populations.
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    URL: http://dx.doi.org/10.1007/BF00709660
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    Inoculation of rice with nitrogen-fixing bacteria —problems and perspectives (1987)
    Springer
    Biology and fertility of soils 4 (1987), S. 21-26 
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    ISSN: 1432-0789
    Keywords: Bacterial inoculation ; Rice yield ; Associative nitrogen fixation ; Azotobacter spp. ; Azospirillum spp. ; Pseudomonas spp. ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The present status and merits of inoculating rice with N2-fixing bacteria are discussed in the light of recent advances. Bacterial inoculation improves plant growth and rice yield but not uniformly. The yield response to inoculation is more pronounced in the presence of moderate levels of fertilizer N. Evidence for the establishment and activity of the inoculated bacteria is limited, and the poor survival of the inoculum under field conditions further complicates the effects of inoculation. There is no clear evidence that improved growth and mineral content following inoculation are due to increased N2 fixation. Beneficial effects of the inoculum on rice, such as plant growth promotion, N2 fixation and antagonism effects against pathogens need to be further investigated under laboratory and field conditions. Improved management practices, such as organic amendments, suitable water and soil management, selection of efficient microbial strains, selection of effective breeding lines with high associative nitrogen fixation, and better management of agrochemicals are some of the measures suggested for deriving benefits from bacterial associations with rice.
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    URL: http://dx.doi.org/10.1007/BF00280346
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    Organic and inorganic soil phosphates and acid phosphatase activity in the rhizosphere of 80-year-old Norway spruce [Picea abies (L.) Karst.] trees (1989)
    Springer
    Biology and fertility of soils 8 (1989), S. 128-133 
    Details
    ISSN: 1432-0789
    Keywords: Organic phosphates ; Rhizosphere ; Mycorrhizal roots ; Acid phosphatase ; Picea abies (L.) Karst. ; Norway spruce
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Inorganic and organic phosphates (P) were measured in bulk soil, rhizosphere soil and mycorrhizal rhizoplane soil of Norway spruce. Various methods of P extraction and estimation were compared. In addition, acid phosphatase activity and mycelial hyphae length were determined. In soil solutions from various locations, about 50% (range 35%–65%) of the total P was present as organic P. Compared to the bulk soil, the concentrations of readily hydrolysable organic P were lower in the rhizosphere soil and in the rhizoplane soil; this difference was particularly marked in the humus layer. In contrast, the concentrations of inorganic P either remained unaffected or increased. A 2- to 2.5-fold increase was found in the activity of acid phosphatase in the rhizoplane soil in comparison to the bulk soil. There was a positive correlation (r = 0.83***) between phosphatase activity and the length of mycelial hyphae. The results stress the role of organic P and of acid phosphatase in the rhizosphere in the P uptake by mycorrhizal roots of spruce trees grown on acid soils.
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    Seeding vs. vegetative propagations of the stem-nodulating green manure Sesbania rostrata (1988)
    Springer
    Biology and fertility of soils 6 (1988), S. 279-281 
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    ISSN: 1432-0789
    Keywords: Sesbania rostrata ; Green manure ; Biofertilizer ; Nitrogen fixation ; Stem nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Ratooning and stem cutting were compared with seeding in order to reduce the amount of seeds of Sesbania rostrata for green-manure growth. Both methods increased the biofertilizer yield highly significantly within a 6-week growth period.
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    URL: http://dx.doi.org/10.1007/BF00261012
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    Cellulolytic and pectolytic activity of streptomycetes isolated from root-free soil, rhizosphere and mycorrhizosphere of pine (Pinus sylvestris L.) (1989)
    Springer
    Biology and fertility of soils 7 (1989), S. 365-369 
    Details
    ISSN: 1432-0789
    Keywords: Streptomycetes ; Cellulolytic ; Pectolytic activity ; Pine ; Pinus sylvestris ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Our studies have revealed that streptomycetes inhabiting root-free soil and the root zone of pine trees differ in their capacity to produce cellulolytic and pectolytic enzymes. Most of the root-zone organisms but only a few of the root-free soil isolates exhibited cellulolytic activity. A few of the root-zone organisms but no soil isolate showed pectolytic activity. In general the cellulolytic activity was higher in cellulase producers from the root zone than in those derived from the root-free soil. The streptomycetes studied produced only endopolymethylgalacturonase. The mean total activity of this enzyme was higher in the rhizosphere isolates but the mean specific activity was higher in the mycorrhizosphere organisms.
