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1.
This study compares the functional capability of soils with differing microbial diversity. Soil microbial diversity was modified by either fumigation with reinoculation by unfumigated soil or fumigation with no reinoculation. Functional capability was assessed by following wheat straw decomposition in these soils and in an unfumigated control soil at three matric potentials (−5, −125 and −800 kPa). The changes in diversity after fumigation were compared with the effects of disturbance treatments (slow air-drying, rapid oven-drying, 2 mm sieving and 0.5 mm sieving) by studying patterns of in situ catabolic potential (ISCP) at 1 and 8 weeks. Five weeks after the fumigation treatments, the functional and phenotypic diversity of the soil microbial community, as revealed by patterns of ISCP and phospholipid fatty acid (PLFA) profiles, respectively, were greatly different from that in unfumigated soil. The effects of the fumigation reinoculation treatment on functional diversity were comparable with those caused by rapid oven-drying, but were greater than the effects of 0.5 mm sieving. These disturbance treatments caused persistent changes in functional diversity, whereas slow air-drying and 2 mm sieving had little influence on diversity. Rates of straw decomposition were initially greater in the fumigated reinoculated soil than in the unfumigated soil at all moisture potentials. In contrast, straw mineralisation rates in the fumigated uninoculated soil generally exceeded rates in unfumigated soil for a period after 14 d, which was shorter at greater moisture potentials. These rates resulted in total straw mineralisation in fumigated reinoculated soil exceeding that in unfumigated soil at all moisture potentials. Compared with the unfumigated soils, total straw mineralisation in fumigated uninoculated soil was less at −5 kPa, similar at −125 kPa and greater at −800 kPa. The results indicated that the decomposition function of soil with reduced functional diversity can be diminished under optimum moisture conditions, but is not invariably reduced when assessed under suboptimal moisture conditions. This indicated that decreases in the functional diversity of soil microbial communities may not consistently result in declines in soil functioning.  相似文献   

2.
The soils of the Antarctic dry valleys are exposed to extremely dry and cold conditions. Nevertheless, they contain small communities of micro-organisms that contribute to the biogeochemical transformations of the bioelements, albeit at slow rates. We have determined the dehydrogenase, β-glucosidase, acid and alkaline phosphatase and arylsulphatase activities and the rates of respiration (CO2 production) in laboratory assays of soils collected from a field experiment in an Antarctic dry valley. The objective of the field experiment was to test the responses of the soil microbial community to additions of C and N in simple (glucose and NH4Cl) and complex forms (glycine and lacustrine detritus from the adjacent lake comprising principally cyanobacterial necromass). The soil samples were taken 3 years after the experimental treatments had been applied. In unamended soil, all enzyme activities and respiration were detected indicating that the enzymatic capacity to mineralize organic C, P and S compounds existed in the soil, despite the very low organic matter content. Relative to the control (unamended soil), respiration was significantly increased by all the experimental additions of C and N except the smallest NH4Cl addition (1 mg N g−1 soil) and the smallest detritus addition (1.5 mg C g−1 soil and 0.13 mg N g−1 soil). The activities of all enzymes except dehydrogenase were increased by C and combined large C (10 mg C g−1 soil) and N additions, but either unchanged or diminished by addition of either N only or N (up to 10 mg N g−1 soil) with only small C (1 mg C g−1 soil) additions in the form of glucose and NH4Cl. This suggests that in the presence of a large amount of N, the C supply for enzyme biosynthesis was limited. When normalized with respect to soil respiration, only arylsulphatase per unit of respiration showed a significant increase with C and N additions as glucose and NH4Cl, consistent with S limitation when C and N limitations have been alleviated. Based on the positive responses of enzyme activity, detritus appeared to provide either conditions or resources which led to a larger biological response than a similar amount of C and more N added in the form of defined compounds (glucose, NH4Cl or glycine). Assessment of the soil microbial community by ester-linked fatty acid (ELFA) analysis provided no evidence of changes in the community structure as a result of the C and N supplementation treatments. Thus the respiration and enzyme activity responses to supplementation occurred in an apparently structurally stable or unresponsive microbial community.  相似文献   

