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  • Articles  (213)
  • Nitrogen fixation  (213)
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (213)
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  • 1
    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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  • 2
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    Biology and fertility of soils 30 (2000), S. 363-373 
    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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  • 3
    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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  • 4
    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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  • 5
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    Biology and fertility of soils 30 (2000), S. 485-491 
    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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  • 6
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    Biology and fertility of soils 29 (1999), S. 141-145 
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
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    Biology and fertility of soils 27 (1998), S. 60-64 
    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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  • 11
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    Biology and fertility of soils 27 (1998), S. 393-399 
    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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  • 12
    ISSN: 0931-1890
    Keywords: Key words Drought stress ; Fertilization ; Irrigation ; Nitrogen fixation ; Nodule structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effects of water stress and nitrogen availability on leaf water potential, nitrogenase activity, and growth was studied in a pot experiment with Leucaena leucocephala seedlings. Water stress was imposed on fertilized and unfertilized plants after inoculation with Rhizobium. Non-inoculated seedlings were used as control plants. Water stress lowered leaf water potential in all seedlings after 14 days of treatment. In inoculated seedlings, fertilized plants were more sensitive to water stress than unfertilized plants, as shown by a higher leaf water potential in plants of the latter treatment. Uninoculated and fertilized seedlings were most affected by water stress. This indicates that Rhizobium might increase stress tolerance in unfertilized seedlings at moderate water stress levels. The combined effects of water stress and applied fertilizers resulted in cessation of nitrogen fixation. Nitrogen fixation came to a complete stop after 22 days of water stress in fertilized seedlings. The different treatments were accompanied by anatomical changes of nodule structure. It is hypothesised that the leaf water potential may be used as an indicator to predict changes in nitrogen fixation in legume tree/shrub species during periods of water stress.
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  • 13
    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.
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  • 14
    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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  • 15
    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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  • 16
    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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  • 17
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    Biology and fertility of soils 25 (1997), S. 407-415 
    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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  • 18
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    Biology and fertility of soils 25 (1997), S. 169-174 
    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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  • 19
    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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  • 20
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    Biology and fertility of soils 25 (1997), S. 209-210 
    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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  • 21
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    Biology and fertility of soils 25 (1997), S. 211-223 
    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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  • 22
    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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  • 23
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    Biology and fertility of soils 21 (1996), S. 293-302 
    ISSN: 1432-0789
    Keywords: Key words Ammonium excretion ; Azorhizobium caulinodans ; Auxine ; 2 ; 4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Rice ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Rice seedlings developed nodule-like tumors (para-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-root primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice para-nodules and in root tissues around tumor bases. The infection with A. caulinodans followed a typical “crack-entry” invasion at places where para-nodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in intercellular spaces of the induced tumors and betwen root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like structures. N2 fixation by tumor-inhabiting Azorhizobium sp. was increased at low O2 tensions (1.5–3 kPa) compared with an untreated control. Only a little activity remained at O2 tensions of 5 kPa and above. The present results confirm that root-tumor induction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.
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  • 24
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    Biology and fertility of soils 23 (1996), S. 50-56 
    ISSN: 1432-0789
    Keywords: Agroforestry ; 15N ; Nitrogen fixation ; Phenolics ; 13C ; Tree fallows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The natural abundance of 15N and 13C, conventional soil analyses, and biomass production by maize were used to study the influence of five tropical tree species on soils and their fertility. The experiment was conducted in Morogoro, Tanzania, to compare Cassia (Senna) siamea, Eucalyptus camaldulensis, E. tereticornis (all non-N2-fixing), Leucaena leucocephala, Prosopis chilensis (both N2-fixing), and a grass fallow. Maize biomass production, which was correlated with N uptake (P=0.001), was higher on soils from plots with 5-year-old Leucaena and Prosopis spp. compared to the grass fallow, while other tree species had less favourable effects on maize growth. The per cent N was higher in soil and δ15N of soil total N was lower under Prosopis sp. compared to soil under other tree species, which suggests an input from N2 fixation by Prosopis sp. A transfer of fixed N to maize or to understorey grass species was, however, not indicated by the 15N natural abundance. Prosopis sp. contributed more C to the soil than the other four tree species; the difference in δ13C between soils from Prosopis sp. plots and from grass fallow plots showed that the tree contributed 11% to the total C of the soil over a period of 8 years. The leaves of the N2-fixing species had a low ratio of lignin+phenols to N, and maize growth was negatively correlated with this parameter. The Eucalyptus spp. had leaves with a high lignin+phenols to N ratio, contributed very little C to the soil, and lowered the soil pH.
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  • 25
    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.
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  • 26
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    Biology and fertility of soils 23 (1996), S. 243-248 
    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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  • 27
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    Biology and fertility of soils 23 (1996), S. 362-367 
    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.
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  • 28
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    Biology and fertility of soils 21 (1996), S. 77-83 
    ISSN: 1432-0789
    Keywords: Denitrification ; Field experiment ; Acetylene inhibition technique ; Nitrate ; Soil moisture ; Vicia faba ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Denitrification rates were studied using the C2H2 inhibition technique in a 2-year field experiment within plots of nodulated and non-nodulated faba beans, ryegrass, and cabbage. Denitrification rates ranged from 14.40 to 0.02 ng N2O−N g−1 soil dry weight h−1. Mean denitrification increased fourfold in plots of N2−fixing Vicia faba compared to non-nodulated V. faba mutant F48, Lolium perenne, and Brassica oleracea. The results with and without C2H2 treatment indicate that in the field the major part of this enhanced denitrification led to the endproduct N2 rather than to the ozone-degrading N2O. Higher denitrification rates of plots with N2−fixing plants in September seemed to be caused by an increase in soil NO inf3 sup- of about 20 kg ha−1 found between July and August. Soil NO inf3 sup- and soil moisture explained 67% of the variation in denitrification rates of the different soil samples over the growing seasons in the 2 years. Soil moisture explained 44% of the variation for soil planted with N2−fixing plants and 62% for soil planted with non-fixing plants. Positive exponential relationships were obtained between denitrification rates and soil nitrate (r=0.71) and soil moisture (r=0.82).
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  • 29
    ISSN: 1432-0789
    Keywords: Key words 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 endophytic 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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  • 30
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    Biology and fertility of soils 21 (1996), S. 293-302 
    ISSN: 1432-0789
    Keywords: Ammonium excretion ; Azorhizobium caulinodans ; Auxine 2.4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Rice ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Rice seedlings developed nodule-like tumors (para-nodules) along primary and secondary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Histologically, these tumors appeared as cancerous out-grown lateral-root primordes and were thus comparable with stem nodules of the legume Sesbania rostrata. Azorhizobium caulinodans (a diazotroph known as a specific endophyte of Sesbania rostrata) was introduced and became established inside rice para-nodules and in root tissues around tumor bases. The infection with A. caulinodans followed a typical “crack-entry” invasion at places where paranodule tumors had emerged through the root cortex and epidermis. The bacteria settled with high cell densities in intercellular spaces of the induced tumors and between root cortical cells. Infection of plant cells took place both in the epidermis and in cortical tissue. Intracellularly established A. caulinodans was found inside the cytoplasm, surrounded by membrane-like structures. N2 fixation by tumor-inhabiting Azorhizobium sp. was increased at low O2 tensions (1.5–3 kPa) compared with an untreated control. Only a little activity remained at O2 tensions of 5 kPa and above. The present results confirm that root-tumor induction offers a suitable method of establishing diazotrophs endophytically in the roots of gramineous crops.