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    URL: http://dx.doi.org/10.1007/BF00257834
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    Influence of soluble phosphorus fertilizer on the interaction between a vesicular-arbuscular mycorrhizal fungus and Azospirillum brasilense in barley (Herdeum vulgare L.) (1990)
    Springer
    Biology and fertility of soils 10 (1990), S. 57-60 
    Details
    ISSN: 1432-0789
    Keywords: Phosphorus fertilizer ; vesicular-arbuscular mycorrhizal fungus ; Azospirillum brasilense ; Glomus versiforme ; Barley ; Nitrogen fixation ; Nitrogen-15 ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Pot-culture studies were carried out to examine the response of barley (Hordeum vulgare L.) to inoculation with Azospirillum brasilense and Glomus versiforme, singly and/or in combination, under varying levels of nitrogenous [(15NH4)2SO4] and soluble phosphatic (single superphosphate) fertilizers. The interaction between both the endophytes led to increased growth and nutrition of the barley plants. Roots from plants inoculated with Azospirillum brasilense and Glomus versiforme exhibited very low acetylene reduction activity. N2 fixation in the plants increased with the increase in plant growth but the mycorrhiza alone gave a low level of N2 fixation in the plants compared to combined inoculation with both the endophytes.
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    URL: http://dx.doi.org/10.1007/BF00336125
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    Effect of active roots on the decomposition of soil organic materials (1990)
    Springer
    Biology and fertility of soils 10 (1990), S. 121-126 
    Details
    ISSN: 1432-0789
    Keywords: Biodegradation ; Nutrient levels ; Mineralization ; Rhizosphere ; Microenvironment ; Root exudates ; Priming effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The effect of one form of soil organic matter, such as living roots or root exudates on another form of soil organic matter, such as dead roots or incorporated litter and litter leachates, has been studied from various perspectives over the last 25 years. The effect seems to be either positive (priming) or negative (conserving). The present review concentrates on the conserving effect, measured as a decrease in 14CO2 released, in both field and greenhouse/growth chamber studies. The field experiments suggested that certain physical conditions in the soil, such as less available moisture or restricted aeration which led to lower microbial activity, explained the conserving effect of living roots on soil organic matter. Although more detailed greenhouse/growth chamber studies confirmed the conserving effect per se, it appears that biological rather than physical factors could better explain the reduction in the rate of decomposition of 14C-labelled plant residues in the presence of roots. However, a complex picture has emerged through a variety of postulates, all proposed in attempts to explain the conserving effect. Finally, the most recent studies have argued that the decrease in decomposition of labelled organic matter in planted soil is probably more apparent than real. A decrease in respired 14CO2 could be explained by an incorporation of 14C derived from old roots into the rhizosphere microbial populations of the living roots. To make any further progress on the fundamental question of how soil organic matter moves along its continuum from a living to a refractory state, the microenvironment needs to be examined at periodic intervals. New developments in improved histochemical and electron-probe microanalyses look promising.
