Adenylates in the soil microbial biomass at different temperatures

Five soils from temperate sites (Germany; 2 arable and 3 grassland) were incubated aerobically at 5, 10, 15, 20, 25, 35, and 40 °C for 8 days. Soils were analysed for soil microbial biomass C, biomass N, AMP, ADP, and ATP to determine whether the increase in the ATP-to-microbial biomass C ratio with increasing temperature was either due to an increase in the adenylate energy charge (AEC) or de novo synthesis of ATP, or both. Around 80% of the variance in microbial biomass C and biomass N was explained by differences in soil properties, only 7% by the temperature treatments. Averaging the data of all 5 soils for each incubation temperature, the microbial biomass C content decreased with increasing temperature from 15 to 40 °C continuously by 2.5 μg g⁻¹ soil °C⁻¹ after 8-days' incubation. However, this decrease was not accompanied by a similar decrease in microbial biomass N. The average microbial biomass C/N ratio was 6.8. Between 54 and 76% of the variance in AMP, ADP, ATP and the sum of adenylates was explained by differences in soil properties and between 14 (ADP) and 27% (ATP) by the temperature treatments. However, temperature effects on AMP and ADP were variable and inconsistent. In contrast, ATP and consequently also the sum of adenylates increased continuously from 5 to 30 °C followed by a decline to 40 °C. The AEC showed similarly a small, but significant increase with increasing temperature from 0.73 to 0.85 at 30 °C. Consequently, the majority of the variance, i.e. roughly 60% in AEC values, but also in ATP-to-microbial biomass C ratios was explained by the incubation temperature. The mean ATP-to-microbial biomass C ratio increased from 4.7 μmol g⁻¹ at 5 °C to a 2.5 fold maximum of 12.0 μmol g⁻¹ at 35 °C. This increase was linear with a rate of 0.26 μmol ATP g⁻¹ microbial biomass C °C⁻¹. The energy for the extra ATP produced during temperature increase is probably derived from an accelerated turnover of endocellular C reserves in the microbial biomass.     

Microbial reaction in activity, biomass, and community structure after long-term continuous mixing of a grassland soil

Long-term continuous mixing at 40% water holding capacity (WHC) or as slurry at 400% WHC should result in increased soil organic matter decomposition rates in comparison to a control treatment at 40% WHC, but may have strong impacts on soil microbial indices for activity, biomass, and community structure. The amount of extractable inorganic N (NO₃-N+NH₄-N) accumulated in the soil solution after 40 weeks of incubation at 25 °C was 3% of total N in the control treatment and 4% in the two continuous mixing treatments. However, in the treatment mixing at 40% WHC, this 33% increase compared to the control treatment might be explained solely by the decrease in microbial biomass N. In the control treatment, microbial indices decreased in the order microbial biomass C (−10%), microbial biomass N (−40%), ergosterol (−45%) and ATP (−60%). In the treatment mixing at 40% WHC, all four microbial biomass indices were significantly lower than the respective index in the control treatment. This was especially true for microbial biomass N. In the treatment mixing as slurry, only the contents of microbial biomass C and ATP were significantly lower in comparison to the control treatment. The correspondence analysis ordination biplot of the phospholipid fatty acid (PLFA) profiles showed distinct clusters for the three treatments at the end of the incubation. The strongest relative decline of 64% was observed for the fungi-specific PLFA 18:3ω6 in the treatment mixing as slurry in comparison to the control treatment. The content of total bacterial PLFA decreased only by 23%. The differences between the control treatment and the treatment mixing at 40% WHC were less apparent. Fungi represent on average 21% of total microbial biomass C at the end of the incubation if the ergosterol content is recalculated into fungal biomass C. In accordance with this percentage, 22% of the group-specific PLFA could be attributed to fungi.     