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  • 31
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    Biology and fertility of soils 23 (1996), S. 50-56 
    ISSN: 1432-0789
    Keywords: Key words Agroforestry ; 15N ; Nitrogen fixation ; Phenolics ; 13C ; Tree fallows
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The natural abundance of 15N and 13C, conventional soil analyses, and biomass production by maize were used to study the influence of five tropical tree species on soils and their fertility. The experiment was conducted in Morogoro, Tanzania, to compare Cassia (Senna) siamea, Eucalyptus camaldulensis, E. tereticornis (all non-N2-fixing), Leucaena leucocephala, Prosopis chilensis (both N2-fixing), and a grass fallow. Maize biomass production, which was correlated with N uptake (P=0.001), was higher on soils from plots with 5-year-old Leucaena and Prosopis spp. compared to the grass fallow, while other tree species had less favourable effects on maize growth. The per cent N was higher in soil and δ15N of soil total N was lower under Prosopis sp. compared to soil under other tree species, which suggests an input from N2 fixation by Prosopis sp. A transfer of fixed N to maize or to understorey grass species was, however, not indicated by the 15N natural abundance. Prosopis sp. contributed more C to the soil than the other four tree species; the difference in δ13C between soils from Prosopis sp. plots and from grass fallow plots showed that the tree contributed 11% to the total C of the soil over a period of 8 years. The leaves of the N2-fixing species had a low ratio of lignin+phenols to N, and maize growth was negatively correlated with this parameter. The Eucalyptus spp. had leaves with a high lignin+phenols to N ratio, contributed very little C to the soil, and lowered the soil pH.
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  • 32
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    Biology and fertility of soils 23 (1996), S. 243-248 
    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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  • 33
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    Biology and fertility of soils 23 (1996), S. 362-367 
    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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  • 34
    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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  • 35
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    Biology and fertility of soils 20 (1995), S. 57-62 
    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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  • 36
    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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  • 37
    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.
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  • 38
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    Biology and fertility of soils 20 (1995), S. 147-150 
    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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  • 39
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    Biology and fertility of soils 17 (1994), S. 1-8 
    ISSN: 1432-0789
    Keywords: Ammonium excretion ; Azospirillum brasilense ; Auxine ; 2,4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Maize ; Zea mays ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Maize seedlings develop nodule-like tumour knots (para-nodules) along primary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Inoculated NH 4 + -excreting Azospirillum brasilense cells were shown to colonize these tumours, mostly intracellularly, promoting a high level of N2 fixation when microaerophilic conditions were imposed. The nitrogenase activity inside the para-nodules was less sensitive to free O2 than in non-para-nodulating roots. Both light and electron microscopy showed a dense bacterial population inside intact tumour cells, with the major part of the cell infection along a central tumour tissue. The bacteria colonized the cytoplasm with a close attachment to inner cell membranes. In an auxin-free growth medium, young 2,4-D-induced para-nodules grew further to become mature differentiated root organs in which introduced bacteria survived with a stable population. These results provide evidence that gramineous plants are potentially able to create a symbiosis with diazotrophic bacteria in which the NH 4 + -excreting symbiont will colonize para-nodule tissue intracellularly, thus becoming well protected.
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  • 40
    ISSN: 1432-0789
    Keywords: Fertilizer use efficiency ; Intercropping ; Natural 15N abundance ; Nitrogen fixation ; Pigeonpea ; Sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to obtain the N balance sheet for sole crops and intercrops of sorghum [Sorghum bicolor (L.) Moench] and pigeonpeas [Cajanus cajan (L.) Millsp.]. Intercropping gave a significant advantage over sole cropping in terms of dry matter production and grain yield, as calculated on the basis of the land equivalent ratio and area-time equivalent ratio. The N fertilizer use efficiency and atmospheric N2 fixation by pigeonpea were estimated using 15N-labeling and natural abundance methods. The N fertilizer use efficiency of sorghum was unaltered by the cropping system, while that of the pigeonpea was greatly reduced by intercropping. Although intercropping increased the fractional contribution of fixed N to the pigeonpeas, no significant difference was observed between the cropping systems in total symbiotically fixed N. There was no evidence of a significant transfer of N from the pigeonpea to the sorghum. This study showed that use of soil N and fertilizer N by pigeonpeas was almost the same as that by sorghum in sole cropping, indicating the potential competence of pigeonpeas to exploit soil N. However, when N was exhausted by a companion crop in intercropping, the pigeonpea crop increased its dependency on atmospheric N2 fixation. We conclude that knowledge of how N from different sources is shared by companion crops is a prerequisite to establishing strategies to increase N use, and consequently land productivity, in intercropping systems.
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  • 41
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    Biology and fertility of soils 18 (1994), S. 37-41 
    ISSN: 1432-0789
    Keywords: Available nutrients ; Insecticides ; Microortanisms ; Nitrogen fixation ; Phosphate solubilization ; Rhizosphere soil ; Rice yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to investigate the effects of 1,2,3,4,5,6-hexachlorocyclohexane (BHC), phorate, carbofuran, and fenvalerate, at their recommended doses, on some chemical and microbiological properties of the rhizosphere soil in relation to rice yields. In general, the insecticides had a beneficial effect on rhizosphere soil properties. Carbofuran strongly stimulated the mineralization of organic C. BHC and phorate led to the retention of less total N in the soil. BHC released more NH inf4 sup+ -N than the other insecticides. Phorate, however, liberated the most NO inf3 sup- -N. Phorate and fenvalerate released more available P than BHC and carbofuran did. All the insecticides stimulated the proliferation of aerobic non-symbiotic N2-fixing and phosphate-solubilizing microorganisms, resulting in an overall increase in rice yield. BHC had the greatest effect on rice yields, followed by phorate.
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  • 42
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    Biology and fertility of soils 18 (1994), S. 231-236 
    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.
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  • 43
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    Trees 8 (1993), S. 99-103 
    ISSN: 1432-2285
    Keywords: Robinia pseudoacacia L. ; Hydrogen uptake ; Hydrogenase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Hydrogen uptake is thought to increase the efficiency of nitrogen fixation by recycling H2 produced by nitrogenase that would otherwise be lost by diffusion. Here we demonstrate the capacity of eight Rhizobium strains to take up molecular hydrogen. Uptake by nodule homogenates from Robinia pseudoacacia was measured amperometrically under nitrogenase repression. Markedly lower activities were found than in soybean nodules. In addition hydrogenase activity was detected by the ability of bacteroids to reduce methylene blue in the presence of hydrogen. It was demonstrated that hydrogenase structural genes are present in the black locust symbiont, Rhizobium sp. strain R1, using hybridization with a plasmid, which contained hydrogenase genes from R. leguminosarum bv. viceae.
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  • 44
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    Biology and fertility of soils 15 (1993), S. 275-278 
    ISSN: 1432-0789
    Keywords: Peanuts ; Arachis hypogaea ; Continuous cropping ; Nitrogen fixation ; Bradyrhizobium spp. ; Effectiveness of rhizobia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The objective of this study was to assess the number and effectiveness of peanut rhizobia in soils of the major peanut-growing areas of Thailand. Three cropping areas, (1) continuously cropped with peanuts, (2) continuously cropped with non-legumes, and (3) non-cultivated fields, were chosen in each region. Peanut rhizobia were found in the soil at 38 to 55 sites sampled. Cultivated fields with a peanut cultivation history contained (as estimated by most probable numbers) an average of 1.6×103 cells g-1 of soil. The numbers of peanut rhizobia in most of the fallow fields and some of the noncultivated shrub or forest locations were much the same as at the sites where Arachis hypogaea was cultivated. In contrast, there were no or few (28–46 cells g-1 soil) peanut rhizobia in the majority of fields continuously cultivated with sugarcane, cassava, corn, and pineapple. It appears that in these areas the indigenous peanut rhizobial populations are not adequate in number for a maximal nodulation of peanuts. A total of 343 Bradyrhizobium isolates were tested for effectiveness and were found to vary widely in their ability to fix N2. In some areas the majority of rhizobia were quite effective while in others they were less effective than the inoculum strain THA 205 recommended in Thailand.