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    Effect of phosphonate on the rhizosphere microflora and the development of root rot (Phytophthora cinnamomi) in avocado (Persea americana) and pepper-corn (Schinus molle) tree seedlings (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 13-17 
    Details
    ISSN: 1432-0789
    Keywords: Phosphonate ; Soil microorganisms ; Rhizosphere ; Phytophthora cinnamomi ; Phytophthora palmivora ; Root rot ; Avocado ; Schinus molle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Application to soil of 1 g (recommended rate) or 10 g l-1 of phosphonate did not affect the numbers of bacteria and fungi nor the proportions of actinomycetes and fungi antagonistic to Phytophthora cinnamomi. Foliar phosphonate applications to avocado seedlings (Persea americana) did not affect microbial numbers or the proportions of microbes in the rhizosphere capable of antagonizing P. cinnamomi. Mycelium of P. cinnamomi and zoospores of P. palmivora did not appear to respond to diffusates from excised roots of phosphonate-treated avocado and pepper-corn tree (Schinus molle) seedlings, respectively. However, less extensive lesions were observed on the roots of fungicide-treated avocado and pepper-corn tree seedlings exposed to P. cinnamomi and P. palmivora, respectively. The reduction in P. cinnamomi infection on pepper-corn tree seedlings appears to be brought about by additive rather than interactive effects of the resident soil microflora and foliar-applied phosphonate.
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    Bacteria-grazing amoebae in situ in the rhizosphere (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 83-87 
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    ISSN: 1432-0789
    Keywords: Amoebae ; Protozoa ; Rhizosphere ; Nutrient cycling ; Biocontrol ; Microaggregates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary An ultrastructural investigation of amoebae in situ in the rhizosphere showed that the protozoa are closely associated with soil aggregates and produce long pseudopodia that penetrate micropores. This could partly explain why bacteria are generally confined to the interiors of microaggregates. The presence of cytologically intact and partly digested bacteria in the food vacuoles indicates that rhizosphere bacteria are both ingested and digested by the amoebae. This digestion could lead to the recycling of P and N immobilized in rhizosphere microorganisms.
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    Occurrence of vesicular-arbuscular mycorrhizae with Amaranthaceae in soils of the Indian semi-arid region (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 140-144 
    Details
    ISSN: 1432-0789
    Keywords: Endogonaceous ; Vesicular-arbuscular mycorrhiza ; Endomycorrhiza ; Symbiosis ; Amaranthaceae ; Rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Some members of the family Amaranthaceae, which has mostly been reported as non-mycorrhizal, were examined for a symbiotic association with mycorrhizae in the semiarid and arid zones. Ten species belonging to five genera, Achyranthes, Aerva, Alternanthera, Amaranthus, and Celosia were examined, using 1.0-cm long root standards. Intercellular hyphae, vesicles and arbuscules were observed in the root cortex. The number of different types of spores in the rhizosphere soil of different plants ranged from one to three. The spores isolated represented nine species belonging to four genera, Glomus, Gigaspora, Sclerocystis, and Scutellospora. No correlation could be established between spore counts and either soil pH or soil moisture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336379
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  • 96
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    Diversity of diazotroph populations in the rhizosphere of maize (Zea mays L.) growing on different French soils (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 210-215 
    Details
    ISSN: 1432-0789
    Keywords: Rhizosphere ; Maize ; Bacillus circulans ; Enterobacteriaceae ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary We studied the dominant diazotrophs associated with maize roots and rhizosphere soil originating from three different locations in France. An aseptically grown maize plantlet, the “spermosphere model”, was used to isolate N2-fixing (acetylene-reducing) bacteria. Bacillus circulans was the dominant N2-fixing bacterium in the rhizosphere of maize-growing soils from Ramonville and Trogny, but was not found in maize-growing sandy soil from Pissos. In the latter soil, Enterobacter cloacae, Klebsiella terrigena, and Pseudomonas sp. were the most abundant diazotrophs. Azospirillum sp., which has been frequently reported as an important diazotroph accociated with the maize rhizosphere, was not isolated from any of these soils. The strains were compared for their acetylene-reducing activity in the spermosphere model. The Bacillus circulans strains, which were more frequently isolated, also exhibited significantly greater acetylene-reducing activity (3100 nmol ethylene day-1 plant-1) than the Enterobacteriaceae strains (180 nmol ethylene day-1 plant-1). This work indicates for the first time that Bacillus circulans is an important maizerhizosphere-associated bacterium and a potential plant growth-promoting rhizobacterium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335769
