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Protease and deaminase activities in wheat rhizosphere and their relation to bacterial and protozoan populations (1996)

Badalucco, L. ; Kuikman, P. J. ; Nannipleri, P.

Springer

Biology and fertility of soils 23 (1996), S. 99-104

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ISSN: 1432-0789

Keywords: Rhizosphere effect ; Protease activity ; Deaminase activity ; Bacteria ; Protozoa ; Nitrogen mineralization

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Protease and deaminase activities and population dynamics of bacteria and protozoa were measured in the rhizosphere of wheat to study their interactions with the mineralization of nitrogen. The experimental design allowed the separation of roots and soil material by means of a gauze. The most pronounced “rhizosphere effect” was detected for all the measured variables in the soil closest to the gauze. The number of bacteria was significantly higher in the presence than in the absence of plants up to 4 mm away from the soil-root interface and the closer to this interface the higher the number. Protozoan and bacterial population dynamics were positively correlated; generally, populations of flagellates and amoebae were comparable and their sum accounted for the population of total protozoa. For both enzyme activities the rhizosphere effect extended up to 2 mm away from the soil-root interface. The histidinase activity was of bacterial origin, while it is likely that bacteria, protozoa and root hair all contributed to the overall caseinase activity. Decomposition of root exudates and native organic matter in the rhizosphere, reflected by a growing microbial population, is associated with nitrogen mineralization through increases in caseinhydrolysing and L-histidine-deaminating activities. The adopted soil-plant microcosm is suitable for the study of the rhizosphere effect over time of incubation and distance gradient from the soil-root interface.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00336047

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Protease and deaminase activities in wheat rhizosphere and their relation to bacterial and protozoan populations (1996)

Badalucco, L. ; Kuikman, P. J. ; Nannipieri, P.

Springer

Biology and fertility of soils 23 (1996), S. 99-104

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ISSN: 1432-0789

Keywords: Key words Rhizosphere effect ; Protease activity ; Deaminase activity ; Bacteria ; Protozoa ; Nitrogen mineralization

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Protease and deaminase activities and population dynamics of bacteria and protozoa were measured in the rhizosphere of wheat to study their interactions with the mineralization of nitrogen. The experimental design allowed the separation of roots and soil material by means of a gauze. The most pronounced „rhizosphere effect” was detected for all the measured variables in the soil closest to the gauze. The number of bacteria was significantly higher in the presence than in the absence of plants up to 4mm away from the soil-root interface and the closer to this interface the higher the number. Protozoan and bacterial population dynamics were positively correlated; generally, populations of flagellates and amoebae were comparable and their sum accounted for the population of total protozoa. For both enzyme activities the rhizosphere effect extended up to 2mm away from the soil-root interface. The histidinase activity was of bacterial origin, while it is likely that bacteria, protozoa and root hair all contributed to the overall caseinase activity. Decomposition of root exudates and native organic matter in the rhizosphere, reflected by a growing microbial population, is associated with nitrogen mineralization through increases in casein-hydrolysing and l-histidine-deaminating activities. The adopted soil-plant microcosm is suitable for the study of the rhizosphere effect over time of incubation and distance gradient from the soil-root interface.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00336047

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3

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The impact of protozoa on the availability of bacterial nitrogen to plants (1989)

Kuikman, P. J. ; Veen, J. A.

Springer

Biology and fertility of soils 8 (1989), S. 13-18

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ISSN: 1432-0789

Keywords: Bacteria ; Protozoa ; Predation ; Nitrogen ; Mineralization ; Plant uptake ; Soil

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary Microbial N from 15N-labelled bacterial biomass was investigated in a microcosm experiment, in order to determine its availability to wheat plants. Sterilized soil was inoculated with either bacteria (Pseudomonas aeruginosa alone or with a suspension of a natural bacterial population from the soil) or bacteria and protozoa to examine the impact of protozoa. Plant biomass, plant N, soil inorganic N and bacterial and protozoan numbers were determined after 14 and 35 days of incubation. The protozoa reduced bacterial numbers in soil by a factor of 8, and higher contents of soil inorganic N were found in their presence. Plant uptake of N increased by 20010 in the presence of protozoa. Even though the total plant biomass production was not affected, the shoot: root ratios increased in the presence of protozoa, which is considered to indicate an improved plant nutrient supply. The presence of protozoa resulted in a 65010 increase in mineralization and uptake of bacterial 15N by plants. This effect was more pronounced than the protozoan effect on N derived from soil organic matter. It is concluded that grazing by protozoa strongly stimulates the mineralization and turnover of bacterial N. The mineralization of soil organic N was also shown to be promoted by protozoa.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00260510

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Protozoan predation and the turnover of soil organic carbon and nitrogen in the presence of plants (1990)

Kuikman, P. J. ; Jansen, A. G. ; Veen, J. A. ; [et al.]