3.
Particulate organic matter (POM) is more sensitive than total SOM to changes in management practices and, accordingly, may indicate changes in soil quality. A soil incubation study was conducted to determine the effects of added POM (75 to 250 μm size fraction), or macroorganic matter (MOM, 250 to 2000 μm size fraction) on C and N mineralization and microbial C and N content. A 1 kg composite made from 16 predominantly silt loam soils was amended with 10 g of POM, MOM or MOM ground to a reduced size of 75 to 250 μm (GMOM). The MOM amendment equaled 4.55-fold and POM equaled 1.60-fold of total MOM and POM found in the composite soil. Carbon mineralization of MOM and POM after 8 weeks was approximately 9 and 4%, respectively of the total MOM and POM-C added. Reducing the size of MOM to 75 to 250 μm did not affect mineralization. Nitrogen mineralization was slightly greater in the amended soils after 8 weeks and equaled 5 to 6% of the MOM or POM-total N added. Contribution of POM to total mineralized N from soil organic matter (SOM) in the composite soil was proportional to the POM content in SOM or approximately 12%. Amended soils had 25 to 42% more biomass-C than the control soil 2 weeks after amendment application. After 8 weeks, the amended soils contained about 32% more biomass-C. This increase in biomass-C at 8 weeks accounted for approximately 2% of the added C. At 8 weeks, microbial biomass-N in GMOM-, MOM- and POM-amended soils was about 56, 46 and 14% higher, respectively, than in the control soil. These increases were approximately 8% of the MOM-N added and 2% of the POM-N added. Increases in POM resulted in increases in soil respiration and microbial biomass-C and N, which also are suggested indicators of soil quality. Therefore, POM may be a suitable soil quality indicator that provides similar information as soil respiration or microbial biomass determinations.  相似文献   

4.
Soil microbes produce extracellular enzymes that mineralize organic matter and release carbon and nutrients in forms that can be assimilated. Economic theories of microbial metabolism predict that enzyme production should increase when simple nutrients are scarce and complex nutrients are abundant; however, resource limitation could also constrain enzyme production. We tested these hypotheses by monitoring enzyme activities and nutrient pools in soil incubations with added simple and complex nutrient compounds. Over 28 days of incubation, we found that an enzyme's activity increased when its target nutrient was present in complex but not simple form, and carbon and nitrogen were available. β-Glucosidase and acid phosphatase activities also increased in treatments where only carbon and nitrogen were added. Glycine aminopeptidase and acid phosphatase activities declined in response to ammonium and phosphate additions, respectively. In some cases, mineralization responses paralleled changes in enzyme activity—for example, β-glucosidase activity increased and respiration was 5-fold greater in soil incubations with added cellulose, ammonium, and phosphate. However, a doubling of acid phosphatase activity in response to collagen addition was not associated with any changes in phosphorus mineralization. Our results indicate that microbes produce enzymes according to ‘economic rules’, but a substantial pool of mineral stabilized or constitutive enzymes mediates this response. Enzyme allocation patterns reflect microbial nutrient demands and may allow microbes to acquire limiting nutrients from complex substrates available in the soil.  相似文献   

