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1.
Alkaline and acid phosphomonoesterase, β-glucosidase, arylsulfatase, protease and urease activities, CO 2-C evolution and ATP content were monitored in long-term Cd-contaminated (0-40 mg Cd kg −1 dry weight soil) sandy soils, kept under maize or ‘set aside’ regimes, amended with plant residues. The organic matter input increased soil respiration, ATP contents and hydrolase activities in all soils. However, the Cd-contaminated soils had significantly higher metabolic quotients ( qCO 2), as calculated by the CO 2-to-ATP ratio, and significantly lower hydrolase activities and hydrolase activity-to-ATP ratios for alkaline phosphomonoesterase, arylsulfatase and protease activities, compared with the respective uncontaminated soils. The ratios between acid phosphomonoesterase, β-glucosidase and urease activities and ATP were unaffected. A significantly higher qCO 2/ μ ratio, an expression of maintenance energy, was observed in most of the contaminated soils, indicating that more energy was required for microbial synthesis in the presence of high Cd concentrations. It was concluded that exposure to high Cd concentrations led to a less efficient metabolism, which was responsible for lower enzyme activity and synthesis and lower hydrolase activity-to-ATP ratios observed in these Cd-contaminated soils. 相似文献
2.
Soil pH and calcium carbonate contents are often hypothesized to be important factors controlling organic matter turnover in agricultural soils. The aim of this study was to differentiate the effects of soil pH from those related to carbonate equilibrium on C and N dynamics. The relative contributions of organic and inorganic carbon in the CO 2 produced during laboratory incubations were assessed. Five agricultural soils were compared: calcareous (74% CaCO 3), loess (0.2% CaCO 3) and an acidic soil which had received different rates of lime 20 years ago (0, 18 or 50 t ha −1). Soil aggregates were incubated with or without rape residues under aerobic conditions for 91 days at 15 °C. The C and N mineralized, soil pH, O 2 consumption and respiratory quotient (RQ=ΔCO 2/ΔO 2) were monitored, as well as the δ 13C composition of the evolved CO 2 to determine its origin (mineral or organic). Results showed that in non-amended soils, the cumulative CO 2 produced was significantly greater in the limed soil with a pH>7 than in the same soil with less or no lime added, whereas there was no difference in N mineralization or in O 2 consumption kinetics. We found an exponential relationship between RQ values and soil pH, suggesting an excess production of CO 2 in alkaline soils. This CO 2 excess was not related to changes in substrate utilization by the microbial biomass but rather to carbonates equilibrium. The δ 13C signatures confirmed that the CO 2 produced in soils with pH>7 originated from both organic and mineral sources. The contribution of soil carbonates to CO 2 production led to an overestimation of organic C mineralization (up to 35%), the extent of which depended on the nature of soil carbonates but not on the amount. The actual C mineralization (derived from organic C) was similar in limed and unlimed soil. The amount of C mineralized in the residue-amended soils was ten times greater than in the basal soil, thus masking the soil carbonate contribution. Residue decomposition resulted in a significant increase in soil pH in all soils. This increase is attributed to the alkalinity and/or decarboxylation of organic anions in the plant residue and/or to the immobilization of nitrate by the microbial biomass and the corresponding release of hydroxyl ions. A theoretical composition (C, O, H, N) of residue and soil organic matter is proposed to explain the RQ measured. It emphasizes the need to take microbial biomass metabolism, O 2 consumption due to nitrification and carbon assimilation yield into account when interpreting RQ data. 相似文献
3.
We examined the long-term effects of cattle slurry, applied at high rates, on microbial biomass, respiration, the microbial quotient ( qCO 2) and various soil enzyme activities. In March, June, July, and October 1991, slurry-amended grassland soils (0–10 cm) contained significantly higher levels of microbial biomass, N mineralization and enzyme activities involved in N, P, and C cycling. With microbial biomass as the relative value, the results revealed that the slurry treatment influenced enzyme production by the microbial biomass. High levels of urease activity were the result not only of a larger microbial biomass, but also of higher levels of enzmye production by this microbial biomass. The ratio of alkaline phosphatase and xylanase to microbial biomass was nearly constant in the different treatments. The metabolic quotient ( qCO 2) declined with increased levels of slurry application. Therefore it appears that microorganisms in slurry-amended soils require less C and energy if there is no competition for nutrients. The results of this study suggest that urease activity, nitrification, and respiration (metabolic quotient) can be used as indicators of environmental stress, produced by heavy applications of cattle slurry. 相似文献
4.