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  • 45
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    Biology and fertility of soils 16 (1993), S. 299-301 
    ISSN: 1432-0789
    Keywords: A N value ; 15N ; Nitrogen fixation ; Glycine max ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Pot experiments were conducted with two soils, from Rottenhaus and Seibersdorf in Austria, to ascertain whether the rate of fertilizer N application and the test crop would influence the amount of N available in the soil as assessed by the A-value method. 15N-labelled fertilizer was applied at rates of 10, 25, 40, 60, and 100 mg N kg-1 soil, corresponding approximately to 20, 50, 80, 120 and 200 kg N ha-1 respectively, and two crop species, barley (Hordeum vulgareL.) and non-nodulating soybean (Glycine max L.) were used to determine the soil A N value under the various fertilizer regimes. The results showed that the Rottenhaus soil had a higher A N value than the Seibersdorf soil, suggesting that the former was more fertile than the latter. The A N values of both soils were significantly affected by the level of N application. When grown in the same soil, the two test crops showed significantly different fertilizer use efficiency and per cent N derived from fertilizer when the rate of N application exceeded 20 kg ha-1. Thus, the A N value as determined by the two test crops differed significantly for the same soil when the rate of N application was greater than 20 kg/ha. The difference was greater when the soil fertility level was high. The dependence of the A N value on the level of N application and the species of crop seriously compromises the suitability of this method for determining plant-associated N2 fixation. Hence, considerable caution is required when using this method to estimate plant-associated N2 fixation.
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  • 46
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    Biology and fertility of soils 15 (1993), S. 35-38 
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Eucalyptus saligna ; Albizia falcataria ; Pontoscolex corethrurus ; Litterfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Tree species differ in the quantity and quality of litter produced, and these differences may significantly affect ecosystem structure and function. I examined the importance of tree species in determining earthworm densities in replicated stands of Eucalyptus saligna Sm. and Albizia falcataria (L.) Fosberg, and in mixed stands (25% albizia and 75% eucalyptus). Mean earthworm densities ranged from 92 m-2 in the pure eucalyptus, to 281 m-2 in the mixture, and a maximum of 469 m-2 in the pure albizia stands. Only two earthworm species were present, Pontoscolex corethrurus and Amynthas gracilis. Leaf biomass on the forest floor was highest in the pure eucalyptus and lowest in the pure albizia stands, whereas the annual fine litterfall production was lowest in the pure eucalyptus and highest in the albizia stands. The N content of fine litterfall was correlated positively with earthworm density, and the fine litterfall biomass: N ratio was correlated negatively with earthworm density. Greater leaf biomass on the forest floor under eucalyptus stands despite lower rates of litterfall suggests that litter quality, rather than litter quantity, was primarily responsible for the greater earthworm density in the albizia stands. Some biogeochemical effects of tree species in the tropics may be mediated through effects on earthworm populations.
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  • 47
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    Biology and fertility of soils 15 (1993), S. 73-78 
    ISSN: 1432-0789
    Keywords: Firewood crops ; Green-leaf manure ; Macronutrients ; Nodulation ; Nitrogen fixation ; Sesbania spp. ; Acetylen reduction assay ; ARA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In three field trials conducted during the summer season of 1986, 1987 and 1989 in an alkaline soil, 17 accessions of annual Sesbania spp. were evaluated for nodulation, N2 fixation (acetylene reduction assay), dry weight of roots and shoots, woody biomass production, and nutrient uptake. At 50 days after sowing all the accessions were effectively nodulated (average 36.4 root nodules plant-1) with a high nodule score (3.4). There was a lot of variation in nodule volume and mass and in acetylene reduction activity but not in N content (5.2%). N uptake in shoots, roots and nodules averaged 639, 31, and 13 mg plant-1, respectively, and much of the fixed N remained in shoots. Accessions of ‘S. cannabina’ complex performed better than others. S. rostrata had poor root nodulation but exhibited excellent stem nodulation (300 nodules plant-1) even though not inoculated with Azorhizobium sp. Average concentrations of N, P, K, S, Ca, and Mg in the shoots were high, at 3.2, 0.28, 1.5, 0.28, 1.5, and 0.4% respectively, and Na was low (0.15%), reflecting the usefulness of Sesbania spp. as an integrated biofertilizer source. Green matter production was 26.0 Mg ha-1 (5.9 Mg dry matter) and N uptake was 158 kg ha-1, 54 days after sowing. Average woody biomass of six accessions at maturity, 200 days after sowing, was high (19.9 Mg ha-1), showing its potential for shortterm firewood production. Total nutrient uptake for production of woody biomass (200 days of growth) was no more demanding than growing the plant to the green-manuring stage of 50–60 days' growth.
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  • 48
    ISSN: 1432-0789
    Keywords: δ 15N ; Elevation ; Nitrogen fixation ; Non-nodulating ; Glycine max ; Soybeans ; Isolines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Dissimilarities in soil N uptake between N2-fixing and reference non-N2-fixing plants can lead to inaccurate N2 fixation estimates by N difference and 15N enrichment methods. The natural 15N abundance (δ 15N) method relies on a stabilized soil 15N pool and may provide reliable estimates of N2 fixation. Estimates based on the δ 15N and differences in N yield of nodulating and non-nodulating isolines of soybean were compared in this study. Five soybeans from maturity groups 00, IV, VI, and VIII and their respective non-nodulating isolines were grown at three elevations differing in ambient temperature and soil N availability. Despite large differences in phenological development and N yield between the non-nodulating isolines, the δ 15N values measured on seeds were relatively constant within a site. The δ 15N method consistently produced lower N2 fixation estimates than the N difference method, but only in three of the 15 observations did they differ significantly. The average crop N derived from N2 fixation across sites and maturity groups was 81% by N difference compared to 71% by δ 15N. The magnitude of difference between the two methods increased with increasing proportions of N derived from N2 fixation. These differences between the two methods were not related to differences in total N across sites or genotypes. The low N2 fixation estimates based on δ 15N might indicate that the nodulating isolines had assimilated more soil N than the non-nodulating ones. A lower variance indicated that the estimates by N difference using non-nodulating isolines were more precise than those by δ 15N. Since the differences between the estimates were large only at high N2 fixation levels (low soil N availability), either method may be used in most situations when a non-nodulating isoline is used as the reference plant. The δ 15N method may have a comparative advantage over N difference and 15N enrichment methods in the absence of a suitable non-N2-fixing reference plant such as a non-nodulating isoline.
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  • 49
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Photosynthetic bacteria ; Stem nodules ; Aeschynomene scabra ; Sesbania rostrata ; Azorhizobium caulinodans ; Erythrobacter sp. ; Roseobacter denitrificans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Bradyrhizobial strain BTAi 1 nodulates both stems and roots of Aeschynomene spp. Previous work has shown that it contains bacteriochlorophyll a and forms photosynthetic reaction centers, and has provided indirect evidence of photosynthesis by bacteroids within stem nodules. Here we report physiological and biochemical characteristics of BTAi 1 ex planta, which also suggest the presence of photosynthetic activity. Light-stimulated uptake of 14CO2 by BTAi 1 was detected at all stages of growth. Inhibitors of photosynthesis, 1,10-orthophenanthroline and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and the uncoupler NH4Cl, immediately suppressed light-driven 14CO2 uptake and increased O2 uptake. BTAi 1 is strictly aerobic and was unable to grow without organic C even in the light; also, it was unable to grow chemoautotrophically in an atmosphere enriched with H2 and CO2. In micro-aerobic conditions, strain BTAi 1 expressed acetylene reducing activity ex planta in an N-free medium. The highest rates of light-stimulated 14CO2 uptake and acetylene-reducing activity occurred during the exponential and early stationary phases of growth. Acetylene-reducing rates at a low glucose concentration were increased following a light-dark cycle in comparison with continuous dark conditions.
