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1.
Tree species have significant effects on the availability and dynamics of soil organic matter. In the present study, the pool sizes of soil dissolved organic matter (DOM), potential mineralizable N (PMN) and bio-available carbon (C) (measured as cumulative CO2 evolution over 63 days) were compared in soils under three coniferous species — 73 year old slash (Pinus elliottii), hoop (Araucaria cunninghamii) and kauri (Agathis robusta) pines. Results have shown that dissolved organic N (DON) in hot water extracts was 1.5–1.7 times lower in soils under slash pine than under hoop and kauri pines, while soil dissolved organic C (DOC) in hot water extracts tended to be higher under slash pine than hoop and kauri pines but this was not statistically significant. This has led to the higher DOC:DON ratio in soils under slash pine (32) than under hoop and kauri pines (17). Soil DOC and DON in 2 M KCl extracts were not significantly different among the three tree species. The DOC:DON ratio (hot water extracts) was positively and significantly correlated with soil C:N (R2 = 0.886, P < 0.01) and surface litter C:N ratios (R2 = 0.768, P < 0.01), indicating that DOM was mainly derived from litter materials and soil organic matter through dissolution and decomposition. Soil pH was lower under slash pine (4.5) than under hoop (6.0) and kauri (6.2) pines, and negatively correlated with soil total C, C:N ratio, DOC and DOC:DON ratio (hot water extracts), indicating the soil acidity under slash pine favored the accumulation of soil C. Moreover, the amounts of dissolved inorganic N, PMN and bio-available C were also significantly lower in soils under slash pine than under hoop and kauri pines. It is concluded that changes in the quantity and quality of surface litters and soil pH induced by different tree species largely determined the size and quality of soil DOM, and plantations of hoop and kauri pine trees may be better in maintaining long-term soil N fertility than slash pine plantations.  相似文献   

2.
The aim of this study was to compare the effects of silver birch (Betula pendula Roth) and Norway spruce (Picea abies (L.) Karst.) on soil C and N transformations and on the characteristics of organic matter. Soil samples were taken from the humus layer of a replicated 35-year-old birch-spruce field experiment growing on Vaccinium myrtillus site type in middle-eastern Finland. The soil was a podzol and humus type mor. Soil pH was higher under birch (4.7) than under spruce (4.1). The C-to-N ratio was lower under birch (17) than under spruce (23). Per unit organic matter, microbial biomass C and N, net N mineralization and net nitrification were all higher in birch soil than in spruce soil. The rate of C mineralization (CO2 production) was, however, the same regardless of tree species. Water-extracts were analyzed for the concentrations of dissolved organic C (DOC) and N (DON) and characterized according to molecular size distribution by ultrafiltration and according to chemical composition using a resin fractionation technique. The concentration of DON, in particular, was higher in birch soil than in spruce soil. The distribution of DOC and DON into different fractions based on molecular size or chemical composition was rather similar in both soils. The concentration of total phenolics, expressed as tannic acid equivalents, was higher in the humus layer under birch than in the humus layer under spruce, because the birch humus layer contained significantly more low-molecular weight (about <0.5 kD) phenolics than the spruce humus layer did. The concentration of proanthocyanidins (condensed tannins) was higher in spruce soil than in birch soil. The concentrations of the five most abundant phenolic acids showed that ferulic and p-coumaric acids were more abundant in spruce soil. Birch soil tended to contain slightly more nonvolatile sesquiterpenes than the spruce soil. The concentration of diterpenes was similar in both soils; but birch soil contained significantly more triterpenes, mainly sterols, than spruce soil did.  相似文献   

3.
Dissolved organic nitrogen (DON) plays a key role in the N cycle of many ecosystems, as DON availability and biodegradation are important for plant growth, microbial metabolism and N transport in soils. However, biodegradation of DON (defined as the sum of mineralization and microbial immobilization) is only poorly understood. In laboratory incubations, biodegradation of DON and dissolved organic carbon (DOC) from Oi and Oa horizons of spruce, beech and cypress forests ranged from 6 to 72%. Biodegradation of DON and DOC was similar in most samples, and mineralization of DON was more important than microbial immobilization. Nitrate additions (0-10 mg N L−1) never influenced either DON immobilization by microorganisms or mineralization. We conclude that soil microorganisms do not necessarily prefer mineral N over DON for meeting their N demand, and that biodegradation of DON seems to be driven by the microbial demand for C rather than N. Quantifying the dynamics of DON in soils should include consideration of both C and N demands by microbes.  相似文献   