Springer

Biology and fertility of soils 10 (1990), S. 22-28

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ISSN: 1432-0789

Keywords: Protozoan grazing ; Organic carbon turnover ; Microbial activity ; Nitrogen mineralization ; Microcosm ; Microbial biomass

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Summary The impact of protozoan grazing on the dynamics and mineralization of 14C- and 15N-labelled soil organic material was investigated in a microcosm experiment. Sterilized soil was planted with wheat and either inoculated with bacteria alone or with bacteria and protozoa or with bacteria and a 1:10 diluted protozoan inoculum. 14C−CO2 formation was continuously monitored. It served as an indicator of microbial activity and the respiration of soil organic C. The activity of protozoa increased the turnover of 14C-labelled substrates compared to soil without protozoa. The accumulated 14C−CO2 evolved from the soils with protozoa was 36% and 53% higher for a 1:10 and for a 1:1 protozoan inoculum, respectively. Protozoa reduced the number of bacteria by a factor of 2. In the presence of protozoa, N uptake by plants increased by 9% and 17% for a 1:10 and a 1:1 protozoan inoculum, respectively. Both plant dry matter production and shoot: root ratios were higher in the presence of protozoa. The constant ratio of 15N: 14+15N in the plants for all treatments indicated that in the presence of protozoa more soil organic matter was mineralized. Bacteria and protozoa responded very rapidly to the addition of water to the microcosms. The rewetting response in terms of the 14C−CO2 respiration rate was significantly higher for 1 day in the absence and for 2 days in the presence of protozoa after the microcosms had been watered. It was concluded that protozoa improved the mineralization of N from soil organic matter by stimulating the turnover of bacterial biomass. Pulsed events like the addition of water seem to have a significant impact on the dynamics of food-chain reactions in soil in terms of C and N mineralization.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00336120

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ESPAS — An advanced phytotron for measuring carbon dynamics in a whole plant-soil system (1996)

Gorissen, A. ; Kuikman, P. J. ; Ginkel, J. H. ; [et al.]

Springer

Plant and soil 179 (1996), S. 81-87

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ISSN: 1573-5036

Keywords: carbon allocation ; phytotron ; pulse-labelling ; steady-state labelling ; 13C ; 14C

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The use of carbon isotopes as tracers is essential for measuring carbon flows in an intact whole plant-soil system. Here, we describe and Experimental Soil Plant Atmosphere System (ESPAS) to perform pulse-labelling and steady-state labelling experiments with 13CO2 and 14CO2. The ESPAS facility is an environmental research tool that is used to measure the carbon fluxes from the atmosphere to the roots and into the soil and the microbial biomass and to study decomposition of plant residues and soil organic matter. The influence of environmental conditions in the atmosphere or in soil on the carbon allocation and turnover in the plant-soil ecosystem can be quantified. The design and the technical description of the phytotrons is presented and evidence is provided that the phytotrons are equivalent. For this purpose, Triticum aestivum plants were cultivated in the phytotrons for 39 days and shoot growth, root growth and water use were compared. No significant differences were observed for plant growth and water use. As an example of the practical application of the equipment, an experiment with elevated atmospheric CO2 is presented. Data are given on the uptake of 14C under ambient (350 μL L−1) and elevated (700 μL L−1CO2) in Lolium perenne and Festuca arundinacea and the distribution of 14C among different plant-soil compartments i.e. shoot, root, root-soil respiration, and soil. We conclude that these phytotrons yield detailed information on gross carbon flows in a whole plant-soil system that can not be obtained without sensitive carbon tracers. Such data are important for proper calibration of simulation models on soil organic matter.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00011645

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6

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Soil structural aspects of decomposition of organic matter by micro-organisms (1990)

Veen, J. A. ; Kuikman, P. J.

Springer

Biodegradation 11 (1990), S. 213-233

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ISSN: 1572-9729

Keywords: Decomposition ; microbial biomass ; soil architecture ; soil organic matter ; 15N ; 14C

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Soil architecture is the dominant control over microbially mediated decomposition processes in terrestrial ecosystems. Organic matter is physically protected in soil so that large amounts of well-decomposable compounds can be found in the vicinity of largely starving microbial populations. Among the mechanisms proposed to explain the phenomena of physical protection in soil are adsorption of organics on inorganic clay surfaces and entrapment of materials in aggregates or in places inaccessible to microbes. Indirect evidence for the existence of physical protection in soil is provided by the occurrence of a burst of microbial activity and related increased decomposition rates following disruption of soil structures, either by natural processes such as the remoistening of a dried soil or by human activities such as ploughing. In contrast, soil compaction has only little effect on the transformation of 14C-glucose. Another mechanism of control by soil structure and texture on decomposition in terrestrial ecosystems is through their impact on microbial turnover processes. The microbial population is not only the main biological agent of decomposition in soil, it is also an important, albeit small, pool through which most of the organic matter in soil passes. Estimates on the relative importance of different mechanisms controlling decomposition in soil could be derived from results of combined tracer and modelling studies. However, suitable methodology to quantify the relation between soil structure and biological processes as a function of different types and conditions of soils is still lacking.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00004497

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