Wetlands have been recognized as a soil carbon (C) sink due to low decomposition. As decomposition is largely controlled by the availability of soil nitrogen (N), an elevated anthropogenic N input could influence the C balance in wetlands. However, the effects of the form of N on decomposition are poorly understood. Here, a 54-day laboratory incubation experiment was conducted, with a diel cycle (day: 22 °C for 13 h; night: 17 °C for 11 h) in order to determine how the dominant N form influences the mineralization of soil C in two adjacent wetland soils, with distinct physicochemical characteristics. Three combinations of N compounds were added at three different rates (0, 30, 60 kg N ha −1 yr −1): Ammonium dominant (NH 4Cl + NH 4NO 3); nitrate dominant (NH 4NO 3 + NaNO 3); and ammonium nitrate treatments (NH 4NO 3). In the acidic soil, the CO 2 efflux was reduced with N additions, especially with NH 4NO 3 treatment. In addition, decreases in the microbial enzyme activities ( β-glucosidase, N-acetyl-glucosaminidase, phosphatase, and phenol oxidase) and soil pH were observed with NH 4NO 3 and -dominant treatment. Under alkaline conditions, marginal changes in response to N additions were observed in the soil CO 2 efflux, extractable DOC, simple substrate utilization, enzyme activities and pH. A regression analysis revealed that the changes in pH and enzyme activities after fertilization significantly influenced the soil CO 2 efflux. Our findings suggest that the form of N additions could influence the rate of C cycling in wetland soils via biological (enzyme activities) and chemical (pH) changes. 相似文献
5.
The short-term pulse of carbon (C) and nitrogen (N) mineralization that accompanies the wetting of dry soils may dominate annual C and N production in many arid and semi-arid environments characterized by seasonal transitions. We used a laboratory incubation to evaluate the impact of short-term fluctuations in soil moisture on long-term carbon and nitrogen dynamics, and the degree to which rewetting enhances C and N release. Following repeated drying and rewetting of chaparral soils, cumulative CO 2 release in rewet soils was 2.2-3.7 times greater than from soils maintained at equivalent mean soil moisture and represented 12-18% of the total soil C pool. Rewetting frequency did not affect cumulative CO 2 release but did enhance N turnover, and net N mineralization and nitrification increased with rewetting in spite of significant reductions in nitrification potential. Litter addition decreased inorganic N release but enhanced dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) from dry soils, indicating the potential importance of a litter-derived pulse to short-term nutrient dynamics. 相似文献
6.
ABSTRACT Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at ?8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH 4 uptake and from 70 to 90% WFPS for N 2O and CO 2 emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N 2O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g ?1 C. Cumulative soil CO 2 emissions and CH 4 uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N 2O, CO 2, and CH 4 fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties. 相似文献
7.
Several studies show that increases in soil temperature result in higher N mineralization rates in soils. It is, however, unclear if additional N is taken up by the vegetation or accumulates in the soil. To address this question two small, forested catchments in southern Norway were experimentally manipulated by increasing air temperature (+3°C in summer to +5°C in winter) and CO 2 concentrations (+200 ppmv) in one catchment (CO 2T-T) and soil temperature (+3°C in summer to +5°C in winter) using heating cables in a second catchment (T-T). During the first treatment year, the climate treatments caused significant increases in soil extractable NH 4 under Vaccinium in CO 2T-T. In the second treatment year extractable NH 4 in CO 2T-T and NO 3 in T-T significantly increased. Soil solution NH 4 concentrations did not follow patterns in extractable NH 4 but changes in soil NO 3 pools were reflected by changes in dissolved NO 3. The anomalous behavior of soil solution NH 4 compared to NO 3 was most likely due to the higher NH 4 adsorption capacity of the soil. The data from this study showed that after 2 years of treatment soil inorganic N pools increased indicating that increases in mineralization, as observed in previous studies, exceeded plant demand and leaching losses. 相似文献
8.
