| 1. |
- Schnürer, Johan, 1957-, et al.
(författare)
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Mineralization of nitrogen from15N labelled fungi, soil microbial biomass and roots and its uptake by barley plants
- 1987
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Ingår i: Plant and Soil. - Dordrecht, Netherlands : Kluwer Academic Publishers. - 0032-079X .- 1573-5036. ; 102:1, s. 71-78
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Tidskriftsartikel (refereegranskat)abstract
- The availability of nitrogen in15N labelled fungi, soil microbial biomass (Ca(15NO3)2 immobilized by addition of glucose), barley roots and Ca(NO3)2 to barley plants was investigated in a greenhouse experiment. Samples of above-ground plant biomass were taken five times during 76 days. During this time, and at the start of the experiment, the C and N contents of the soil microbial biomass were determined. Microbial biomass-C decreased during the first 41 days, and then increased back to pre-treatment levels. Only 2% of the total soil15N was found in the microbial biomass two days after additions of Ca(15NO3)2. At the final sampling 76 days later, 17% of the15N remaining in soil was found in the microbial biomass. In the other tratments, microbial biomass-N accounted for 20% of remaining soil15N in the one that had received fungi, 29% in the one with barley roots and 35% in the Ca(NO3)2 plus glucose treatment. At harvest, 38% of the soil15N at day 0 added as Ca(NO3)2-N, 29% of fungal-N, 10% of N immobilized in the soil microbial biomass and 7% of N in barley roots was recovered in the above-ground plant biomass.It can be concluded that nitrogen in the native soil biomass is resistant to mineralization and plant uptake. The use of laboratory grown organisms for mineralization studies will overestimate the plant availability of nitrogen in soil microorganisms.
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| 2. |
- Bonde, Torben A., et al.
(författare)
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Microbial biomass as a fraction of potentially mineralizable nitrogen in soils from long-term field experiments
- 1988
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 20:4, s. 447-452
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Tidskriftsartikel (refereegranskat)abstract
- Aerobic long-term incubations (40-wk) were employed to measure the potentially mineralizable nitrogen (N0) in five 30-yr old cropping systems. The cropping systems consisted of: (1) bare fallow; (2) cropping with no additions; (3) cropping with 80 kg N ha-1 y-1 as Ca(NO3)2; (4) cropping with 80 kg N ha-1 yr-1 as Ca(NO3)2 plus 1800kg C ha-1 yr-1 as straw; and (5) cropping with 80 kg N ha-1 yr-1 plus 1800 kg C ha-1 yr-1 as farmyard manure. The amounts of N mineralized during the 40-wk incubations were between 93 and 168 μg g-1 (302-543 kg N ha-1 down to 25cm depth) with the lowest value for the fallow and the highest for the farmyard manure treatment. Microbial biomass-C and -N were measured on four occasions during the incubations. The biomass-C showed a rapid decrease to week 4 (to 36% of the initial mass), a slower decrease to week 9 (to 23% of initial mass) and a very slow decline to the final determination at the end of the incubation (to 8% of initial mass). The biomass-N displayed a similar pattern. Two related models were employed to describe the kinetics of N-mineralization during incubation: (1) a two-component first-order; and (2) a simplified special case of the two-component model. In all cases except the straw-amended soil, the simplified two-component model offered the best description of the curves of accumulated mineral-N. The available fraction, Na, of soil organic-N had mineralization rate constants similar to those for mineralization of microbial biomass.
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| 3. |
- Klemendtsson, Leif, et al.