4.
The degradability and chemical characteristics of dissolved organic carbon (DOC) and nitrogen (DON) from the litter, F and H layers of silver birch (Betula pendula Roth), Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.) stands were studied in an incubation experiment. Soil dissolved organic matter (DOM) was collected by centrifugation. Degradability was assessed in an incubation experiment by measuring the loss of DOC and DON, the mineralization rate of DOC and the availability of DOM to both bacteria and fungi, and by estimating the proportion of labile DOC of the total DOC. The degradability of DOC was highest in the litter layer and in that layer under birch. In the F and H layers, however, the degradability was highest under spruce. The most degradable fractions were the hydrophilic neutral fraction of DOC, the hydrophilic base fraction of DON, and the phenol fraction, as well as the smallest (<1 kDa) and largest (>100 kDa) molecular size classes of both DOC and DON. The degradability of these fractions seemed to be related to their relatively low C-to-N ratios. The hydrophilic acid fraction and the molecular size class of 1-10 kDa were more abundant in the H layer than in the litter layer, and thus apparently indicating a more decomposed DOM. In general, the effect of tree species on DOM was more obvious in the litter layer than in the lower organic layers.  相似文献   

5.
《Soil biology & biochemistry》2001,33(7-8):1113-1121
In this study, the influence of temperature and vegetation cover on soluble inorganic and organic nitrogen in a spodosol from north east Scotland was investigated. Firstly, soil cores were incubated at 5, 10 and 15°C for up to 8 weeks. Net mineralisation was observed at all temperatures with larger rates observed at higher temperatures. In contrast, water extractable dissolved organic nitrogen (DON) displayed no clear trend with time and showed little response to temperature. Secondly, intact cores of the same soil, with and without vegetation, were leached with artificial rain for 6 weeks at 6.5 and 15°C. Temperature and the presence of vegetation interacted to have a significant (P<0.01) effect on the concentration of NO3− in leachates; highest concentrations were observed in leachates from cores without vegetation at 15°C, whereas lowest concentrations were observed in leachates from cores with vegetation at 6.5°C. In contrast, concentrations of DON and dissolved organic carbon (DOC) were significantly (P<0.001) higher in leachates from cores with vegetation than without vegetation and were not affected by temperature. The cumulative amounts of DON and DOC leached from the cores with vegetation were 4 and 2.5 times greater, respectively, than those leached from the cores without vegetation. Comparison of soil solution (extracted by centrifugation at 0–5 and 5–10 cm depth) after leaching for 6 weeks, showed that the upper layer contained more than twice the amount of DON than the 5–10 cm layer and that the difference in concentration between the two depths was enhanced in the presence of vegetation. The results indicate that vegetation is an important source of DON and DOC. However, the removal of vegetation did not lead to an increase in the quantity of total dissolved nitrogen (TDN) in soil water, but resulted in a change in the dominant N fraction from DON to NO3−. In addition, the results show that DON, in both the incubated and leached cores, did not change as inorganic N was mineralised. This suggests that if water extractable DON was acting as a source of NH4+ or NO3−, then it was being replenished by, and in equilibrium with, a large reserve of organic N. Evidence of such a pool was indirect in the form of additional DON (equivalent to 2 g N m−2) being extracted by 0.5 M K2SO4.  相似文献   

6.
《Applied soil ecology》2006,31(1-2):53-61
Two soils from a secondary tropical forest at La Union, Philippines, predominantly vegetated with Swietenia marcrophylla and Gmelina arborea were amended with different leaf litter types (Eucalyptus camaldulensis, S. macrophylla, G. arborea, and Calliandra calothyrsus) and incubated in the laboratory for 49 days at 25 °C. The experiment was carried out to elucidate the reasons for a low ATP-to-microbial biomass C ratio and a high microbial biomass C-to-N ratio. This has been measured repeatedly in tropical forest soils. In the non-amended soils, the microbial biomass C-to-N ratio of 12.1 exceeded the soil organic C-to-total N ratio of 11, while the ergosterol-to-microbial biomass C ratio of 0.14% and the ATP-to-microbial biomass C ratio of 4.1 μmol g−1 were both low. At the end of the incubation, the addition of the different leaf litter types led generally to a decrease in the microbial biomass C-to-N ratio and to an increase in the ATP-to-microbial biomass C ratio, adenylate energy charge (AEC) and especially to an increase in the ergosterol-to-microbial biomass C ratio. The increase in the ATP-to-microbial biomass C ratio and the decrease in the microbial biomass C-to-N ratio were positively related to the N concentration in the leaf litter, the increase in the ergosterol-to-microbial biomass ratio negatively. The reasons for a low ATP-to-microbial biomass C ratio and a high microbial biomass C-to-N ratio are P deficiency and probably a reduced access of soil microorganisms to N containing organic components at low soil organic C levels.  相似文献   