Differences in soil structure created by tillage systems are often believed to have large impacts on C and N mineralization, in turn influencing total soil C and N stocks, CO 2 emissions and soil mineral N supply. The objectives of our work were therefore (i) to study C and N mineralization in undisrupted fresh soils from long-term conventional till (CT) and no-till (NT) systems in northern France and (ii) to evaluate at which scale soil structure plays a significant role in protecting organic matter against C and N mineralization. The in situ heterogeneity of soil structure was taken into account during sampling. Two megastructure zones induced by tillage and compaction were identified in the ploughed layer of CT: zones with loose structure (CT Loose) and clods with dense structure (CT Dense). The soil samples in NT were taken from layers that differed in both structure and organic matter content (NT 0-5 and NT 5-20). Soil from the two zones of different megastructure in CT showed similar levels of protection and similar C and N mineralization. Undisrupted soil from NT 0-5 showed greater absolute and specific C and N mineralization than CT Loose, CT Dense and NT 5-20. Limited soil structure destruction (sieving through 2 mm) had no effect on C and N mineralization. Increased disturbance (sieving down to 250 μm) only induced a significant increase of both C and N mineralization in the 5-20 cm layer of NT. Further disruption of soil structures (sieving through 50 μm) resulted in greater C and N mineralization for all treatments except C mineralization in the upper layer of NT. Protection in the four structural zones in CT and NT was, in general, greatest in the NT deeper layer and least in the NT upper layer. Our results therefore suggest that physical protection in the 5-20 cm soil layer can partly account for larger C and N stocks in NT, but that the large C and N concentrations in the 0-5 cm soil layer are determined by mechanisms other than physical OM protection. 相似文献
9.
The ATP content, soil respiration, bacterial community composition, and gross N mineralization and immobilization rates were monitored under laboratory condition at 25 °C for 28 d in a model system where low molecular weight root exudates (glucose and oxalic acid) were released by a filter placed on the surface of a forest soil also treated with 15N, so as to simulate rhizosphere conditions. Periodically, the soil was sampled from two layers, 0-2 and 6-14 mm below the filter's surface, which were indicated as rhizosphere and bulk soils, respectively. The isotope dilution technique was used to determine the effect of these low molecular weight organic compounds (LMWOCs) on gross N mineralization and immobilization rates. From 0 to 3 d both glucose and oxalic acid amended soils showed a rapid evolution of CO 2, more pronunced in the latter treatment together with a decrease in the amount of mineral N of the rhizosphere soil, probably due to N immobilization. Nevertheless, these changes were accompanied by a very small increase in the net ATP content probably because the low C application rate stimulated microbial activity but microbial growth only slightly. A positive ‘priming effect’ probably developed in the oxalic acid amended soil but not in the glucose amended soil. Gross N mineralization and immobilization rates were only observed in the rhizosphere soil, probably due to the greater C and N concentrations and microbial activity, and were a little higher in both amended soils than in the control soil, only between 1 and 7 d. Both glucose and oxalic acid influenced the bacterial communities of the rhizosphere soil, as new bands in the DGGE profiles appeared at 3 and 7 d. Glucose induced lower changes in the bacterial community than oxalic acid, presumably because the former stimulated a larger proportion of soil microorganisms whereas the latter was decomposed by specialized microorganisms. Peaks of net daily soil respiration and net ATP content and the appearence of new dominant bacterial populations were shifted in time, probably because there was less ATP synthesis and DGGE patterns changed after complete substrate mineralization. 相似文献
10.
PurposeImproving knowledge of how soil organic carbon (SOC) mineralization responds to excreta application is essential to better understand whether wetland carbon (C) pools will react to grazing. We investigated microbial activity and community structure in the different treatments of excreta addition experiments to examine how soil C mineralization responds to the excreta input in terms of microbial activities and compositions in wetland soils. Materials and methodsThe microcosms of mineralization incubation of excreta addition were established. The structure of the microbial community was described by the fatty acid composition of the phospholipids (PLFA). The methylumbelliferyl-linked substrates (MUB) and l-dihydroxyphenylalanine (L-DOPA) substrates were used to investigate the activities of β-glucosidase (BG), N-acetyl-glucosaminidase (NAG), acid phosphatase (AP), cellobiohydrolase (CBH), and phenol oxidase (PO). Results and discussionExcreta addition altered the cumulative C mineralization in swamp meadow (SM) and peatland (PL) soils, but SM was lower than PL. Excreta addition increased the biomass of individual PLFA and the fungi/bacteria ratio, suggesting that microbes are stimulated by nutrients and that the soil microbial community composition is modified by excreta inputs. The hydrolytic enzyme activities were higher in the PL soils than in the SM soils, but the trend was opposite for PO activity. The changes in pH, fungi, actinomycetes (ACT), AP, and CBH after yak fecal input significantly influenced the soil CO2 efflux. Our findings suggest that yak grazing could influence the rate of C cycling in wetland soils by influencing microbial communities, enzyme activities, and soil pH. ConclusionsThis study suggest that the yak excreta addition increased cumulative C mineralization in SM and PL soils, and the effect of dung addition was more significant than urine addition. The effect of yak excreta addition on SOC mineralization was related with the soil pH, microorganism structure, and enzyme activity which modified by the excreta addition. Soil pH, fungi, AP, and CBH were positively correlated with SOC mineralization, but ACT was negatively correlated with SOC mineralization. In addition, the changes in C and N sources with yak excreta addition play an important role in altering microbial enzyme activities. The input of yak feces into wetlands because of grazing could increase SOC mineralization and thereby promote C emission. 相似文献
11.