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  • 50
    ISSN: 1432-0789
    Keywords: Typic cryoboroll ; N yield ; 15N ; Root length ; Grass-legume intercrop ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Barley-field pea intercrops have been shown to increase N yield when grown under cryoboreal subhumid conditions. In this study, we extended previous research by testing the hypotheses that (1) the intercropped field pea fixes a greater proportion of its shoot and root N than does sole-cropped field pea; (2) N is transferred from the annual legume to the cereal during the growing season; and (3) root production is greater under intercropped than sole-cropped conditions. Unconfined microplots seeded to barley, field peas, or a barley-field pea intercrop were fertilized with N at 10 kg ha-1 as (NH4)2SO4 (5.21 atom % 15N excess). Both the intercropped and sole-cropped barley derived more than 93% of their N from the soil. In contrast, 40% of N in the intercropped field pea was derived from soil. This study provided no evidence for transfer of N from the legume to the cereal. On average, the proportion of N derived from air by both pea intercrops was 39% higher than that derived by the sole-cropped pea. Root length determined by a grid intersection method following digitization using an image analyzer tended to be higher under intercropping than in sole crops. We conclude that even on fertile soils benefits may accrue from annual intercropping that includes a legume. The benefits arise from (1) increased N production, (2) greater N-fixation efficiency, and/or (3) more shoot and root residue-N mineralization for subsequent crops.
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  • 51
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    Biology and fertility of soils 13 (1992), S. 165-172 
    ISSN: 1432-0789
    Keywords: Azospirillum brasilense ; 15N-isotope enrichment ; Nitrogen fixation ; Auxine ; 2,4-dichlorphenoxy acetic acid ; 3,5-dichlor-phenoxy acetic acid ; Acetylene reduction assay ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wheat seedlings, treated with the auxine 2,4-dichlor-phenoxy acetic acid (2,4-D) during germination developed only a residual root system. Root elongation was extremely restricted and root tips were deformed to thick club-shaped tumours. When 2,4-D was added in a later stage of plant growth the plants developed additional nodule-like knots along primary roots. Root and shoot dry-matter production was slightly repressed in all 2,4-D treatments and N translocation from roots to shoots was repressed as well. When transferred to an auxine-free growth medium, the 2,4-D-affected roots were not capable of complete recovery. In plants inoculated gnotobiotically with Azospirillum brasilense, either with the wild type or with the NH 4 + -excreting mutant strain C3, a 2,4-D addition increased rhizosphere acetylene-reduction activity at pO2 1.5 kPa. The O2 sensitivity of root-associated nitrogenase activity tended to be reduced. The number of root-colonizing bacteria, at approximately 108 colony-forming units (cfu) per g dry root, was similar in the 2,4-D treatments and untreated controls. Plant treatment with high concentrations of the chemical isomer 3,5-dichlor-phenoxy acetic acid (3,5-D) did not have comparable effects, either on plant development or on rhizosphere-associated nitrogenase activity. Root-tumour tissue inhabited by A. brasilense showed purple staining when subjected to a tetrazolium chloride solution, which may indicate intensive local nitrogenase activity in this tissue. Exposed to an 15N2-enriched atmosphere, plants treated with 2,4-D and with A. brasilense incorporated significantly higher amounts of 15N than untreated controls. In all cases the highest values of 15N enrichment were found following inoculation with the NH 4 + -excreting mutant strain C3.
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  • 52
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    Trees 5 (1991), S. 227-231 
    ISSN: 1432-2285
    Keywords: Robinia pseudoacacia L. ; Nitrate ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Experiments with black locust (Robinia pseudoacacia L.) seedlings grown under strictly controlled laboratory conditions indicated that the availability of nitrate has a marked impact on nitrogen fixation. When nitrate concentrations were very low, both nodulation and seedling growth were impaired, whereas nitrate concentrations high enough to promote plant growth strongly inhibited symbiotic nitrogen fixation. When nitrate was added to the growth medium after infection, nodulation and nitrogen fixation of the seedlings decreased. This effect was even more marked when nitrate was applied before infection with rhizobia. Higher nitrogen concentrations also reduced nodule number and nodule mass when applied simultaneously with the infecting bacteria. The contribution of symbiotic nitrogen fixation to black locust shoot mass by far exceeded its effects on shoot length and root mass. When nitrate availability was very low, specific nitrogen fixation (i. e. nitrogenase activity per nodule wet weight) was improved with increasing nitrogen supply, but rapidly decreased with higher nitrogen concentrations.
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  • 53
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    Biology and fertility of soils 11 (1991), S. 210-215 
    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.
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  • 54
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    Biology and fertility of soils 11 (1991), S. 273-278 
    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.
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    Biology and fertility of soils 11 (1991), S. 306-312 
    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.
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    Biology and fertility of soils 12 (1991), S. 100-106 
    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.
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  • 57
    ISSN: 1432-0789
    Keywords: Ulex gallii ; Legume ; Nitrogenase activity ; Nitrogen fixation ; Acetylene reduction activity ; Phosphorus fertilizer ; Forest soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary N2(C2H2) fixation by Ulex gallii Planchon (dwarf or autumn flowering gorse/furze) seedlings was determined following 8 months of growth (December-August) in the glasshouse in a very acid, N- and P-deficient forest soil. Application of Na2HPO4·12H2O or North African ground rock phosphate fertilizer was essential for growth, nodulation and C2H2 reduction activity. Overall, both the sodium phosphate and the rock phosphate were equally effective P sources and the maximum acetylene reduction by intact roots was measured as 4.09 and 4.69 μmol C2H4g-1 fresh weight nodule h-1, respectively. Applied NH4Cl severely inhibited nodulation and restricted acetylene reduction activity but not seedling growth. The results are discussed in relation to the spread of U. gallii in the south of Ireland and its potential as a leguminous nurse crop for Sitka spruce on the very impoverished forest soils of the region.
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  • 58
    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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  • 59
    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).
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  • 60
    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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  • 61
    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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  • 62
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    Biology and fertility of soils 7 (1989), S. 269-274 
    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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  • 63
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    Biology and fertility of soils 8 (1989), S. 356-368 
    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.
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  • 64
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    Plant and soil 114 (1989), S. 63-68 
    ISSN: 1573-5036
    Keywords: Azolla pinnata ; Nitrogen fixation ; N yield ; Oryza sativa ; Urea-N
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Application of 0, 30, 60, 90 and 120 kg N ha−1 of urea (U) in split doses with (and without)Azolla pinnata, R. Brown was studied for three consecutive seasons under planted field condition. Fresh weight (FW), acetylene reduction activity (ARA) and N yield of Azolla were found to be maximum 14 days after inoculation (DAI). Among the different treatments, maximum Azolla growth was recorded in no N control. The FW, ARA and N yield of Azolla were inhibited increasingly with the increase in N levels. Irrespective of season, FW and N yield of Azolla were inhibited only a small extent with 90 kg N ha−1 U, beyond which the inhibition was pronounced. ARA was inhibited only slightly up to 60 kg N ha−1 of U. Grain yield and crop N uptake of rice increased significantly up to 90 kg N ha−1 of U (alone or in combination with Azolla) in the dry seasons (variety IR 36) and up to 60 kg N ha−1 U in the wet season (variety CR 1018).
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  • 65
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    Biology and fertility of soils 6 (1988), S. 279-281 
    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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  • 66
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    Biology and fertility of soils 6 (1988), S. 39-44 
    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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  • 67
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    Biology and fertility of soils 5 (1987), S. 83-87 
    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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  • 68
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    Biology and fertility of soils 4 (1987), S. 61-66 
    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.