5.
We have much to learn about the roles of various groups of soil microorganisms in the decomposition of soil organic matter. Any changes in the type or amount of organic matter entering the soil, due to increasing atmospheric nitrogen (N) deposition and elevated carbon dioxide, could directly affect soil microbial community structure or the decompositional functions performed by the various microbial groups. We experimentally altered soil microbial communities using a factorial combination of trenching and in-growth bags crossed with fertilization treatments consisting of two forms of inorganic N and three N-containing organic molecules of increasing molecular weight and complexity. We tested three hypotheses: (1) Different components of soil microbial communities change in different ways following the application of fertilization treatments; (2) soil fungi decrease with increased inorganic N but increase following the application of organic molecules; and (3) activity of the extracellular enzymes peroxidase and phenol oxidase, which are important in lignin degradation, decrease following the addition of inorganic N. We found that the abundance of soil microbes and their composition (measured by lipid analysis) was significantly altered following the addition of glutamic acid, but not with inorganic N or more complex N-containing organic molecules. Lipids indicative of ectomycorrhizal fungi experienced the greatest increase in abundance. Extracellular enzyme activity, in contrast, changed very little and did not parallel changes in the structure of the soil microbial community that resulted from the isolation treatments. We conclude that small additions of N-containing organic compounds can cause changes in the structure of the soil microbial community but that community changes do not necessarily have an impact on extracellular enzyme activity.  相似文献   

6.
Microbial adaptation to salinity can be achieved through synthesis of organic osmolytes,which requires high amounts of energy;however,a single addition of plant residues can only temporarily improve energy supply to soil microbes.Therefore,a laboratory incubation experiment was conducted to evaluate the responses of soil microbes to increasing salinity with repeated additions of plant residues using a loamy sand soil with an electrical conductivity in saturated paste extract（ECe） of 0.6 dS m-1.The soil was kept non-saline or salinized by adding different amounts of NaCl to achieve ECe of 12.5,25.0 and 50.0 dS m-1.The non-saline soil and the saline soils were amended with finely ground pea residues at two rates equivalent to 3.9 and 7.8 g C kg-1 soil on days 0,15 and29.The soils receiving no residues were included as a control.Cumulative respiration per g C added over 2 weeks after each residue addition was always greater at 3.9 than 7.8 g C kg-1 soil and higher in the non-saline soil than in the saline soils.In the saline soils,the cumulative respiration per g C added was higher after the second and third additions than after the first addition except with3.9 g C kg-1 at ECe of 50 dS m1.Though with the same amount of C added(7.8 g C kg-1),salinity reduced soil respiration to a lesser extent when 3.9 g C kg-1 was added twice compared to a single addition of 7.8 g C kg-1.After the third residue addition,the microbial biomass C concentration was significantly lower in the soils with ECe of 25 and 50 dS m1 than in the non-saline soil at3.9 g C kg-1,but only in the soil with ECe of 50 dS m-1 at 7.8 g C kg-1.We concluded that repeated residue additions increased the adaptation of soil microbial community to salinity,which was likely due to high C availability providing microbes with the energy needed for synthesis of organic osmolytes.  相似文献   

7.
The impact of organic compounds present in different kinds of organic fertilizers, i.e., anaerobically digested household waste, composted organic household waste, swine manure, and cow manure, on microbial communities in arable soil was investigated using microcosms. Soil was amended with dried residues or organic extracts of the residues and incubated for 12 weeks at 25°C. The microbial community composition was investigated by phospholipid fatty acid (PLFA) analysis, and the community of ammonia-oxidizing bacteria (AOB) was assessed by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments, followed by sequencing. All dried residues increased the AOB activity, determined as potential ammonia oxidation, whereas the organic extracts from the thermophilically digested waste and the swine manure caused a decreased potential activity. However, no differences in the DGGE banding patterns were detected, and the same AOB sequences were present in all samples treated with the residue extracts. Moreover, the PLFA composition showed that none of the residue additions affected the overall microbial community structure in the soil. We conclude that the AOB community composition was not affected by the organic compounds in the fertilizers, although the activity in some cases was.  相似文献   