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  • 97
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    Variation in nodulation and N2 fixation by the Gliricidia sepium/Rhizobium spp. symbiosis in a calcareous soil (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 273-278 
    Details
    ISSN: 1432-0789
    Keywords: Genetic variability ; N-15 methods ; Nitrogen fixation ; Provenances ; Rhizobium strains ; Gliricidia sepium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Variation in nodulation and N2 fixation by the Gliricidia sepium/Rhizobium spp. symbiosis was studied in two greenhouse experiments. The first included 25 provenances of G. sepium inoculated with a mixture of three strains of Rhizobium spp. N2 fixation was measured using the 15N isotope dilution method 12 weeks after planting. On average, G. sepium derived 45% of its total N from atmospheric N2. Significant differences in fixation were observed between provenances. The percentage of N derived from atmospheric N2 ranged from 26 to 68% (equivalent to 18–62 mg N plant-1) and was correlated with total N in the plant (r=0.70; P=0.05). The second experiment included six strains of Rhizobium spp. and two methods of inoculation and the plants were harvested 14,35 and 53 weeks after planting. In the first harvest significant differences were found between the number of nodules and the percentage and amount of N2 fixed. There was also a significant correlation between the number of nodules and the amount of N2 fixed (r=0.92; P=0.05). In the final harvest no correlation was observed, although there were significant differences between the number of nodules and the percentage of N derived from the atmosphere. The amount of N2 fixed increased with time (from an average of 27% at the first harvest to 58% at the final harvest) and was influenced by the Rhizobium spp. strain and the method of inoculation. It ranged from 36% for Rhizobium sp. strain SP 14 to 71% for Rhizobium SP 44 at the last harvest. Values for the percentage of atmosphere derived N2 obtained by soil inoculation were slightly higher than those obtained by seed inoculation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335847
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  • 98
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    Electronic Resource
    The influence of blue-green algae on the biological amelioration of alkali soils (1991)
    Springer
    Biology and fertility of soils 11 (1991), S. 306-312 
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    ISSN: 1432-0789
    Keywords: Alkali soil ; Blue-green algae ; Calcium carbonate ; Gypsum ; Nitrogen fixation ; Organic matter ; Soil reclamation ; Sodic soil ; Waterlogged soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Virgin alkali (sodic) soils have a high pH and high exchangeable Na and are often barren. Blue-green algae, however, tolerate excess Na and grow extensively on the soil surface in wet seasons. Experiments using a highly degraded alkali soil (silt loam, pH 10.3, electrical conductivity 3.5 dS m-1, 90% exchangeable Na) were conducted in soil columns, with or without gypsum, in order to study the influence of waterlogging on the growth of indigenous and inoculated blue-green algae and hence, soil reclamation. The growth of indigenous blue-green algae was initially slow in alkali soil, due to the high pH and exchangeable Na, and depressed in gypsum-amended soil, due to excess Ca. Inoculation hastened the establishment of blue-green algae in both the unamended alkali soil and the gypsum-amended soil, overcoming the adverse influence of excess Na in the former and excess Ca in the latter. Gypsum was effective in amelioration (pH 9.05, electrical conductivity 1.2 dS m-1, 41% exchangeable Na after 11 weeks) but blue-green algae were ineffective even after 17 weeks. In combination with gypsum, blue-green algae had no additional effect, and the C and N increases due to the growth of indigenous or inoculated blue-green algae were insignificant. Alkali soil reclamation by biological methods requires mobilization of Ca from native soil calcite and the exchange of Ca for Na in the exchange complex. The ineffectiveness of blue-green algae was ascribed to their inability to mobilize Ca. It is argued that current theories favouring blue-green algae as a biological amendment to bring about alkali soil reclamation are untenable and are not comparable with an effective chemical amendment such as gypsum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335853