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  • 69
    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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    Biology and fertility of soils 4 (1987), S. 15-19 
    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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    Biology and fertility of soils 4 (1987), S. 9-14 
    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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  • 72
    ISSN: 1573-5036
    Keywords: Foliar fertilization ; Fertilizer uptake efficiency ; Late fertilization ; Nitrogen-15 ; Nitrogen fixation ; Nitrogen translocation ; Soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Field experiments were conducted to determine the effects of the amount, time and method of fertilizer N application on the efficiency of N uptake, N2 fixatio and yield of soybean. Soil and foliar fertilizer N, applied during the pod-filling stage were absorbed by plants with equal and high efficiency, compared to an appreciably lower utilization efficiency for N applied before seedling emergence. These results reveal that the soybean roots were active in N uptake during these late stages of growth. Nitrogen fertilization during pod-filling resulted in significant yield increases over the control treatment which received an early application of 20 Kg N/ha. Seed yield increases were, however, more pronounced than total dry matter yield, and virtually all of the late-applied N was translocated into the pods. Nitrogen fixation in soybean was not influenced by the application of 40 kg N/ha to plants as soil or foliar N during the pod-filling stage. However, 80 kg N/ha supplied during pod-filling as 40 kg soil plus 40 kg foliar N/ha significantly reduced the amount of N2 fixed. The results obtained in these studies suggest that inadequate N supply during pod-filling limited soybean yields, and that by the judicious application of fertilizer N during the late stages of growth, it was possible to enhance soybean yields without necessarily inhibiting N2 fixation.
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  • 73
    ISSN: 1573-5036
    Keywords: Azolla ; Blue green alga ; Evapo-transpiratio chamber ; Humidity ; Light condition ; Nitrogen fixation ; Plant environment ; Symbiotic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The construction and application of a new type of growth chamber, in which different growth conditionsi.e.: temperature, humidity, pH, light intensity, light colour, change in nutrient composition and gas exchange can easily be controlled, are presented. The method has previously been applied to twoAzolla speciesviz. Azolla filiculoides, which is cold tolerant andAzolla pinnata (distinguished in Vietnam as the form Xanh), which is heat tolerant. In the growth chamber natural growth conditions of the Azolla —Anabaena azollae symbiotic association were imitated as much as possible. For testing the system, methods discussed earlier8,14 and some previously presented data, concerning photosynthetic activities, such as oxygen evolution and nitrogen fixation (acetylene reduction) of twoAzolla species39, were partially used. Biomass ofA. filiculoides was measured and reactions to its environment at conditions when grown in the field and in the growth chamber, were studied. Growth and photosynthesis measurements were performed under special light conditions and with whole plants grown under laboratory conditions. Anthocyanin synthesis was studied in relation with humidity. Anthocyanin spectra were analyzed by means of a spectrum-deconvolution method.
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  • 74
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    Plant and soil 100 (1987), S. 157-169 
    ISSN: 1573-5036
    Keywords: Legume ; Nitrogen fixation ; Nodule ; Translocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrogen (N2) fixed by Rhizobium bacteroids in the legume nodule is excreted as ammonia to the surrounding host cell where it is efficiently assimilated into the amide group of glutamine. Generally glutamine is a minor exported solute of nitrogen, being further metabolised to asparagine in temperate species and to the ureides, allantoin and allantoic acid in tropical species. These solutes serve as the principal translocated forms of nitrogen in xylem. Compartmentalisation of the pathways of nitrogen metabolism and the role of ammonia in regulation of their activity is examined in nodules of both asparagine-forming (Lupinus albus L.) and ureide-forming (Vigna unguiculata L. Walp) symbioses.
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    Plant and soil 100 (1987), S. 171-181 
    ISSN: 1573-5036
    Keywords: Co-evolution ; Gene pool ; Nitrogen fixation ; Pisum sativum L. ; Rhizobium leguminosarum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A number of examples is given demonstrating the co-existence of pea genotypes and their specific Rhizobium, strains isolated within the same region.R. leguminosarum strains compatible with the cultivated pea have a narrow symbiotic range and they are widely distributed in European soils. This is presumably due to the narrow genetic base of the cultivated pea and its wide-spread cultivation in European soils. Rhizobium strains capable of nodulating a primitive pea line from Afghanistan were only found in soils of the Middle East and Central Asia. A more restricted distribution of specific Rhizobium strains was found for fulvum peas from Israel. Rhizobium strains effective with the fulvum pea were found in Israeli soils. A good example of co-evolution due to geographical isolation was found in south Turkey. Here a pea line was found which can form an effective symbiosis with local Rhizobium strains but not with strains from other parts of Turkey.
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    Plant and soil 100 (1987), S. 183-212 
    ISSN: 1573-5036
    Keywords: Anabaena azollae ; Azolla ; Desiccation ; Macrosporocarps ; Microsporocarps ; Nitrogen fixation ; Sexual reproduction ; Survival Azolla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The survival of Azolla was studied in an artificial system which simulated the soil/water interface and the desiccation of soil during a fallow period in lowland rice culture. Tests with non-sporulating and sporulating Azolla fronds showed that Azolla only survives with sporulated fronds. At their reappearance the Azolla fronds already harboured the Anabaena endophyte. A detailed light microscopic and transmission electron microscopic study of macro- and micros-porocarp formation and development revealed that the endophyte is transmitted by the macrosporocarps and not by the microsporocarps. The Anabaena cells within the macrosporocarps are found just below the indusium cap. These cells are not nitrogen-fixing akinetes. The free-living Anabaena cells at the stem apex and below the overarching developing leaves do not bear heterocysts and accordingly are non nitrogen-fixing. During the development of the leaf the Anabaena enters the leaf cavity, but later the pore of this, cavity closes and the imprisoned cyanobacteria are lysed before the leaf decays. As the Azolla leaves age a nitrogen-fixing capability is successively built up concomittantly with the production of heterocysts. Heterocyst frequencies of 40–50% can be found inAnabaena azollae. Usually a gradient of nitrogen-fixing capacity occurs along the Azolla rhizome with two distinct peaks at leaf number 7/8 and at leaf number 13/14 from the apex.
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  • 77
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    Plant and soil 100 (1987), S. 225-236 
    ISSN: 1573-5036
    Keywords: Actinorhizae ; Alnus ; Casuarina ; Frankia ; Hemoglobin ; Myrica ; Nitrogen fixation ; Root nodules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The concentration of total and CO-reactive heme was measured in actinorhizal nodules from six different genera. This gave the upper limit to hemoglobin concentration in these nodules. Quantitative extraction of CO-reactive heme was achieved under anaerobic conditions in a buffer equilibrated with CO and containing Triton X-100. The concentration of CO-reactive heme in nodules of Casuarina and Myrica was approximately half of that found in legume nodules, whereas in Comptonia, Alnus and Ceanothus the concentrations of heme were about 10 times lower than in legume nodules. There was no detectable CO-reactive heme in Datisca nodules, but low concentrations were detected in roots of all non-nodulating plants examined, includingZea mays. Difference spectra of CO treated minus dithionite-reduced extracts displayed similar wavelengths of maximal and minimal light absorption for all extracts, and were consistent with those of a hemoglobin. The concentration of CO-reactive heme was not correlated to the degree to which CO inhibited nitrogenase activity nor was it affected by reducing the oxygen concentration in the rooting zone. However, there was a positive correlation between heme concentration and suberization or lignification of the walls of infected host cells. These observations demonstrate that, unlike legume nodules, high concentrations of heme or hemoglobin are not needed for active nitrogen fixation in most actinorhizal nodules. Nonetheless, a significant amount of CO-reactive heme is found in the nodules of Alnus, Comptonia, and Ceanothus, and in the roots ofZea mays. The identity and function of this heme is unknown.