The aim of this work was to calculate indices of hydrolase production (Pr) and persistence (Pe) through simple arithmetical
calculations. Changes in acid and alkaline phosphomonoesterase, phosphodiesterase, urease, protease, and β-glucosidase activities
were monitored under controlled conditions in seven soils with a wide range of properties, in which microbial growth was stimulated
by adding glucose and nitrogen. Glucose mineralization was monitored by CO 2–C evolution, and microbial growth was quantified by determining the soil adenosine triphosphate (ATP) content. Hydrolase
Pr and Pe indices were numerically quantified by the following relationships: Pr = H / t
H
and Pe = ( r / H)Δ t, respectively, where H indicates the peak value of each measured hydrolase activity, t
H
is the time of the peak value, r indicates the residual activity value, and Δ t is the time interval t
r − t
H, where t
r is the time of the residual activity value. Addition of glucose and N-stimulated soil respiration increased ATP content and
stimulated the production of the measured hydrolase activities in all soils; the measured variable reached a maximum value
and then decreased, returning to the value of the control soil. Apart from β-glucosidase activity, whose activity was not
stimulated by glucose and N addition, the other measured hydrolase activities showed a trend that allowed us to calculate
the Pr and Pe indices using the above-mentioned equations. Acid phosphomonoesterase and protease Pr values were significantly
higher in soils under forest or set aside management; the alkaline phosphomonoesterase and phosphodiesterase Pr values were
generally higher in the neutral and alkaline soils, and the urease Pr values showed no obvious relationships with soil pH
or management. Concerning the persistence of enzyme activities, Pe values of the acid phosphomonoesterase activity were significantly
higher in the acidic soils, and those of urease activity were higher in acidic soils and the Bordeaux neutral soil. No relationships
were observed between Pe values of alkaline phosphomonoesterase, phosphodiesterase, or protease activities and soil pH or
management. The different responses of hydrolases were discussed in relation to soil properties, microbial growth, and regulation
at the enzyme molecular level. 相似文献
12.
Copper-based fungicides have been applied in apple orchards for a long time, which has resulted in increasing soil Cu concentration. However, the microbial and enzyme properties of the orchard soils remain poorly understood. This study aimed to evaluate the effect of long-term application of Cu-based fungicides on soil microbial (microbial biomass carbon (C mic), C mineralization, and specific respiration rate) and enzyme (urease, acid phosphatase, and invertase activities) properties in apple orchards. Soil samples studied were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil as for reference. The mean Cu concentrations of orchard soils significantly increased with increasing orchard ages ranging from 21.8 to 141 mg kg −1, and the CaCl 2-extractable soil Cu concentrations varied from 0.00 to 4.26 mg kg −1. The soil mean C mic values varied from 43.6 to 116 mg kg −1 in the orchard soils, and were lower than the value of the reference soil (144 mg kg −1). The ratio of soil C mic to total organic C (C org) increased from 8.10 to 18.3 mg C mic g −1 C org with decreasing orchard ages, and was 26.1 mg C mic g −1 C org for the reference soil. A significant correlation was observed between total- or CaCl 2-extractable soil Cu and soil C mic or C mic/C org, suggesting that the soil Cu was responsible for the significant reductions in C mic and C mic/C org. The three enzyme activity assays also showed the similar phenomena, and declined with the increasing orchard ages. The mean soil C mineralization rates were elevated from 110 to 150 mg CO 2-C kg −1 soil d −1 compared with the reference soil (80 mg CO 2-C kg −1 soil d −1), and the mean specific respiration rate of the reference soil (0.63 mg CO 2-C mg −1 biomass C d −1) was significantly smaller than the orchard soils from 1.19 to 3.55 mg CO 2-C mg −1 biomass C d −1. The soil C mineralization rate and the specific respiration rate can be well explained by the CaCl 2-extractable soil Cu. Thus, the long-term application of copper-based fungicides has shown adverse effects on soil microbial and enzyme properties. 相似文献
13.