8.
Global warming in the Arctic may alter decomposition rates in Arctic soils and therefore nutrient availability. In addition, changes in the length of the growing season may increase plant productivity and the rate of labile C input below ground. We carried out an experiment in which inorganic nutrients (NH4NO3 and NaPO4) and organic substrates (glucose and glycine) were added to soils sampled from across the mountain birch forest-tundra heath ecotone in northern Sweden (organic and mineral soils from the forest, and organic soil only from the heath). Carbon dioxide production was then monitored continuously over the following 19 days. Neither inorganic N nor P additions substantially affected soil respiration rates when added separately. However, combined N and P additions stimulated microbial activity, with the response being greatest in the birch forest mineral soil (57% increase in CO2 production compared with 26% in the heath soil and 8% in the birch forest organic soil). Therefore, mineralisation rates in these soils may be stimulated if the overall nutrient availability to microbes increases in response to global change, but N deposition alone is unlikely to enhance decomposition. Adding either, or both, glucose and glycine increased microbial respiration. Isotopic separation indicated that the mineralisation of native soil organic matter (SOM) was stimulated by glucose addition in the heath soil and the forest mineral soil, but not in the forest organic soil. These positive ‘priming’ effects were lost following N addition in forest mineral soil, and following both N and P additions in the heath soil. In order to meet enhanced microbial nutrient demand, increased inputs of labile C from plants could stimulate the mineralisation of SOM, with the soil C stocks in the tundra-heath potentially most vulnerable.  相似文献   

9.
The conversion of secondary forests to larch plantations in Northeast China has resulted in a significant decline in soil available nitrogen (N) and phosphorus (P), and thus affects plant productivity and ecosystem functioning. Microbes play a key role in the recycling of soil nutrients; in turn, the availability of soil N and P can constrain microbial activity. However, there is little information on the relationships between available soil N and P and the microbial biomass and activity in larch plantation soil. We studied the responses of soil microbial respiration, microbial biomass and activity to N and P additions in a 120-day laboratory incubation experiment and assessed soil microbial properties in larch plantation soil by comparing them with the soil of an adjacent secondary forest. We found that the N-containing treatments (N and N + P) increased the concentrations of soil microbial biomass N and soluble organic N, whereas the same treatments did not affect microbial respiration and the activities of β-glucosidase, N-acetyl-β-glucosaminidase and acid phosphatase in the larch plantation. In addition, the concentration of microbial biomass P decreased with N addition in larch plantation soil. In contrast, N and N + P additions decreased microbial respiration, and N addition also decreased the activity of N-acetyl-β-glucosaminidase in the secondary forest soil. The P treatment did not affect microbial respiration in either larch plantation or secondary forest soils, while this treatment increased the activities of β-glucosidase and acid phosphatase in the secondary forest soil. These results suggested that microbial respiration was not limited by available P in either secondary forest or larch plantation soils, but microbial activity may have a greater P demand in secondary forest soil than in larch plantation soil. Overall, there was no evidence, at least in the present experiment, supporting the possibility that microbes suffered from N or P deficiency in larch plantation soil.  相似文献   

10.
Tannins are polyphenolic compounds that may influence litter decomposition, humus formation, nutrient (especially N) cycling and ultimately, plant nutrition and growth. The aim of this study was to determine the response of C and N transformations in soil to tannins of different molecular weight from Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.) needles, tannic acid and cellulose. Arginine was added to test whether the soil microbial community was limited by the amount of N, and arginine+tannin treatments were used to test whether the effects of tannins could be counteracted by adding N. Soil and needle samples were taken from adjacent 70-year-old Scots pine and Norway spruce stands located in Kivalo, northern Finland. Tannins were extracted from needles and fractioned based on molecular weight; the fractions were then characterized by LC-MS and GC-MS. Light fractions contained tannin monomers and dimers as well as many other compounds, whereas heavy fractions consisted predominantly of polymerized condensed tannins. Spruce needles contained more procyanidin than prodelphinidin units, while in pine needles prodelphinidin units seemed to be dominant. The fractions were added to soil samples, pine fractions to pine soil and spruce fractions to spruce soil, and incubated at 14 °C for 6 weeks. CO2 evolution was followed throughout the experiment, and the rates of net mineralization of N and net nitrification, concentration of dissolved organic N (DON) and amounts of microbial biomass C and N were measured at the end of the experiment. The main effects of the fractions were similar in both soils. Light fractions strongly enhanced respiration and decreased net N mineralization, indicating higher immobilization of N in the microbial biomass. On the contrary, heavy fractions reduced respiration and slightly increased net N mineralization, suggesting toxic or protein-precipitating effects. The effects of tannic acid and cellulose resembled those of light fractions. DON concentrations generally decreased during incubation and were lower with heavy fractions than with light fractions. No clear differences were detected between the effects of light and heavy fractions on microbial biomass C and N. Treatments that included addition of arginine generally showed trends similar to treatments without it, although some differences between light and heavy fractions became more obvious with arginine than without it. Overall, light fractions seemed to act as a labile source of C for microbes, while heavy fractions were inhibitors.  相似文献   