Shifts in amino sugar and ergosterol contents after addition of sucrose and cellulose to soil

An incubation experiment with organic soil amendments was carried out with the aim to determine whether formation and use of microbial tissue (biomass and residues) could be monitored by measuring glucosamine and muramic acid. Living fungal tissue was additionally determined by the cell-membrane component ergosterol. The organic amendments were fibrous maize cellulose and sugarcane sucrose adjusted to the same C/N ratio of 15. In a subsequent step, spherical cellulose was added without N to determine whether the microbial residues formed initially were preferentially decomposed. In the non-amended control treatment, ergosterol remained constant at 0.44 μg g⁻¹ soil throughout the 67-day incubation. It increased to a highest value of 1.9 μg g⁻¹ soil at day 5 in the sucrose treatment and to 5.0 μg g⁻¹ soil at day 33 in the fibrous cellulose treatment. Then, the ergosterol content declined again. The addition of spherical cellulose had no further significant effects on the ergosterol content in these two treatments. The non-amended control treatment contained 48 μg muramic acid and 650 μg glucosamine g⁻¹ soil at day 5. During incubation, these contents decreased by 17% and 19%, respectively. A 33% increase in muramic acid and an 8% increase in glucosamine were observed after adding sucrose. Consequently, the ratio of fungal C to bacterial C based on bacterial muramic acid and fungal glucosamine was lowered in comparison with the other two treatments. No effect on the two amino sugars was observed after adding cellulose initially or subsequently during the second incubation period. This indicates that the differences in quality between sucrose and cellulose had a strong impact on the formation of microbial residues. However, the amino sugars did not indicate a preferential decomposition of microbial residues as N sources.     

Relationships between microbial indices in roots and silt loam soils forming a gradient in soil organic matter

Perennial rye grass (Lolium perenne) was grown in a greenhouse pot experiment on seven soils to answer the question whether the microbial colonisation of roots is related to existing differences in soil microbial indices. The soils were similar in texture, but differed considerably in soil organic matter, microbial biomass, and microbial community structure. Ergosterol and fungal glucosamine were significantly interrelated in the root material. This ergosterol was also significantly correlated with the average ergosterol content of bulk and rhizosphere soil. In addition, the sum of fungal C and bacterial C in the root material revealed a significant linear relationship with microbial biomass C in soil. The colonisation of roots with microorganisms increased apparently with an increase in soil microbial biomass. In the root material, microbial tissue consisted of 77% fungi and 23% bacteria. In soil, the fungal dominance was slightly, but significantly lower, with 70% fungi and 30% bacteria. Fungal glucosamine in the root material was significantly correlated with that in soil (r=0.65). This indicates a close relationship between the composition of dead microbial remains in soil and the living fraction in soil and root material for unknown reasons.     

Effects of addition of maize litter and earthworms on C mineralization and aggregate formation in single and mixed soils differing in soil organic carbon and clay content

C mineralization and aggregate stability directly depend upon organic matter and clay content, and both processes are influenced by the activity of microorganisms and soil fauna. However, quantitative data are scarce. To achieve a gradient in C and clay content, a topsoil was mixed with a subsoil. Single soils and the soil mixture were amended with 1.0 mg maize litter C g soil⁻¹ with and without endogeic earthworms (Aporrectodea caliginosa). The differently treated soils were incubated for 49 days at 15 °C and 40% water holding capacity. Cumulative C mineralization, microbial biomass, ergosterol content and aggregate fractions were investigated and litter derived C in bulk soil and aggregates were determined using isotope analyses. Results from the soil mixture were compared with the calculated mean values of the two single soils. Mixing of soil horizons differing in carbon and clay content stimulated C mineralization of added maize residues as well as of soil organic matter. Mixing also increased contents of macro-aggregate C and decreased contents of micro-aggregate C. Although A. caliginosa had a stimulating effect on C mineralization in all soils, decomposition of added litter by A. caliginosa was higher in the subsoil, whereas A. caliginosa decreased litter decomposition in the soil mixture and the topsoil. Litter derived C in macro-aggregates was higher with A. caliginosa than with litter only. In the C poor subsoil amended with litter, A. caliginosa stimulated the microbial community as indicated by the increase in microbial biomass. Furthermore, the decrease of ergosterol in the earthworm treated soils showed the influence of A. caliginosa on the microbial community, by reducing saprotrophic fungi. Overall, our data suggest both a decrease of saprotrophic fungi by selective grazing, burrowing and casting activity as well as a stimulation of the microbial community by A. caliginosa.     