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  • 99
    Electronic Resource
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    Nitrogen fixation by Azospirillium brasilense in soil and the rhizosphere under controlled environmental conditions (1991)
    Springer
    Biology and fertility of soils 12 (1991), S. 100-106 
    Details
    ISSN: 1432-0789
    Keywords: Azospirillum ; 15N-isotope dilution ; Nitrogen fixation ; Acetylene reduction activity ; ARA ; Rhizosphere ; Mineral nitrogen ; Oxygen tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Acetylene reduction activity by Azospirillum brasilense, either free-living in soils or associated with wheat roots, was determined in a sterilised root environment at controlled levels of O2 tension and with different concentrations of mineral N. In an unplanted, inoculated soil nitrogenase activity remained low, at approximately 40 nmol C2H4 h-1 per 2kg fresh soil, increasing to 300 nmol C2H4 h-1 when malic acid was added as a C source via a dialyse tubing system. The N2 fixation by A. brasilense in the rhizosphere of an actively growing plant was much less sensitive to the repressing influence of free O2 than the free-living bacteria were. An optimum nitrogenase activity was observed at 10 kPa O2, with a relatively high level of activity remaining even at an O2 concentration of 20 kPa. Both NO inf3 sup- and NH inf4 sup+ repressed nitrogenase activity, which was less pronounced in the presence than in the absence of plants. The highest survival rates of inoculated A. brasilense and the highest rates of acetylene reduction were found in plants treated with azospirilli immediately after seedling emergence. Plants inoculated at a later stage of growth showed a lower bacterial density in the rhizosphere and, as a consequence, a lower N2-fixing potential. Subsequent inoculations with A. brasilense during plant development did not increase root colonisation and did not stimulate the associated acetylene reduction. By using the 15N dilution method, the affect of inoculation with A. brasilense in terms of plant N was calculated as 0.067 mg N2 fixed per plant, i.e., 3.3% of the N in the root and 1.6% in the plant shoot were of atmospheric origin. This 15N dilution was comparable to that seen in plants inoculated with non-N2-fixing Psudomonas fluorescens.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00341483
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  • 100
    Electronic Resource
    Electronic Resource
    Use of aliette, a basipetally translocated antimicrobial compound, to enhance rhizophere colonization and nodulation by root-nodule bacteria (1991)
    Springer
    Biology and fertility of soils 12 (1991), S. 141-146 
    Details
    ISSN: 1432-0789
    Keywords: Aliette ; Colonization ; Fungicide ; Rhizobia ; Rhizosphere ; Bradyrhizobium japonicum ; Alfalfa ; Medicago sativa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A method was developed to improve the colonizing ability of inoculated strains of root-nodule bacteria using aliette (aluminum tris-O-ethyl phosphonate), a basipetally translocated fungicide. Aliette applied to seeds of alfalfa inoculated with an aliette-resistant strain of Rhizobium meliloti increased the numbers of R. meliloti in the rhizosphere after 3 but not 37 days, increased the number of nodules, and with some seed treatments, increased the growth of alfalfa. The enhanced colonization by R. meliloti as a result of seed treatment with aliette lasted for at least 31 days for alfalfa, although plant weights did not increase, Colonization by R. meliloti was further enhanced if seeds and foliage were treated with the fungicide. Coating seeds or sparaying the foliage with aliette also increased the number and weight of nodules and nitrogenase activity in soybeans inoculated with an aliette-resistant strain of Bradyrhizobium japonicum. The stimulation of B. japonicum in the rhizosphere and of nodulation was evident with successive plantings of soybeans if the seeds for each planting were treated with the chemical, but aliette did not increase the yield of inoculated soybeans in the subsequent plantings. With only the seeds of the first planting of inoculated soybeans treated with aliette, the numbers of B. japonicum in the rhizosphere of subsequent plantings were only occasionally greater and the numbers of nodules on the later plantings were not increased. We suggest that root colonization, nodulation, and N2 fixation by Rhizobium and Bradyrhizobium may be enhanced by the use of basipetally translocated antimicrobial compounds together with root-nodule bacteria that are resistant to those compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00341491
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