(författare)
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Microbial nitrogen transformations in the root environment of barley
- 1987
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 19:5, s. 551-558
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Tidskriftsartikel (refereegranskat)abstract
- To determine the influence of barley roots on microorganisms and N-transfonning processes in soil, numbers of nitrifiers and potential nitrification and denitrification rates were measured every week for 5 wks. The barley plants were grown in growth chambers in which the root-containing soil layer (A) was separated from three outer soil layers (B, C, D). The numbers and biomass of bacteria, numbers of flagellates and amoebae, total and FDA-active hyphal lengths, microbial biomass carbon and respiration were also determined.The numbers of ammonium oxidizers were positively correlated with root biomass but did not differ significantly between soil layers. Potential ammonium oxidation was stimulated in the root-layer, while potential nitrite oxidation was stimulated in the B- and C-layers.The denitrification activity (measured anaerobically in the presence of excess No- 3) was positively correlated with root biomass in the A-layer. Denitrification activity in the B-layer was positively correlated with the water content of the soil. When roots grew near the nets separating the root layer from the other layers, denitrification activity was stimulated in the next layer (B).We propose that nitrite oxidation in the root zone partly depends on the reduction of nitrate. This would explain why nitrite-oxidizer numbers were usually several orders of magnitude higher than ammonium-oxidizer numbers.Bacterial numbers decreased between wks 1 and 5. Increases in bacteria, naked amoebae and flagellates in all layers between wks 2 and 3 indicated that bacteria were produced until wk 3. There were no signs of bacterial production after wk 3.The total length of hyphae and the length of FDA-active hyphae were not significantly different between layers. However, both of these parameters, as well as total microbial biomass carbon and respiration, were consistently highest in the A-layer.
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| 4. |
- Paustian, Keith, et al.
(författare)
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Fungal growth response to carbon and nitrogen limitation : A theoretical model
- 1987
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 19:5, s. 613-620
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Tidskriftsartikel (refereegranskat)abstract
- A model of fungal growth in soil is described. Two biomass components, cell walls and cytoplasm are considered. Allocation of assimilates to cell wall and cytoplasm synthesis and the relative rate of cytoplasm translocation vary according to C and N availabilities.Model behaviour in relation to substrate supply is examined. For single substrate additions, active mycelium (cytoplasm-filled hyphae) shows a positive correlation to substrate availability, while total hyphal length (cytoplasm-filled + evacuated hyphae) shows an inverse response. For continuous substrate additions, the model predicts that equilibrium levels of active mycelium depend primarily on substrate input rate and yield efficiency and are independent of other parameters controlling substrate availability.Model assumptions about biosynthate allocation and cytoplasm translocation influence N mineralization and immobilization patterns. The model suggests that critical C:N ratios change during decomposition as the fungal biomass develops. The advantages conferred by the mycclial growth form, in terms of conserving energy and nutrient elements in resource-poor environments, are discussed.
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| 5. |
- Paustian, Keith, et al.
(författare)
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Fungal growth response to carbon and nitrogen limitation : Application of a model to laboratory and field data
- 1987
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 19:5, s. 621-629
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Tidskriftsartikel (refereegranskat)abstract
- We evaluated assumptions about fungal growth regulation by applying a model to laboratory and field experimental data. Hyphal length, dry weight, CO2, solution N and solution C were measured during 140 h incubations in liquid batch cultures of Trichoderma harzianum on mineral media at three nitrogen concentrations. Assuming preferential allocation of N to maintain hyphal extension and including cytoplasm translocation gave the best agreement between model predictions and observed data for N-limited growth. When excluding translocation from the model, hyphal length increase could not be well predicted.Fungal growth in an arable soil was simulated for two soil moisture regimes; one receiving rainfall only and one maintained in a moist condition by daily irrigation. Simulations were compared to measured total hyphal length, FDA-active hyphae and O2-consumption. Model results suggested that hyphal length increases were highly subsidized by translocation of cytoplasm. The response of the active biomass component to soil moisture conditions primarily influenced substrate availability.
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| 6. |
- Robertson, Kerstin, et al.