Ergosterol and microbial biomass relationship in soil

Ergosterol and microbial biomass C were measured in 26 arable, 16 grassland and 30 forest soils. The ergosterol content ranged from 0.75 to 12.94 g g^-1 soil. The geometric mean ergosterol content of grassland and forest soils was around 5.5 g g^-1, that of the arable soils 2.14 g g^-1. The ergosterol was significantly correlated with biomass C in the entire group of soils, but not in the subgroups of grassland and forest soils. The geometric mean of the ergosterol: microbial biomass C ratio was 6.0 mg g^-1, increasing in the order grassland (5.1), arable land (5.4) and woodland (7.2). The ergosterol:microbial biomass C ratio had a strong negative relationship with the decreasing cation exchange capacity and soil pH, indicating that the fungal part of the total microbial biomass in soils increased when the buffer capacity decreased. The average ergosterol concentration calculated from literature data was 5.1 mg g^-1 fungal dry weight. Assuming that fungi contain 46% C, the conversion factor from micrograms ergosterol to micrograms fungal biomass C is 90. For soil samples, neither saponification of the extract nor the more effective direct saponification during extraction seems to be really necessary.     

Activity and degradation of streptomycin and cycloheximide in soil

Streptomycin and cycloheximide were added (3 and 2 mg g^-1 dry soil, respectively) single and in combination to a forest soil to follow their possible degradation and their effects on soil mineralization-immobilization processes. After 0, 1, 2, 4, 7, and 10 days of incubation at 25°C and 60% water-holding capacity, measurements were taken of microbial biomass C and N, the evolution of CO₂, exchangeable NH _inf4 ^sup+ , 0.5M K₂SO₄-extractable organic C, and total N in both unfumigated and CHCl₃-fumigated soil. The results indicated that during the first 2 days of incubation, soil microorganisms were killed by the antibiotics and/or by CHCl₃ and used subsequently as a substrate by the survivors. Thereafter, surviving microorganisms probably also started to use biocidal molecules as an energy and nutrient source. The ratios of biomass C to biomass N and of CO₂ evolved to net NH _inf4 ^sup+ produced indicated that both biocides had non-target effects for most of the incubation. Thus, streptomycin and cycloheximide are not suitable in determining the relative contribution from fungi and bacteria to mineralization-immobilization processes in soils.     

Improving soil structure by promoting fungal abundance with organic soil amendments

Building soil structure in agroecosystems is important because it governs soil functions such as air and water movement, soil C stabilization, nutrient availability, and root system development. This study examined, under laboratory conditions, effects of organic amendments comprised of differing proportions of labile and semi-labile C on microbial community structure and macroaggregate formation in three variously textured soils where native structure was destroyed. Three amendment treatments were imposed (in order of increasing C lability): vegetable compost, dairy manure, hairy vetch (Vicia villosa Roth). Formation of water stable macroaggregates and changes in microbial community structure were evaluated over 82 days. Regardless of soil type, formation of large macroaggregates (LMA, >2000 μm diameter) was highest in soils amended with vetch, followed by manure, non-amended control, and compost. Vetch and manure had greater microbially available C and caused an increase in fungal biomarkers in all soils. Regression analysis indicated that LMA formation was most strongly related to the relative abundance of the fungal fatty acid methyl ester (FAME) 18:2ω6c (r = 0.55, p < 0.001), fungal ergosterol (r = 0.58, p < 0.001), and microbial biomass (r = 0.57, p < 0.001). Non-metric multidimensional scaling (NMS) ordination of FAME profiles revealed that vetch and manure drove shifts toward fungal-dominated soil microbial communities and greater LMA formation in these soils. This study demonstrated that, due to their greater amounts of microbially available C, vetch or manure inputs can be used to promote fungal proliferation in order to maintain or improve soil structure.     