Pyrogenic carbon (biochar) amendment is increasingly discussed as a method to increase soil fertility while sequestering atmospheric carbon (C). However, both increased and decreased C mineralization has been observed following biochar additions to soils. In an effort to better understand the interaction of pyrogenic C and soil organic matter (OM), a range of Florida soils were incubated with a range of laboratory-produced biochars and CO 2 evolution was measured over more than one year. More C was released from biochar-amended than from non-amended soils and cumulative mineralized C generally increased with decreasing biomass combustion temperature and from hardwood to grass biochars, similar to the pattern of biochar lability previously determined from separate incubations of biochar alone.The interactive effects of biochar addition to soil on CO 2 evolution (priming) were evaluated by comparing the additive CO 2 release expected from separate incubations of soil and biochar with that actually measured from corresponding biochar and soil mixtures. Priming direction (positive or negative for C mineralization stimulation or suppression, respectively) and magnitude varied with soil and biochar type, ranging from −52 to 89% at the end of 1 year. In general, C mineralization was greater than expected (positive priming) for soils combined with biochars produced at low temperatures (250 and 400 °C) and from grasses, particularly during the early incubation stage (first 90 d) and in soils of lower organic C content. It contrast, C mineralization was generally less than expected (negative priming) for soils combined with biochars produced at high temperatures (525 and 650 °C) and from hard woods, particularly during the later incubation stage (250-500 d). Measurements of the stable isotopic signature of respired CO 2 indicated that, for grass biochars at least, it was predominantly pyrogenic C mineralization that was stimulated during early incubation and soil C mineralization that was suppressed during later incubation stages. It is hypothesized that the presence of soil OM stimulated the co-mineralization of the more labile components of biochar over the short term. The data strongly suggests, however, that over the long term, biochar-soil interaction will enhance soil C storage via the processes of OM sorption to biochar and physical protection. 相似文献
14.
N mineralization capacity and its main controlling factors were studied in a large variety ( n=112) of native (forest, bush) and agricultural (pasture, cultivated) soils from several climatic zones in Spain. The available inorganic N content, net N mineralization, and net N mineralization rate were determined after 6 weeks of aerobic incubation. NH
inf4
sup+
–N largely predominated over NO
inf3
sup-
-N (ratio near 10:1) except in some agricultural soils. Net N mineralization predominated (83% of soils) over net N immobilization, which was more frequent in agricultural soils (25%) than in native soils (9%). In forest soils, both net N mineralization and the net N mineralization rate were significantly higher than in the other soil groups. The net N mineralization rate of pasture and cultivated soils was similar to that of bush soils, but available inorganic N was lower. The net N mineralization rate decreased in the order: soils over acid rocks>soils over sediments>soils over basic rocks or limestone; moreover, the highest net N mineralization and available inorganic N were found in soils over acid rocks. The highest N mineralization was found in soils with low C and N contents, particularly in the native soils, in which N mineralization increased as the C:N ratio increased. N mineralization was higher in soils with a low pH and base saturation than in soils with high pH and base saturation values, which sometimes favoured N immobilization. Soils with an Al gel content of >1% showed lower net N mineralization rates than soils with Al gel contents of <1%, although net N mineralization and available inorganic N did not differ between these groups. The net N mineralization rate in silty soils was significantly lower than in sandy and clayey soils, although soil texture only explained a low proportion of the differences in N mineralization between soils. 相似文献
15.