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  • 78
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    Plant and soil 98 (1987), S. 265-274 
    ISSN: 1573-5036
    Keywords: Alfalfa ; Birdsfoot trefoil ; Bromegrass ; Nitrogen fixation ; Nitrogen transfer ; Orchardgrass ; Red clover ; Red fescue ; Tall fescue ; Timothy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Three legume species (alfalfa, red clover, and birdsfoot trefoil) in combination with five grass species (timothy, bromegrass, red fescue, tall fescue, and orchardgrass) were used to study N transfer in mixtures, using the 15N dilution technique. The advantage of grass-legume mixtures was apparent. Total herbage and protein yields of grasses in mixtures were higher than those alone, especially at the later cuts. This benefit of mixed cropping is mainly due to N transfer from legumes to associated grasses. N2-fixation and N transfer by alfalfa rated highest, red clover intermediate, and birdsfoot trefoil lowest. The importance of each pathway of N transfer from legumes appeared to differ between species. Alfalfa and red clover excreted more N than trefoil, while the latter contributed more N from decomposition of dead nodule and root tissue. The greatest advantage from a grass-legume mixture, with respect to the utilization of N released from the legume, varied with early maturing tall fescue (Kentucky 31), orchardgrass (Juno), and bromegrass (Tempo), to intermediate timothy (Climax), and least with late maturing red fescue (Carlawn).
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  • 79
    ISSN: 1573-5036
    Keywords: Cajanus cajan ; Maturity groups ; Nitrogenase activity ; Nitrogen fixation ; Nitrogen uptake ; Nodulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The seasonal patterns of nodulation, acetylene reduction, nitrogen uptake and nitrogen fixation were studies for 11 pigeonpea cultivars belonging to different maturity groups grown on an Alfisol at ICRISAT Center, Patancheru, India. In all cultivars the nodule number and mass increased to a maximum around 60–80 days after sowing and then declined. The nodule number and mass of medium- and late-maturing cultivars was greater than that of early-maturing cultivars. The nitrogenase activity per plant increased to 60 days after sowing and declined thereafter, with little activity at 100 days when the crop was flowering. At later stages of plant growth nodules formed down to 90 cm below the soil surface but those at greater depth appeared less active than those near the surface. All the 11 cultivars continued to accumulate dry matter until 140 days, with most biomass production by the late-maturing cultivars (up to 11 t ha−1) and least by the early-maturing determinate cultivars (4 t ha−1). Total nitrogen uptake ranged from 69 to 134 kg ha−1. Nitrogen fixation by pigeonpea was estimated as the difference in total nitrogen uptake between pigeonpea and sorghum and could amount to 69 kg N ha−1 per season, or half the total nitrogen uptake. Fixation by pigeonpea increased with crop duration, but there were differences within each maturity group. The limitations of the methods used for estimating N2 fixation by pigeonpea are discussed.
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  • 80
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    Plant and soil 99 (1987), S. 285-290 
    ISSN: 1573-5036
    Keywords: Alder ; Actinomyces ; Nodulation ; Nitrogen fixation ; Purplish soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The alder has a perennial nodule cluster. The nodule amount on the roots increases with tree age. The N2-fixing activity of nodules decreases with nodule age. Purple coloured soils with various soil pHs and CaCO3 contents are, in the main, the ones which influence nodulation and N2-fixing. Higher N2-fixing capacity existed in the neutral and low calcium soils. High calcium soils and acid soils can restrain nodulation and the N2-fixing rate significantly. On the slope, where calcarous light loams are found, the annual nitrogen fixation capacity of alder and cypress mixed plantations, less than 10 years old, is 16 or 17 kg/ha yr, but in the valley, a pure alder plantation can reach 40 kg/ha yr.
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  • 81
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    Plant and soil 99 (1987), S. 435-439 
    ISSN: 1573-5036
    Keywords: Cowpea ; Effective nodulation ; Nitrogen fixation ; Nodule growth ; Plant age ; Rhizobium strain ; Vigna unguiculata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Rhizobium strains CIAT 301, CIAT 79 and SLM 602 were tested and found effective in the nodulation and nitrogen fixation of cowpea cv. MI-35 (Vigna unguiculata (L.) Walp) plants in growth chamber experiments. Fresh weight of nodules increased with plant age initially and stabilized in 20–30 days from planting, followed by a secondary flush of nodule growth after 30 days. Apparent nitrogen fixation per gram nodule fresh weight reached a maximum in 20–30 days after planting and then decreased, even though a flush of new nodules was produced.
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  • 82
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    Plant and soil 98 (1987), S. 425-428 
    ISSN: 1573-5036
    Keywords: Diazotrophs ; Ectomycorrhizae ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrogenase activity, measured by acetylene reduction, was detected on nursery-grown, surface-sterilized ectomycorrhizae of Douglas-fir, formed withLaccaria laccata, Hebeloma crustuliniforme, Rhizopogon vinicolor, andThelephora sp. Detached mycorrhizae were incubated in nitrogen-free liquid medium under microaerophilic conditions. Nitrogenase activity was attributed toClostridium spp. andAzospirillum spp.
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  • 83
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Lucerne ; Medicago sativa ; 15N methodology ; Nitrogen fixation ; Quantitative estimation ; Seasonal pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Lucerne is an important forage legume in the south and south-east of Sweden on well-drained soils. However, data is lacking on the apparent amount of nitrogen derived through N2 fixation by field-grown lucerne. This report provides basic information on the subject. The experiment was performed in a lucerne ley grown 40 km north of Uppsala. The input of nitrogen through fixation to the above-ground plant material of an established lucerne (Medicago sativa L.) ley was estimate by15N methodology during two successive years. The amount of fixed N was 242 kg N ha−1 in 1982 and 319 kg N ha−1 in 1983. The proportion of N derived from the atmosphere (%Ndfa) was 70% and 80% for the two years respectively. The first harvest in both years contained a lower proportion fixed N. Both N2 fixation and dry matter production were enhanced during the second year, particularly in the first harvest. The Ndfa was 61% in the first harvest in 1982, compared to 72% Ndfa during the same period in 1983. This demonstrates the strong influence of environment on both dry matter production and N2 fixation capacity of the lucerne. In addition anin situ acetylene reduction assay was used in 1982 to measure the seasonal distribution of the N2 fixation and in 1983 to study the effect of soil moisture on the N2 fixation process. The seasonal pattern showed great dependence on physiological development and harvest pattern of the lucerne ley. The maximum rate of N2 fixation occurred at the bud or early flower stage of growth and was followed by a rapid decline as flowering proceeded. After harvest the nitrogenase activity markedly decreased and remained low during at least two weeks until regrowth of new shoots began. Irrigation doubled the nitrogenase activity of the lucerne in late summer 1983, when soil moisture content in the top soil was near wilting point. No changes in nitrogenase activity did occur in response to watering earlier during the summer, when the soil matric potential was around −0.30 MPa.
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  • 84
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    Plant and soil 90 (1986), S. 141-150 
    ISSN: 1573-5036
    Keywords: Aromatic degradation ; Bacteria ; Nitrogen fixation ; Phenolics ; Physiology ; Soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A microaerobic diazotrophic bacterium tentatively identified as aPseudomonas species was isolated from a forest soil. Its nitrogenase (C2H2 reduction) activity in liquid medium was significantly supported by phenolic compounds when compared with glucose-, mannitol- or malate-supported activity. The utilization of phenolics was dependent on substrate induction and the appropriate oxygen concentration. At a pO2 of 0.05 protocatechuate was a better carbon source for N2 fixation than glucose. In the case ofLignobacter protocatechuate was a better carbon source for N2 fixation than glucose at pO2 0.2 but not at pO2 0.05. It is suggested that certain monomeric phenols can support nitrogenase activities in many carbon-limited soil environments.