Microbial colonisation of roots as a function of plant species

Fifteen plants species were grown in the greenhouse on the same soil and sampled at flowering to obtain rhizosphere soil and root material. In both fractions, the data on fungal and bacterial tissue obtained by amino sugar analysis were compared with the total microbial biomass based on fumigation-extraction and ergosterol data. The available literature on glucosamine concentrations in fungi and on muramic acid concentrations in bacteria was reviewed to prove the possibility of generating conversion values for general use in root material. All microbial properties analysed revealed strong species-specific differences in microbial colonisation of plant roots. The root material contained considerable amounts of microbial biomass C and biomass N, reaching mean levels of 10.9 and 1.4 mg g⁻¹ dry weight, respectively. However, the majority of CHCl₃ labile C and N, i.e. 89 and 55% was root derived. The average amount of ergosterol was 13 μg g⁻¹ dry weight and varied between 0.0 for Phacelia roots and 45.5 μg g⁻¹ dry weight for Vicia roots. The ergosterol content in root material of mycorrhizal and non-mycorrhizal plant species did not differ significantly. Fungal glucosamine was converted to fungal C by multiplication by 9 giving a range of 7.1-25.9 mg g⁻¹ dry weight in the root material. Fungal C and ergosterol were significantly correlated. Bacterial C was calculated by multiplying muramic acid by 45 giving a range from 1.7 to 21.6 mg g⁻¹ dry weight in the root material. In the root material of the 15 plant species, the ratio of fungal C-to-bacterial C ranged from 1.0 in mycorrhizal Trifolium roots to 9.5 in non-mycorrhizal Lupinus roots and it was on average 3.1. These figures mean that the microbial tissue in the root material consists on average of 76% fungal C and 24% bacterial C. The differences in microbial colonisation of the roots were reflected by differences in microbial indices found in the rhizosphere soil, most strongly for microbial biomass C and ergosterol, but to some extent also for glucosamine and muramic acid.     

Does soil ergosterol concentration provide a reliable estimate of soil fungal biomass?

Our aim was to determine if soil ergosterol concentration provides a quantitative estimate of the soil fungal biomass concentration, as is usually assumed. This was done by comparing soil ergosterol measurements with soil fungal biomass (fungal biomass C) concentrations estimated by microscopic measurements and by the selective inhibition technique linked to substrate-induced respiration (SIR). The measurements were compared in a silty-clay loam soil given a range of previous treatments designed to increase or decrease the soil fungal biomass and so also to change the soil ergosterol concentration. The treatments used were ryegrass amendment, to increase the total and fungal biomass, and CHCl₃-fumigation and the addition of the biocides, captan, bronopol and dinoseb, to decrease both ergosterol and fungal biomass C concentrations. The mineralization of ergosterol following addition to sand innoculated with soil extract, and to a sandy loam soil, was also determined. The added ergosterol was little, if at all, degraded following addition to either sand or the unfumigated or fumigated soil during a 10 d aerobic incubation. Similarly, pesticide addition did not significantly change soil ergosterol concentrations yet the soil fungal biomass C concentration decreased significantly. Thus, the ratio: (soil ergosterol concentration/soil fungal biomass C concentration) was much higher in the pesticide-treated soils than the control soil. Following ryegrass amendment, soil ergosterol concentration increased from about 6-12 μg⁻¹ soil within 5 d and then decreased gradually to about 7 μg g⁻¹ soil by 20 d incubation. Changes in fungal biomass C (measured by direct microscopy) closely mirrored changes in soil ergosterol over this period. However, when the amended soil was fumigated and then incubated for a further 5 d, the initial ergosterol concentration declined from 7 to 5 μg g⁻¹ soil by 20 d incubation (a decline of about 0.4). The comparable decline in fungal biomass C was about eight-fold. Thus the ratio of ergosterol to fungal biomass C increased from 0.005 to about 0.01. There was a significant correlation (r>0.84, P<0.001) between soil ergosterol concentration and fungal biomass measured by either SIR or microscopy. However, three data points played a vital role in the correlation. When these points were excluded the relationship was very poor (r<0.4). Our results therefore suggest that substantial amounts of ergosterol may exist, other than in living cells, for considerable periods, with little, if any mineralization. Thus, these results indicate that ergosterol and fungal biomass C concentrations are not always closely correlated, due to the slow metabolism of ergosterol in recently dead fugal biomass and/or the existence of exocellular ergosterol in soil.     