(författare)
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Microbial biomass in relation to C and N mineralization during laboratory incubations
- 1988
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 20:3, s. 281-286
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Tidskriftsartikel (refereegranskat)abstract
- Net carbon and nitrogen mineralization rates were determined for an arable soil during 12 weeks at 37†C using an aerobic incubation-leaching technique. The amounts of mineralized C and N were compared to changes in the contents of C and N in microbial biomass (as determined by the chloroform fumigation incubation method; CFIM) during the incubation and to amounts of organic C and N in the leachates. Microorganisms were also followed by direct counting of bacteria, measurements of total hyphal lengths and fluorescein diacetate (FDA)-active hyphae, and by most probable number determinations of protozoa (naked amoebae and flagellates).Numbers of naked amoebae increased nearly 10-fold initially and then decreased between weeks 6 and 12. Bacterial numbers and FDA-active hyphae decreased during the incubation, and the relative composition changed slightly in favour of bacteria. Total hyphal lengths remained almost constant.A total of 105 μg N g'- soil dry wt and 1179 μg C g- soil dry wt was mineralized during the incubation, while the microbial N pool decreased by 42 γm- soil dry wt and the microbial C pool decreased by 225μ g- soil dry wt. Soluble organic matter in the leachates amounted to 16 and 31% of mineralized C and N, respectively.The possibility of measuring C mineralization with less frequent teachings and determinations of N mineralization offers an easy method for assessing changes in labile soil organic matter over time or for comparisons between soils. Through the use of appropriate C-to-N ratios, the N-content in the labile pool can be calculated.
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| 7. |
- Schnürer, Johan, 1957-, et al.
(författare)
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Fungi, bacteria and protozoa in soil from four arable cropping systems
- 1986
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Ingår i: Biology and Fertility of Soils. - New York : Springer. - 0178-2762 .- 1432-0789. ; 2:3, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- The effects of four cropping systems on soil microorganisms were investigated during 3 years. The cropping systems were B0, barley without nitrogen fertilizers; B120, barley with 120 kg N ha-1 year-1; GL, grass ley receiving 200 kg N ha-1 year-1; and LL, lucerne ley without nitrogen fertilizer additions. At samplings in September during three consecutive years no differences were found between treatments. Total fungal lengths ranged between 0.7 and 2.0 × 103 m and bacterial numbers between 3.5 and 7.2 × 109 g-1 dry wt. soil.Twenty samplings over 3 years in B120 and in GL indicated higher numbers of bacteria and protozoa during the growing season, except for periods with moisture stress. No clear seasonal trends were found for the fungi. When comparing mean values for the 20 samplings, the grass ley contained significantly (P < 0.05) higher numbers of amoebae. Means of the bacterial numbers and biomass, total and FDA-active hyphal lengths were also higher or equal (FDA-active hyphae) but not significantly so.Seventy-nine per cent of the bacterial biomass and 73% of the total fungal lengths were found in the top soil, where also 85% of the oxygen was consumed.
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| 8. |
- Schnürer, Johan, 1957-, et al.
(författare)
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Microbial biomass and activity in an agricultural soil with different organic matter contents
- 1985
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 17:5, s. 611-618
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Tidskriftsartikel (refereegranskat)abstract
- Changes in soil fertility caused by various organic and N-fertilizer amendments were studied in a long-term field trial mostly cropped with cereals. Five treatments were included: (I) fallow, (II) cropping with no C or N addition, (III) cropping with N-fertilization (80 kg ha -1 yr-1), (IV) cropping with straw incorporation (1800kg Cha-1 yr-1) and N-fertilization (80 kg ha-1yr-1), and (V) cropping with addition of farmyard manure (80 kg N + 1800kg Cha-1yr-1). The treatments resulted in soil organic matter contents ranging from 4.3% (I) to 5.8% (V). Microbial biomass and activity were determined by chloroform fumigation, direct counting of fungi (fluorescein diacetate (FDA)-staining and Jones-Mollison agar-film technique) and bacteria (acridine orange staining), most probable number determinations of protozoa, esterase activity (total FDA hydrolysis) and respiration. Both biomass estimates and activity measurements showed a highly significant correlation with soil organic matter. Microbial biomass C ranged from 230 to 600 μg C g-1 dry wt soil, as determined by the fumigation technique, while conversions from direct counts gave a range from 380 to 2260 μg C. Mean hyphal diameters and mean bacterial cell volumes decreased with decreasing soil organic matter content.
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