The relationships between soil microbial properties and fine root decomposition processes under elevated CO 2 are poorly understood. To address this question, we determined soil microbial biomass carbon (SMB-C) and nitrogen (SMB-N), enzymes related to soil carbon (C) and nitrogen (N) cycling, the abundance of cultivable N-fixing bacteria and cellulolytic fungi, fine root organic matter, lignin and holocellulose decomposition, and N mineralization from 2006 to 2007 in a Mongolian oak ( Quercus mongolica Fischer ex Ledebour) ecosystem in northeastern China. The experiment consisted of three treatments: elevated CO 2 chambers, ambient CO 2 chambers, and chamberless plots. Fine roots had significantly greater organic matter decomposition rates under elevated CO 2. This corresponded with significantly greater SMB-C. Changes in the activities of protease and phenol oxidase under elevated CO 2 could not explain the changes in fine root N release and lignin decomposition rates, respectively, while holocellulose decomposition rate had the same response to experimental treatments as did cellulase activity. Changes in cultivable N-fixing bacterial and cellulolytic fungal abundances in response to experimental treatments were identical to those of N mineralization and lignin decomposition rates, respectively, suggesting that the two indices were closely related to fine root N mineralization and lignin decomposition. Our results showed that the increased fine root organic matter, lignin and holocellulose decomposition, and N mineralization rates under elevated CO 2 could be explained by shifts in SMB-C and the abundance of cellulolytic fungi and N-fixing bacteria. Enzyme activities are not reliable for the assessment of fine root decomposition and more attention should be given to the measurement of specific bacterial and fungal communities. 相似文献
16.
In a short-term laboratory study C mineralization potentials were determined on soil samples obtained from some representative agricultural soils in Tuscany, Italy. All the kinetic models tested to describe the mineralization process provided a good fit to the experimental data. A modified first-order model best described C mineralization in the soil. Both potentially mineralizable C and the mineralization rate ( k) varied considerably among soils, reflecting the differences in soil properties. Potentially mineralizable C was positively related to C evolved as CO 2 and to the exchange capacity. Normalized values (potentially mineralizable C divided by organic C), representing on average about 2% of the total soil C, was positively correlated to soil pH and negatively to the soil C pool, the soil N pool, and total microbial activity. Values for k ranged between 0.050 and 0.104 day -1, being higher in fine-textured soils and in soils with a large free Fe content. A low C:N ratio was indicative of a high k value. Turnover times for mineralized C were relatively rapid, ranging from 10 to 20 days. 相似文献
17.
The effects of soil mesofauna and different farming systems on decomposition of clover ( Trifolium repens) litter were investigated in a laboratory experiment. Microcosms were incubated for 16 weeks with fine and coarse litterbags in soils from three types of management systems: fallow, integrated farming and organic farming, the latter two cropped with wheat. The effects were studied by analysing litter mass loss, C and N content, DOC, nitrate and pH in soil leachate, and CO 2 production, as well as mesofauna. Mesofauna significantly accelerated mass loss and C and N release from clover litter in all three soils. With mesofauna access, at the end of the experiment average clover mass loss was almost twice as high and clover C and N content were 60% lower than without mesofauna. Farming systems influenced the decomposition through affecting both element turnover and mesofauna. Although in the first weeks less N was leached from organic farming than from integrated farming soil, cumulative N leaching did not differ between these soils. However, more than 20% less N was leached from the fallow soil than from the field soils. CO 2 production was highest in fallow soil. Here, mesofauna had no effect on this variable. In soil with integrated farming, mesofauna reduced cumulative CO 2 production by 10% whereas in soil from organic farming it increased CO 2 production by 20%. Our data suggest that differences in C and N turnover in different management systems are strongly mediated by soil mesofauna. 相似文献
18.
Periods of prolonged summer drought are likely to be expected for this century, with possibly strong effects on carbon (C) and nitrogen (N) mineralization in soils. Drought generally reduces mineralization rates, but the possibility of excess mineralization pulses during rewetting raises the question about the net effect of drying-rewetting events. In this experiment, we measured C and N mineralization in undisturbed soil columns that were either kept under continuously moist conditions (control) or that were subjected to drying-rewetting. We had three treatments (D1-D3) with different drying intensity (increasing from D1 to D3) but uniform rewetting intensity (4 mm d −1). Soil columns were taken from a Norway spruce forest in Bavaria, Germany. The CO 2 fluxes from control and treatment groups were identical before drying. Over the 80 d drought period, total CO 2 emissions from D1, D2, and D3 were only 72, 52 and 43% of that from the control, respectively. Rewetting resulted in a fast increase of CO 2 fluxes to approx. the same level as in the control. Rewetting could not restore soil moisture of the dry soil to the level of the control, presumably because of preferential flow and water repellency of soil organic matter. No significant excess C mineralization during the 40 d rewetting period was observed. Adding up total CO 2 fluxes during drought and rewetting period, the treatments D1, D2, and D3 emitted only 88, 71 and 67% of the CO 2 emitted by the control. Measurements of dissolved organic carbon (DOC) did only show minor differences between control and treatment columns, indicating that no significant accumulation of DOC took place during the drought period. Radiocarbon signature of emitted CO 2 indicated that C mineralization was reduced with decreasing water availability and no new substrate became bioavailable. Net N mineralization over the course of the whole experiment was reduced by drought to 77, 65 or 52% of the control. Net nitrification was virtually zero during drought whereas net ammonification continued at reduced levels. In summary, we found that drying-rewetting generally reduced C and N mineralization in this soil and that the total reduction increased with drought intensity. 相似文献
19.