Impact of carbon nanomaterials on microbial activity in soil

In this study, effects of an increase in concentration of fullerene-C_60, single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) or fullerene soot (FS) on overall microbial activity was investigated over a 21 d incubation period. Microbial utilisation of ¹⁴C-glucose and uptake of ¹⁴C-glucose into the microbial biomass was investigated. For CNM-amended soils, greater extents of ¹⁴C-glucose mineralisation were found in the C₆₀-amended soils compared to MWCNT-, SWCNT- or FS-amended soils. In addition, the 100 and 1000 mg kg⁻¹ were consistently found to have higher extents of mineralisation in C₆₀, MWCNT, SWCNT or FS-amended soils, respectively. Further, the incorporation of ¹⁴C-glucose into the microbial biomass declined slightly with an increase in concentration in the amended soils, but no consistent pattern was observed. As a result, the biophysical quotient (BQ) increased significantly (P < 0.05), as concentrations increased from 1 mg kg⁻¹ to 1000 mg kg⁻¹ in all C₆₀-, MWCNT-, SWCNT- and FS-amended soils. The results obtained from this study showed that the addition to carbon nanomaterials had no profound impacts on the overall microbial activity, and the overall influence of CNMs on soil microbial activity does not reveal a specific pattern in the short term.     

Immobilization and mineralization of nitrogen in a saline and alkaline soil during microbial use of sugarcane filter cake amended with glucose

A 42-day incubation was conducted to study the effect of glucose and ammonium addition adjusted to a C/N ratio of 12.5 on sugarcane filter cake decomposition and on the release of inorganic N from microbial residues formed initially. The CO₂ evolved increased in comparison with the non-amended control from 35% of the added C with pure +5 mg g⁻¹ soil filter cake amendment to 41% with +5 mg g⁻¹ soil filter cake +2.5 mg g⁻¹ soil glucose amendment to 48% with 5 mg g⁻¹ soil filter cake +5 mg g⁻¹ soil glucose amendment. The different amendments increased microbial biomass C and microbial biomass N within 6 h and such an increase persisted. The fungal cell-membrane component ergosterol initially showed a disproportionate increase in relation to microbial biomass C, which completely disappeared by the end of the incubation. The cellulase activity showed a 5-fold increase after filter cake addition, which was not further increased by the additional glucose amendment. The cellulase activity showed an exponential decline to values around 4% of the initial value in all treatments. The amount of inorganic N immobilized from day 0 to day 14 increased with increasing amount of C added, in contrast to the control treatment. After day 14, the immobilized N was re-mineralized at rates between 1.3 and 1.5 μg N g⁻¹ soil d⁻¹ in the treatments being more than twice as high as in the control treatment. This means that the re-mineralization rate is independent of the actual size of the microbial residues pool and also independent of the size of the soil microbial biomass.     