11.
Plant effects on ecosystem processes are mediated through plant-microbial interactions belowground and soil enzyme assays are commonly used to directly relate microbial activity to ecosystem processes. Live plants influence microbial biomass and activity via differences in rhizosphere processes and detrital inputs. I utilized six grass species of varying litter chemistry in a factorial greenhouse experiment to evaluate the relative effect of live plants and detrital inputs on substrate-induced respiration (SIR, a measure of active microbial biomass), basal respiration, dissolved organic carbon (DOC), and the activities of β-glucosidase, β-glucosaminidase, and acid phosphatase. To minimize confounding variables, I used organic-free potting media, held soil moisture constant, and fertilized weekly. SIR and enzyme activities were 2-15 times greater in litter-addition than plant-addition treatments. Combining live plants with litter did not stimulate microbial biomass or activity above that in litter-only treatments, and β-glucosidase activity was significantly lower. Species-specific differences in litter N (%) and plant biomass were related to differences in β-glucosaminidase and acid phosphatase activity, respectively, but had no apparent effect on β-glucosidase, SIR, or basal respiration. DOC was negatively related to litter C:N, and positively related to plant biomass. Species identity and living plants were not as important as litter additions in stimulating microbial activity, suggesting that plant effects on soil enzymatic activity were driven primarily by detrital inputs, although the strength of litter effects may be moderated by the effect of growing plants.  相似文献   

12.
Microbial activity has been highlighted as one of the main unknowns controlling the fate and turnover of soil organic matter (SOM) in response to climate change. How microbial community structure and function may (or may not) interact with increasing temperature to impact the fate and turnover of SOM, in particular when combined with changes in litter chemistry, is not well understood. The primary aim of this study was to determine if litter chemistry impacted the decomposition of soil and litter-derived carbon (C), and its interaction with temperature, and whether this response was controlled by microbial community structure and function. Fresh or pre-incubated eucalyptus leaf litter (13C enriched) was added to a woodland soil and incubated at 12, 22, or 32 °C. We tracked the movement of litter and soil-derived C into CO2, water-extractable organic carbon (WEOC), and microbial phospholipids (PLFA). The litter additions produced significant changes in every parameter measured, while temperature, interacting with litter chemistry, predominately affected soil C respiration (priming and temperature sensitivity), microbial community structure, and the metabolic quotient (a proxy for microbial carbon use efficiency [CUE]). The direction of priming varied with the litter additions (negative with fresh litter, positive with pre-incubated litter) and was related to differences in the composition of microbial communities degrading soil-C, particularly gram-positive and gram-negative bacteria, resulting from litter addition. Soil-C decomposition in both litter treatments was more temperature sensitive (higher Q10) than in the soil-only control, and soil-C priming became increasingly positive with temperature. However, microbes utilizing soil-C in the litter treatments had higher CUE, suggesting the longer-term stability of soil-C may be increased at higher temperature with litter addition. Our results show that in the same soil, the growth of distinct microbial communities can alter the turnover and fate of SOM and, in the context of global change, its response to temperature.  相似文献   