We used a continuous labeling method of naturally 13C-depleted CO 2 in a growth chamber to test for rhizosphere effects on soil organic matter (SOM) decomposition. Two C3 plant species, soybean ( Glycine max) and sunflower ( Helianthus annus), were grown in two previously differently managed soils, an organically farmed soil and a soil from an annual grassland. We maintained a constant atmospheric CO 2 concentration at 400±5 ppm and δ 13C signature at −24.4‰ by regulating the flow of naturally 13C-depleted CO 2 and CO 2-free air into the growth chamber, which allowed us to separate new plant-derived CO 2-C from original soil-derived CO 2-C in soil respiration. Rhizosphere priming effects on SOM decomposition, i.e., differences in soil-derived CO 2-C between planted and non-planted treatments, were significantly different between the two soils, but not between the two plant species. Soil-derived CO 2-C efflux in the organically farmed soil increased up to 61% compared to the no-plant control, while the annual grassland soil showed a negligible increase (up to 5% increase), despite an overall larger efflux of soil-derived CO 2-C and total soil C content. Differences in rhizosphere priming effects on SOM decomposition between the two soils could be largely explained by differences in plant biomass, and in particular leaf biomass, explaining 49% and 74% of the variation in primed soil C among soils and plant species, respectively. Nitrogen uptake rates by soybean and sunflower was relatively high compared to soil C respiration and associated N mineralization, while inorganic N pools were significantly depleted in the organic farm soil by the end of the experiment. Despite relatively large increases in SOM decomposition caused by rhizosphere effects in the organic farm soil, the fast-growing soybean and sunflower plants gained little extra N from the increase in SOM decomposition caused by rhizosphere effects. We conclude that rhizosphere priming effects of annual plants on SOM decomposition are largely driven by plant biomass, especially in soils of high fertility that can sustain high plant productivity. 相似文献
20.
The roles of microbial biomass (MBC) and substrate supply as well as their interaction with clay content in determining soil respiration rate were studied using a range of soils with contrasting properties. Total organic C (TOC), water-soluble organic carbon, 0.5 M K 2SO 4-extractable organic C and 33.3 mM KMnO 4-oxidisable organic carbon were determined as C availability indices. For air-dried soils, these indices showed close relationship with flush of CO 2 production following rewetting of the soils. In comparison, MBC determined with the chloroform fumigation-extraction technique had relatively weaker correlation with soil respiration rate. After 7 d pre-incubation, soil respiration was still closely correlated with the C availability indices in the pre-incubated soils, but poorly correlated with MBC determined with three different techniques—chloroform fumigation extraction, substrate-induced respiration, and chloroform fumigation-incubation methods. Results of multiple regression analyses, together with the above observations, suggested that soil respiration under favourable temperature and moisture conditions was principally determined by substrate supply rather than by the pool size of MBC. The specific respiratory activity of microorganisms (CO 2-C/MBC) following rewetting of air-dried soils or after 7 d pre-incubation was positively correlated with substrate availability, but negatively correlated with microbial pool size. Clay content had no significant effect on CO 2 production rate, relative C mineralization rate (CO 2-C/TOC) and specific respiratory activity of MBC during the first week incubation of rewetted dry soils. However, significant protective effect of clay on C mineralization was shown for the pre-incubated soils. These results suggested that the protective effect of clay on soil organic matter decomposition became significant as the substrate supply and microbial demand approached to an equilibrium state. Thereafter, soil respiration would be dependent on the replenishment of the labile substrate from the bulk organic C pool. 相似文献
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