Influence of pH,dispersion methods,and different compounds on adenosine triphosphate recovery from soil

We studied the recovery of ATP from soil. A soil-water suspension was prepared by two different methods (simple stirring or ballottini mill treatment) at different pH levels and in the presence of different chemicals [Na₂SO₄, Na₃PO₄, Na₅P₃O₁₀, adenosine, ethylenediaminetetra-acetic acid (EDTA), TRIS]. The ATP recovery was evaluated by adding [³H]-8 ATP to the solution and comparing the values obtained by radioactivity measurements with those obtained by an enzymatic assay. Strongly acidic (pH lower than 1.0) or alkaline (pH 10.0) extractions yielded the best ATP recoveries compared with intermediate pH values. At pH 10.0, the addition of Na₃PO₄ or Na₅P₃O₁₀ gave a high level of ATP recovery, 68 and 96%, respectively. No ATP hydrolysis occurred under alkaline extraction conditions. Under acidic extraction conditions, the addition of adenosine, EDTA, Na₂SO₄, or Na₅P₃O₁₀ improved ATP recovery but it was never higher than 34%. The results were discussed in terms of the effects of different physical and chemical conditions on cell disruption, ATP stability, ATP interactions with soil components, and ATP solubilization.     

Usefulness of near-infrared spectroscopy to determine biological and chemical soil properties: Importance of sample pre-treatment

Near-infrared reflectance spectroscopy (NIRS) is known for its inexpensiveness, rapidity and accuracy and may become a useful tool for the assessment of soil quality. Objectives were (i) to evaluate the ability of NIRS to predict several chemical and biological properties of organically managed arable soils as well as the properties of grain yield from winter cereals for a closed population and (ii) to test whether the use of field-moist and pre-treated (quick-freezing followed by freeze-drying and grinding) samples will generate similar results. One hundred and sixteen soil samples from nine organically managed farms from Germany sampled in 2005 and 2006 were used for this investigation. Spectra of the near-infrared region (including the visible range, 400–2500 nm) from field-moist (<2 mm) or pre-treated soil samples were recorded. A modified partial least-square regression method and cross-validation were used to develop an equation over the whole spectrum (first–third derivation). For the pre-treated soils, good predictions were obtained for pH, contents of organic C, total N, plant-available P (Olsen) and exchangeable K (calcium-acetate-lactate (CAL)), contents of microbial biomass C and N (C_mic and N_mic) and ergosterol, basal respiration, metabolic quotient, the ratio of organic C/total N, the grain yield of winter cereals and grain nitrogen uptake. The RSC (the ratio of standard deviation of laboratory results to standard error of cross-validation) was greater than 2.0, the correlation coefficients (r) of a linear regression (measured against predicted values) were greater than or equal to 0.9 and the regression coefficients (a) ranged from 0.9 to 1.1. Similar good predictions were obtained if field-moist samples were used, with the exception of P (Olsen), K (CAL), metabolic quotient, grain yield of winter cereals and grain nitrogen uptake (satisfactory predictions) and ergosterol content (unsatisfactory prediction). Good predictions of the contents of Mg (CaCl₂) and microbial biomass P (P_mic) were achieved for field-moist but not for pre-treated samples. Despite sample preparation, only satisfactory predictions were obtained for the ratios of C_mic/N_mic and ergosterol/C_mic and grain nitrogen content (1.4RSC2.0, r0.8 and 0.8a1.2). However, unsatisfactory predictions for field-moist and pre-treated samples were achieved for the content of P (CAL), the nitrogen mineralisation rate and the ratios of C_mic/P_mic and basal respiration/nitrogen mineralisation rate. Our results demonstrate that biological soil properties can be predicted with NIRS for closed populations in both sample states. The pre-treatment should be used if samples have to be stored prior to infrared measurements for periods longer than a month.     

Vineyard soils under organic and conventional management—microbial biomass and activity indices and their relation to soil chemical properties