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  • 85
    ISSN: 1573-5036
    Keywords: Nitrogen fixation ; Nucleotide pools ; Rhodospirillum rubrum ; Switch off
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary When ammonium ions are added to a nitrogen fixing culture ofRhodospirillum rubrum, nitrogenase activity decreases due to inactivation of the Fe-protein. We have studied the adenylate and pyridine nucleotide pools during switch-off using the sensitive bioluminescence method. Immediately after the addition of ammonium ions there is a decrease in the ATP pool which is quickly reversed and no change is seen during the switch-off period. The pyridine nucleotide pools also do not change significantly during the switch-off. Consequently we conclude that changes in the pools studied were not the signal promoting inactivation of the Fe-protein.
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  • 86
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    Plant and soil 90 (1986), S. 193-202 
    ISSN: 1573-5036
    Keywords: azospirillum ; Denitrification ; Nitrate respiration ; Nitrite reductase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Model experiments were performed to investigate the nitrogen fixation (C2H2 reduction) and denitrification (N2O formation) capabilities ofAzospirillum spp. in association with wheat. Plants and bacteria were grown together for a week and then assayed for activities. This association performed C2H2 reduction or N2O formation, depending on the concentrations of nitrate and oxygen in the vessels. Both activities depended on theAzospirillum strains used. The newly isolatedAzospirillum amazonense strains Y1 and Y6 showed significant C2H2 reduction and low N2O formation in association with wheat under the conditions employed and are possibly useful in practice. A cell-free preparation fromAzospirillum brasilense Sp 7 possessed a cytochrome cd type dissimilatory nitrite reductase.
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  • 87
    ISSN: 1573-5036
    Keywords: Blue grass ; Klebsiella pneumoniae ; Poa pratensis ; Triticum aestivum ; Nitrogen fixation ; Nitrogen nutrition ; 15N isotope dilution ; Spring wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The technique of15N isotope dilution was used to verify that nitrogen was fixed and transferred to the plant byKlebsiella pneumoniae strain Pp in association withPoa pratensis orTriticum aestivum. Surface sterilized, sprouting seeds were inoculated withK. pneumoniae and grown in sand in modified Leonard jars. Potassium nitrate enriched with15N was used to provide N concentrations ranging from 10–40 mg Nl−1 nutrient solution. After 10–18 weeks the shoots and roots were analyzed separately for dry matter, N content, total N, and atom %15N excess. The acetylene reduction technique was used to test for the presence of N2-fixing organisms on the roots. The data from15N isotope dilution demonstrated that up to 33.8% of N in the shoots ofP. pratensis and 15.9% in those ofT. aestivum were derived from associative N2 fixation byK. pneumoniae. In most experiments the dry matter yield, N content, and total N yield of the shoots ofP. pratensis were increased byK. pneumoniae inoculation, whereas inoculation had no significant effect on the dry matter yield, N content or total N of the shoots ofT. aestivum.
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  • 88
    ISSN: 1573-5036
    Keywords: Brachiaria spp ; Nitrogen fixation ; 15N techniques ; Paspalum notatum ; Pasture grasses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Six pasture grasses,Paspalum notatum cv batatais,P. notatum cv pensacola,Brachiaria radicans, B. ruziziensis, B. decumbens andB. humidicola, were grown in concrete cylinders (60 cm diameter) in the field for 31 months. The soil was amended with either a single addition of15N labelled organic matter or frequent small (2 kg N. ha−1) additions of15N enriched (NH4)2SO4. In the labelled fertilizer treatment soil analysis revealed that there was a very drastic change in15N enrichment in plant-available nitrogen (NO 3 − +NH 4 + ) with depth. The different grass cultivars recovered different quantities of applied labelled N, and evidence was obtained to suggest that the roots exploited the soil to different depths thus obtaining different15N enrichments in soil derived N. This invalidated the application of the isotope dilution technique to estimate the contribution of nitrogen fixation to the grass cultivars in this treatment. In the labelled organic matter treatment the15N label in the plant-available N declined at a decreasing rate during the experiment until in the last 12 months the decrease was only from 0.274 to 0.222 atom % excess. There was little change in15N enrichment of available N with depth, hence it was concluded that although the grasses recovered different quantities of labelled N, they all obtained virtually the same15N enrichment in soil derived N. Data from the final harvests of this treatment indicated thatB. humidicola andB. decumbens obtained 30 and 40% respectively of their nitrogen from N2 fixation amounting to an input of 30 and 45 kg N.ha−1 year−1 respectively.
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  • 89
    ISSN: 1573-5036
    Keywords: Azolla caroliniana (Willd.) ; Isotope dilution ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha−1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two15N methods. In the first,Azolla caroliniana (Willd.) was labelled with15N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha−1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of15N-urea was applied separately or in combination with either 250 or 330 kg N ha−1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha−1 to 430 kg N ha−1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using15N-labelledAzolla, this method is preferable to the15N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at −20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla.
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  • 90
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    Plant and soil 90 (1986), S. 335-342 
    ISSN: 1573-5036
    Keywords: Azospirillum brasilense ; Effect on yield ; Inoculation ; Legumes ; Nitrogen fixation ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Inoculation of naturally nodulatedPisum sativum L. (garden pea) withAzospirillum in the greenhouse caused a significant increase in nodule numbers above controls. Field inoculation of garden peas in the winter 1981–1982 andCicer arietinum L. (chick pea), in winter 1982–1983, withAzospirillum one week after plant emergence, produced a significant increase in seed yield, but did not affect plant dry matter yield. ForVicia sativa L. (vetch) grown in soil in the greenhouse and in the field for forage, winter 1980–1981, inoculation significantly increased dry matter yield, %N, N-content, and acetylene reduction (nitrogen fixation) activity. InHedysarum coronarium L. (sulla clover), winter 1981–1982, inoculated with both its specificRhizobium (by the slurry method) andAzospirillum, 7 days after emergence, there was an increase in acetylene reduction above controls inoculated withRhizobium alone. These results suggest that it is possible, under conditions tested in this work, to increase nodulation, nitrogen fixation, and crop yields of winter legumes by inoculation withAzospirillum.
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  • 91
    ISSN: 1573-5036
    Keywords: Alnus rubra ; Alnus glutinosa ; Fatty acids ; Frankia ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Alnus species are used widely in Britain for land reclamation, forestry and other purposes. Rapid juvenile growth of the AmericanAlnus rubra makes it an attractive species for planting on N-deficient soils, particularly those of low organic content. In small plot trials, this species is nodulated by indigenous soil frankiae as effectively asAlnus glutinosa. Over a three year period both species return similar amounts of N to the ecosystem, estimated at up to 10–12 kg N ha−1. Several strains ofFrankia have been isolated from local (Lennox Forest)A. rubra nodules. These differ morphologically and in their growth on different culture media, both from each other and fromA. glutinosa nodule isolates. AllAlnus isolates, however, have a total cellular fatty acid composition qualitatively similar to some other Group B frankiae. Glasshouse tests in N free culture suggest thatA. rubra nodules formed after inoculation of seedlings with American spore (−) isolates are three times more effective in N fixation than those inoculated with LennoxA. rubra spore (+) nodule homogenates. By contrast, the early growth of seedlings inoculated with spore (−)Frankia strains suggests at best a 35% improvement in N fixing activity over seedlings inoculated with LennoxA. rubra nodule isolates. Nevertheless, this improvement in activity, together with the better performance of seedlings inoculated with isolates compared with those treated with crushed nodule preparations, suggest that it would be worthwhile commercially to inoculate nursery stock with a spore (−)Frankia strain.