13.
The ratios of soil carbon (C) to nitrogen (N) and C to phosphorus (P) are much higher in Chinese temperate forest soils than in other forest soils, implying that N and P might limit microbial growth and activities. The objective of this study was to assess stoichiometric responses of microbial biomass, enzyme activities, and respiration to N and P additions. We conducted a nutrient (N, P, and N + P) addition experiment in two temperate soils under Korean pine (Pinus koraiensis) plantation and natural broadleaf forest in Northeast China and measured the microbial biomass C, N, P; the activities of β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), and acid and alkaline phosphomonoesterase (AP); and the microbial respiration in the two soils. Nitrogen addition increased microbial biomass N and decreased microbial biomass C-to-N ratio and microbial respiration in the two soils. Nitrogen addition decreased NAG activity to microbial biomass N ratio, P addition decreased AP activity to microbial biomass P ratio, and N, P, and N + P additions all increased BG activity to microbial biomass C ratio. These results suggest that microbial stoichiometry is not strictly homeostatic in response to nutrient additions, especially for N addition. The responses of enzyme activities to nutrient additions support the resource allocation theory. The N addition induced a decline in microbial respiration, implying that atmospheric N deposition may reduce microbial respiration, and consequently increase soil C sequestration in the temperate region.  相似文献   

14.
In many ecosystems, residues are added frequently to soil, in the form of root turnover and litter fall. However, in most studies on residue decomposition, residues are added once and there are few studies that have investigated the effect of frequent residue addition on C mineralization and N dynamics. To close this knowledge gap, we mixed mature wheat residue (C/N 122) into soil at a total rate of 2% w/w once at the start (R1×), every 16 days (R4×), every 8 days (R8×) or every 4 days (R16×). Un-amended soil served as control. All treatments were mixed every 4 days. Soil respiration was measured continuously over the 80-day incubation. Inorganic N, K2SO4-extractable C and N, chloroform-labile C and N (as an estimate of microbial biomass C and N), soil pH and microbial community composition were assessed every 16 days. Increasing frequency of residue addition increased C mineralization per g residue. Compared to R1×, cumulative respiration per g residue at the end of the incubation (day 80) was increased by 57, 82 and 92% in R4×, R8× and R16×, respectively. The largest differences in soil respiration per g residue occurred in the first 30 days. Despite large increases in cumulative respiration, frequent residue addition did not affect inorganic N or K2SO4-extractable N concentrations, chloroform-labile C and N or soil pH. Compared to the control, all residue treatments resulted in increases in chloroform-labile C and N and soil pH but decreased inorganic and K2SO4-extractable N. Microbial community composition was affected by residue addition, however there were no consistent differences among residue treatments. It is concluded that experiments with single residue additions may underestimate residue decomposition rates in the field. The increased C mineralization caused by frequent residue additions does not appear to be due to an increased microbial biomass or changes in microbial community composition, but rather to increased C mineralization per unit biomass.  相似文献   

15.
 Using soils from field plots in four different arable crop experiments that have received combinations of manure, lime and inorganic N, P and K for up to 20 years, the effects of these fertilizers on soil chemical properties and estimates of soil microbial community size and activity were studied. The soil pH was increased or unaffected by the addition of organic manure plus inorganic fertilizers applied in conjunction with lime, but decreased in the absence of liming. The soil C and N contents were greater for all fertilized treatments compared to the control, yet in all cases the soil samples from fertilized plots had smaller C:N ratios than soil from the unfertilized plots. The soil concentrations of all the other inorganic nutrients measured were greater following fertilizer applications compared with the unfertilized plots, and this effect was most marked for P and K in soils from plots that had received the largest amounts of these nutrients as fertilizers. Both biomass C determined by chloroform fumigation and glucose-induced respiration tended to increase as a result of manure and inorganic fertilizer applications, although soils which received the largest additions of inorganic fertilizers in the absence of lime contained less biomass C than those to which lime had been added. Dehydrogenase activity was lower in soils that had received the largest amounts of fertilizers, and was further decreased in the absence of lime. This suggests that dehydrogenase activity was highly sensitive to the inhibitory effects associated with large fertilizer additions. Potential denitrification and anaerobic respiration determined in one soil were increased by fertilizer application but, as with both the microbial biomass and dehydrogenase activity, there were significant reductions in both N2O and CO2 production in soils which received the largest additions of inorganic fertilizers in the absence of lime. In contrast, the size of the denitrifying component of the soil microbial community, as indicated by denitrifying enzyme activity, was unaffected by the absence of lime at the largest rate of inorganic fertilizer applications. The results indicated differences in the composition or function of microbial communities in the soils in response to long-term organic and inorganic fertilization, especially when the soils were not limited. Received: 10 March 1998  相似文献   