Eight vineyards in Pfaffenheim (P) and Turckheim (T) close to Colmar, France, forming four pairs of organic and conventional vineyards, were analyzed for microbial biomass and activity indices in relation to important soil chemical properties (carbon, nutrient elements, heavy metals) and also to differences between the bottom and top positions on the vineyard slope. The question was whether the vineyard management affects especially the soil microbiological indices. Three locations were on limestone (P-I, P-II, T-II), one on granite (T-I). The gravel content (>2 mm) ranged from 9 to 47%. The management systems had no significant main effect on the contents of organic C, total N, P, and S. The mean total contents of man-derived heavy metals decreased in the order Cu (164 μg g⁻¹ soil) > Zn (100 μg g⁻¹ soil) > Pb (32 μg g⁻¹ soil). The contents of microbial biomass C varied between 320 and 1,000 μg g⁻¹ soil. The significantly highest content was found at location P-II, the significantly lowest at the moderately acidic location T-I. The contents of microbial biomass N and adenosine triphosphate showed a similar trend. At location T-I, the fungal ergosterol-to-microbial biomass C ratio and the metabolic quotient qCO₂ were significantly highest, whereas the percentage of soil organic C present as microbial biomass C was lowest. Highest percentages of soil organic C present as microbial biomass C and lowest qCO₂ values were found in the organic in comparison with the conventional vineyards. None of the soil microbiological indices was significantly affected by the position on the slope, but all were significantly affected by the management system. This was mainly due to the highest index levels in the organic vineyard location P-II with the longest history in organic management.     

长期施肥处理对玉米生长期潮土微生物生物量和活度的影响

以1989年建立的中国科学院封丘农田生态系统国家试验站的长期定位试验为平台,研究经18a连续不同施肥处理后玉米季土壤微生物生物量碳氮和微生物活度的动态变化及其与土壤有机碳之间的相互关系,并探讨施肥措施对土壤微生物及其活性的影响。施肥处理包括:(1)有机肥(OM);(2)1/2化肥和1/2有机肥(1/2OM+1/2NPK);(3)氮磷钾肥(NPK);(4)氮磷肥(NP);(5)磷钾肥(PK);(6)氮钾肥(NK);(7)不施肥,即对照(CK)7个处理。结果表明,微生物生物量碳氮和微生物活度在玉米生长期内均有明显的时间变异性,其中微生物生物量碳与微生物活度的动态变化比较一致,其间的极显著相关关系表明潮土微生物生物量碳的变化可以在很大程度上代表土壤微生物活度的变化。施肥制度显著影响微生物生物量碳氮和微生物活度的变化,总体趋势为OM1/2OM+1/2NPKNPKNPPKNKCK,表明OM有利于保持土壤的生物化学环境及促进土壤的生物学活性;与OM处理相比,化学肥料的长期施用有降低土壤微生物生物量和微生物活度的趋势,尤其是缺素处理的表现更为明显,其中以缺磷处理的表现最为严重。土壤微生物生物量碳氮、微生物活度与土壤有机碳变化均呈极显著正相关。     

Prolonged simulated acid rain treatment in the subarctic: Effect on the soil respiration rate and microbial biomass

Humus chemistry and respiration rate, ATP, ergosterol, and muramic acid concentration as measures of chemical properties, microbial activity, biomass, and indicators of fungal and bacterial biomass were studied in a long-term acid rain experiment in the far north of Finnish Lapland. The treatments used in this study were dry control, irrigated control (spring water, pH 6), and two levels of simulated acid rain (pH 4 and pH 3). Originally (1985–1988), simulated acid rain was prepared by adding both H₂SO₄ and HNO₃ (1.9:1 by weight). In 1989 the treatments were modified as follows. In subarea 1 the treatments continued unchanged (H₂SO₄+HNO₃ in rain to pH 4 and pH 3), but in subarea 2 only H₂SO₄ was applied. The plots were sampled in 1992. The acid application affected humus chemistry by lowering the pH, cation exchange capacity, and base saturation (due to a decrease in Ca and Mg) in the treatment with H₂SO₄+HNO₃ to pH 4 (total proton load over 8 years 2.92 kmol ha^-1), whereas the microbial variables were not affected at this proton load, and only the respiration rate decreased by 20% in the strongest simulated acid rain treatment (total proton load 14.9 kmol ha^-1). The different ratios of H₂SO₄+HNO₃ in subareas 1 and 2 did not affect the results.     