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  • 92
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    Plant and soil 90 (1986), S. 429-453 
    ISSN: 1573-5036
    Keywords: Actinorhizae ; Frankia ; Genetics ; Nitrogen fixation ; Nodulation ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 93
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    Plant and soil 91 (1986), S. 43-49 
    ISSN: 1573-5036
    Keywords: Alnus incana ; Frankia ; Leaf litter ; Nitrogen fertilization ; Nitrogen fixation ; Root exudation ; Root litter ; Shoot litter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A pot experiment withAlnus incana (L.) Moench growing in sand was set up to compare the amounts of nitrogen released from plants shoot litter with that released below ground as root litter and/or root exudation. No nitrogen fixation by free-living microorganisms was found in the sand and the increased nitrogen content of the plant + soil system was therefore due to nitrogen fixation byFrankia in the alder root-nodules. Most of the nitrogen released from the plants was in the nitrogen-rich leaf and other shoot litter. Only small amounts of nitrogen were found in the drainage water from the pots and were recorded as increased nitrogen content of the sand.
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  • 94
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    Plant and soil 91 (1986), S. 147-160 
    ISSN: 1573-5036
    Keywords: Cowania ; Frankia ; Microbial ecology ; Nitrogen fixation ; Purshia ; Revegetation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Nitrogen fixing trees and shrubs may be useful in revegetation efforts. The possibility that soil and environmental factors may influence a soil's capability to produce nodulated seedlings was explored.Purshia tridentata andCowania mexicana var. Stansburiana seedlings were grown in greenhouse trials using ten soils from native sites for each of the two genera. Treatments included a control and a six mmole nitrogen amendment as NH4NO3 for both surface and subsurface samples. Nodulation was often sparse for seedlings grown in surface collected samples. Although nodulation was usually better in subsoil samples, even some subsoils produced few or no nodules. Nitrogen additions inhibit nodulation and although soil nitrogen may be inhibitory in some unamended surface soils it is probably not a general cause of sparse nodulation. Nodule masses showed the same trends as nodule number but varied less with treatment and depth of soil source. Seedlings compensated for sparse nodulation with an increase in mass per nodule. Incidence of nodulation was related to some soil and environmental factors. Multiple regression analysis explained a substantial portion of nodulation variability. Soils from lower elevations with less precipitation did not produce well nodulated seedlings even in well watered greenhouse trials. Micronutrient cations, potassium, and phosphorus are positively correlated with nodulation incidence. The two genera were generally similar in nodulation responses to soil and environmental factors.
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  • 95
    ISSN: 1573-5036
    Keywords: A-value ; Barley ; Field bean ; Isotope dilution ; Nitrogen fixation ; 15N ; Non-fixing reference crop ; Pea ; Pisum sativum ; Vicia faba
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The total amount of nitrogen derived from symbiotic nitrogen fixation in two pea and one field bean cultivar, supplied with 50 kg N ha−1 at sowing (‘starter’-N), was estimated to 165, 136, and 186 kg N ha−1, respectively (three-year means). However, estimates varied considerably between the three years. At the full bloom/flat pod growth stage from 30 to 59 per cent of total N2 fixation had taken place. The proportion of total N derived from N2 fixation at maturity was higher in seeds than in vegetative plant parts and amounted to 59.5, 51.3 and 66.3 per cent of total above-ground plant N in the two pea cultivars and field bean, respectively (three-year means). The recovery of fertilizer N was 62.2, 70.2, 52.1, and 69.5 per cent in the two pea cultivars, field bean and barley, respectively. Growth analysis indicated that barley did not meet the claims for an ideal reference crop in the15N fertilizer dilution technique for estimating N2 fixation in pea and field bean. ‘Starter’-N neither increased the seed yield nor the N content of the grain legumes.
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  • 96
    ISSN: 1573-5036
    Keywords: Mycorrhiza ; Nitrogen fixation ; Nodulation ; Soybean ; Symbioses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Glycine max (L. Merr. cv. Amsoy 71) plants were grown in a greenhouse in a sand/perlite medium low in plant-available N and P. Plants were either inoculated with a vesicular-arbuscular mycorrhizal (VAM) fungus alone, a strain ofRhizobium japonicum alone, both endophytes together or were left non-inoculated to serve as a control. All combinations received a N-and P-free nutrient solution. Nodulated plants contained 4 to 5 times the phytomass of non-inoculated controls, and plants colonized with both the VAM fungus and Rhizobium were 18% greater in dry weight than nodulated, non-VAM plants due to a positive VAM times Rhizobium interaction. Nitrogen fixation, calculated from C2H4 and H2 data, was significantly higher in the tripartite symbiosis, with 80% of the increase attributable to increased nodule mass and 20% due to increases in specific nodule activity. Colonization by the VAM fungus and the development of vesicles increased significantly following nodulation. The synergistic interactions between the microsymbionts suggests that the response of the host to dual colonization is complex and depends on a balance between the three members of the symbiosis.
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  • 97
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    Plant and soil 92 (1986), S. 55-62 
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Environmental factors ; Low temperature ; Nitrogen fixation ; Rhizobium ; Trifolium pratense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Red clover Rhizobium strains, isolated from different locations between latitudes 60° and 63°30′ N in Finland, were tested for their adaptation to low temperatures. 31 strains were tested for growth at 5°C, 10°C, 15°C and 18°C in pure culture. No strain grew at 5°C. At the other temperatures there were differences between the strains, but the same strains grew fast at all temperatures. Ten strains were investigated for nodulation and acetylene reduction in phytotrons in two different climates, one simulating the growing season in southern and the other in northern Finland. There were differences between the strains in their ability to nodulate their host plant, and northern strains showed higher nitrogenase activity than southern strains in the cold climate.
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  • 98
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    Plant and soil 92 (1986), S. 171-180 
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Associative nitrogen fixation ; Azospirillum ; Nitrogen fixation ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Spring-wheat plant seedlings were inoculated with various isolates of nitrogen-fixing rhizosphere bacteria, includingAzospirillum brasilense, in gnotobiotic sand cultures. Bacteria which had lost their acetylene reduction activity (ARA) during purification did not regain it in the presence of the plant. Bacteria with stable ARA were stimulated to low ARA (maximum 5.6 nmol C2H4 plant−1 h−1) by young (22–32-day) wheat seedlings.
    Type of Medium: Electronic Resource
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  • 99
    ISSN: 1573-5036
    Keywords: Cowpea ; Nitrogen fixation ; Nodulation ; Pea ; Pesticide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Six carbamate pesticides namely 1-naphthol, sevin, dimetilan, trematan, NaDDC and dymid were studied to see their effect on nodulation and nitrogen fixation inPisum sativum andVigna sinensis. Low concentrations of the pesticides have little effect on nodulation and nitrogen fixation, whereas higher concentrations adversely effect these processes. The results also indicate that then sensitivity depends upon the species of the Rhizobium and also the type of the pesticide. Pesticides belonging to the carbamate group differ in their capacity to affect nodulation and nitroge fixation.
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 95 (1986), S. 301-313 
    ISSN: 1573-5036
    Keywords: Alnus glutinosa ; Ammonium ; Nitrate ; Nitrate reductase activity ; Nitrogen fixation ; Phyllosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Thein vivo nitrate reductase activity (NRA) was determined inAlnus glutinosa plants grown nonsymbiotically on ammonium, nitrate, a combination of both, or symbiotically with atmospheric nitrogen as the only nitrogen source. Root NRA was absent when ammonium or atmospheric nitrogen was the nitrogen source. With nitrate in the culture solution the roots showed a high NRA. However, the leaf NRA behaved quite differently: with negligible activities on all nitrogen sources except atmospheric nitrogen. The foliar NRA measured, however, is likely not due to the activity of the plant but of microbial origin. Methods commonly used to facilitate produced nitrite to leak out of the tissue, such as addition of propanol and cutting the plant material, did not increase the nitrite release from the leaves. A turbidity developed when testing the samples for nitrite which was positively correlated with the NRA. Populations of microorganisms in the phyllosphere did not differ between the nutritional treatments. Bacteria, able to grow on a low-nitrogen medium, were present on the leaves. Nitrifiers could not be detected. The bacteria on the leaves appear to produce nitrite when incubated with leaf material.
    Type of Medium: Electronic Resource
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