16.
Biogeochemical mechanisms at microscale regions within soil macroaggregates strengthen aggregates during repeated DW cycles. Knowledge of additional biogeochemical processes that promote the movement of dissolved organic carbon (DOC) into and throughout soil aggregates and soil aggregate stabilization are essential before we can more accurately predict maximum carbon (C) sequestration by soils subjected to best management practices. We investigated the spatial distribution of 13C-glucose supplied to individual soil macroaggregate surfaces and subjected to multiple drying and wetting (DW) cycles. Subsequent distribution of added glucose-C, CO2 respiration, increased microbial community activity and concomitant changes in soil aggregate stabilization were monitored. Moist macroaggregates were treated with no DW cycles and zero glucose C (Control), 5 DW cycles and zero glucose (DW0G), and 5 DW cycles with additions of 250 μg glucose-13C/g soil during each cycle (DW+G). Repeated additions of glucose-C to aggregate surfaces reduced the mineralization of pre-existing soil C by an average of 45% and established concentric gradients of glucose-derived C. It is concluded these increasing gradients promoted the diffusion of soluble C into interior regions and became less available to microbial respiration. Spatial gradients of glucose-derived C within aggregates influenced a shift in the abundance of unique ribotypes spatially distributed within aggregates. Rapid decreases in the mineralization rates of glucose-C during repeated DW cycles suggested greater C sequestration by either physical restriction of microbes or chemical sorption of new C that diffused into aggregates. Aggregate stability decreased significantly following 2-3 DW cycles, when glucose-C was not added. Additions of glucose-C with each DW cycle maintained soil aggregate stability equal to the moist but not cycled control throughout the 5 DW cycles of this study. These data simulate the strengthening of soil aggregates in no tillage agroecosystems which provides continuous additions of DOC compounds generated by decomposing plant residues on the soil surface, and root exudates and decomposition, as well as the mineralization of POM materials within nondisturbed soil profiles.  相似文献   

17.
Plant inputs of organic material to soil are thought to be key determinants of microbial activity, community composition and processes. However, the identity of organisms utilising these chemically diverse inputs is not well understood. In this study, we applied tracer amounts of highly enriched, 13C-labelled plant tissue fractions (whole, insoluble and soluble) to soil cores that either allowed or prevented access to roots and mycorrhizal fungi. For all tissue fractions, C derived from the additions was detected rapidly (<2 h after additions) in soil respiration. The additions did not alter microbial community structure, but their fate was strongly dependent on the addition type. The mineralisation of the soluble fraction was the most rapid and was recovered predominantly in bacterial PLFA biomarkers. In contrast, the insoluble addition was mineralised more slowly and recovered in fungal biomarkers to a greater extent. The presence of roots and/or mycorrhizas did not significantly affect rates of mineralisation or the biological fate of additions. A second harvest indicated that the distribution of substrate-derived C within the microbial community was still distinct (i.e. dependent on the form of addition) after 49 d, but with accumulation of 13C within the enchytraeid biomass. The results indicate that under the conditions of this experiment, transfer of C between microbial groups is relatively slow, suggesting that the range of chemical forms of plant inputs are likely important in maintaining microbial community structure in soils.  相似文献   