Specific respiration rates, adenylates, and energy budgets of soil microorganisms after addition of transgenic Bt-maize straw

An arable soil was incubated with straw (stem+leaves) of two transgenic Bt-maize varieties (Novelis: event MON810 and Valmont: event Bt176) and the two corresponding near-isogenic varieties (Nobilis and Prelude). The aim was to evaluate the use of these substrates for microbial growth and maintenance in soil during early decomposition. The addition of Bt-maize straw increased CO₂ production rates and the specific respiration rates CO₂-C/microbial biomass C and CO₂-C/ATP significantly compared with the addition of non-Bt maize straw. This extra energy in the Bt-maize straw could not be used for microbial biomass or ATP and ADP production, and was lost for maintenance. In addition, increased death rates of microbial biomass occurred in the soils treated with the Bt-maize straw from day 3 to 21. Generally, most of the energy was stored in microbial biomass, whereas only 10% of energy was stored in ATP, and only 1-2% in ADP. The AEC (adenylate energy charge: (ATP+0.5×ADP)/(AMP+ADP+ATP)) was not affected by any treatment. The reasons for the lower efficiency of microbial substrate use after adding Bt-maize straw cannot be fully explained by the present experiment. However, a risk assessment has to look at the impact of transgenic plant material on soil microorganisms at different maturity stages.     

Determination of microbial biomass and fungal and bacterial distribution in cattle faeces

As an important component of organic fertilizers, animal faeces require methods for determining diet effects on their microbial quality to improve nutrient use efficiency in soil and to decrease gaseous greenhouse emissions to the environment. The objectives of the present study were (i) to apply the chloroform fumigation extraction (CFE) method for determining microbial biomass in cattle faeces, (ii) to determine the fungal cell-membrane component ergosterol, and (iii) to measure the cell-wall components fungal glucosamine and bacterial muramic acid as indices for the microbial community structure. Additionally, ergosterol and amino sugar data provide independent control values for the reliability of the microbial biomass range obtained by the CFE method. A variety of extractant solutions were tested for the CFE method to obtain stable extracts and reproducible microbial biomass C and N values, leading to the replacement of the original 0.5 M K₂SO₄ extractant for 0.05 M CuSO₄. The plausibility of the data was assessed in a 28-day incubation study at 25 °C with cattle faeces of one heifer, where microbial biomass C and N were repeatedly measured together with ergosterol. Here, the microbial biomass indices showed dynamic characteristics and possible shifts in the microbial community. In faeces of five different heifers, the mean microbial biomass C/N ratio was 5.6, the mean microbial biomass to organic C ratio was 2.2%, and the mean ergosterol to microbial biomass C ratio was 1.1‰. Ergosterol and amino sugar analysis revealed a significant contribution of fungi, with a percentage of more than 40% to the microbial community. All three methods are expected to be suitable tools for analysing the quality of cattle faeces.     

Fungal biomass development in a chronosequence of land abandonment

Based on biomass size, the contribution of fungi to nutrient cycling and soil properties is in general more important in natural ecosystems than in agro-ecosystems. Therefore, we expect an increase of fungal biomass after cessation of cultivation to values of a natural ecosystem. However, so far, information on fungal dynamics in ex-arable land is limited. We quantified fungal biomass in a chronosequence of 26 ex-arable fields in the Netherlands ranging from 1-34 years of abandonment. Agricultural lands and semi-natural heathlands were included as reference sites for initial and final stages of succession, respectively. Fungal biomass values were low at the start of land abandonment and increased during the first 2 years after abandonment. After this initial increase of fungal biomass no further increase was apparent, neither did we find any relations with time since abandonment and changes in soil acidity, organic matter content or organic matter quality (quantity of recalcitrant C and C:N ratio). Therefore, we conclude that the initial increase of fungal biomass is caused by stopping agricultural management activities. A phase of stabilization occurs for at least three decades in which the size of the fungal biomass did not change significantly. We observed much higher values for fungal biomass, total and recalcitrant carbon in the heathland sites. We propose that a change in abiotic soil properties is a prerequisite for further increase of fungal biomass towards levels of representative heathlands.