18.
Altered rates of native soil organic matter (SOM) mineralisation in the presence of labile C substrate (‘priming’), is increasingly recognised as central to the coupling of plant and soil-biological productivity and potentially as a key process mediating the C-balance of soils. However, the mechanisms and controls of SOM-priming are not well understood. In this study we manipulated microbial biomass size and composition (chloroform fumigation) and mineral nutrient availability to investigate controls of SOM-priming. Effects of applied substrate (13C-glucose) on mineralisation of native SOM were quantified by isotopic partitioning of soil respiration. In addition, the respective contributions of SOM-C and substrate-derived C to microbial biomass carbon (MBC) were quantified to account for pool-substitution effects (‘apparent priming’). Phospholipid fatty acid (PLFA) profiles of the soils were determined to establish treatment effects on microbial community structure, while the 13C-enrichment of PLFA biomarkers was used to establish pathways of substrate-derived C-flux through the microbial communities. The results indicated that glucose additions increased SOM-mineralisation in all treatments (positive priming). The magnitude of priming was reduced in fumigated soils, concurrent with reduced substrate-derived C-flux through putative SOM-mineralising organisms (fungi and actinomycetes). Nutrient additions reduced the magnitude of positive priming in non-fumigated soils, but did not affect the distribution of substrate-derived C in microbial communities. The results support the view that microbial community composition is a determinant of SOM-mineralisation, with evidence that utilisation of labile substrate by fungal and actinomycete (but not Gram-negative) populations promotes positive SOM-priming.  相似文献   

19.
The objectives of this work were to (a) investigate the short-term effects of applications of mineral fertilizer, municipal solid waste (MSW) compost, and two sewage sludges (SSs) subjected to different treatments (composting and thermal drying) on microbial biomass and activity of soil by measuring microbial biomass C, adenosine 5′-triphosphate content, basal respiration, and dehydrogenase, catalase, urease, phosphatase, β-glucosidase, and N-α-benzoyl-l-argininamide-hydrolyzing activities and (b) explore the relationships between soil microbiological, biochemical, and chemical properties and wheat yields under semiarid field conditions by principal component analysis. The additions of MSW compost, SS compost, and thermally dried SS did not affect significantly soil microbial biomass, as compared to mineral fertilization and no amendment. However, microbial activity increased in organically amended soils, probably due to the stimulating effect of the added decomposing organic matter. Changes in soil microbiological and biochemical properties showed no significant relationships with wheat yields, probably because plant growth was primarily water-limited, as typically occurs in semiarid regions.  相似文献   

20.
Nitrogen (N) deposition to semiarid ecosystems is increasing globally, yet few studies have investigated the ecological consequences of N enrichment in these ecosystems. Furthermore, soil CO2 flux – including plant root and microbial respiration – is a key feedback to ecosystem carbon (C) cycling that links ecosystem processes to climate, yet few studies have investigated the effects of N enrichment on belowground processes in water-limited ecosystems. In this study, we conducted two-level N addition experiments to investigate the effects of N enrichment on microbial and root respiration in a grassland ecosystem on the Loess Plateau in northwestern China. Two years of high N additions (9.2 g N m−2 y−1) significantly increased soil CO2 flux, including both microbial and root respiration, particularly during the warm growing season. Low N additions (2.3 g N m−2 y−1) increased microbial respiration during the growing season only, but had no significant effects on root respiration. The annual temperature coefficients (Q10) of soil respiration and microbial respiration ranged from 1.86 to 3.00 and 1.86 to 2.72 respectively, and there was a significant decrease in Q10 between the control and the N treatments during the non-growing season but no difference was found during the growing season. Following nitrogen additions, elevated rates of root respiration were significantly and positively related to root N concentrations and biomass, while elevated rates of microbial respiration were related to soil microbial biomass C (SMBC). The microbial respiration tended to respond more sensitively to N addition, while the root respiration did not have similar response. The different mechanisms of N addition impacts on soil respiration and its components and their sensitivity to temperature identified in this study may facilitate the simulation and prediction of C cycling and storage in semiarid grasslands under future scenarios of global change.  相似文献   

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