7.
We conducted a laboratory incubation of forest (Scots pine (Pinus sylvestris) or beech (Fagus sylvatica)), grassland (Trifolium repens/Lolium perenne) and arable (organic and conventional) soils at 5 and 25 °C. We aimed to clarify the mechanisms of short-term (2-weeks) nitrogen (N) cycling processes and microbial community composition in relation to dissolved organic carbon (DOC) and N (DON) availability and selected soil properties. N cycling was measured by 15N pool dilution and microbial community composition by denaturing gradient gel electrophoresis (DGGE), phospholipid fatty acid (PLFA) and community level physiological profiles (CLPP). Soil DOC increased in the order of arable<grassland<forest soil while DON and gross N fluxes increased in the order of forest<arable<grassland soil; land use had no affect on respiration rate. Soil DOC was lower, while respiration, DON and gross N fluxes were higher at 25 than 5 °C. Gross N fluxes, respiration and bacterial biomass were all positively correlated with each other. Gross N fluxes were positively correlated with pH and DON, and negatively correlated with organic matter, fungal biomass, DOC and DOC/DON ratio. Respiration rate was positively correlated with bacterial biomass, DON and DOC/DON ratio. Multiple linear modelling indicated that soil pH, organic matter, bacterial biomass, DON and DOC/DON ratio were important in predicting gross N mineralization. Incubation temperature, pH and total-C were important in predicting gross nitrification, while gross N mineralization, gross nitrification and pH were important in predicting gross N immobilization. Permutation multivariate analysis of variance indicated that DGGE, CLPP and PLFA profiles were all significantly (P<0.05) affected by land use and incubation temperature. Multivariate regressions indicated that incubation temperature, pH and organic matter content were important in predicting DGGE, CLPP and PLFA profiles. PLFA and CLPP were also related to DON, DOC, ammonium and nitrate contents. Canonical correlation analysis showed that PLFA and CLPP were related to differences in the rates of gross N mineralization, gross nitrification and soil respiration. Our study indicates that vegetation type and/or management practices which control soil pH and mediate dissolved organic matter availability were important predictors of gross N fluxes and microbial composition in this short-term experiment.  相似文献   

8.
Effects of large-scale weed invasion on the nature and magnitude of moisture-pulse-driven soil processes in semiarid ecosystems are not clearly understood. The objective of this study was to monitor carbon dioxide (CO2) and nitrous oxide (N2O) emissions and changes in soil carbon (C) and nitrogen (N) following the application of a water pulse in Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) communities dominated by the exotic annual grass cheatgrass (Bromus tectorum) and by the native perennial grass western wheatgrass (Pascopyrum smithii). Sampling locations were established in shrub interspaces dominated by B. tectorum and P. smithi and beneath shrub canopies adjacent to interspaces dominated by B. tectorum and P. smithi, where no grass was present. Soils were classified as fine-loamy, mixed, Borollic Haplargids. Soil samples (0–10 cm) and air samples were collected at 0, 4, 8, 24, 49, 72, and 216 h following additions of 25.4 mm of water. Soil samples were analyzed for dissolved organic carbon (DOC), microbial biomass carbon (MBC), extractable ammonia (NH4+), extractable nitrate (NO3?), and dissolved organic nitrogen (DON). Grass species induced differences in soil nitrification, N2O and CO2 emissions, and the quantity and timing of labile C available to microbial populations responding to increased moisture availability. In the first 8-h phase after wetting P. smithii soils had the greatest CO2 emissions compared to other soils but B. tectorum soils had the greatest N2O emissions and the greatest increases in CO2 emissions relative to before wetting. Microbial biomass C in B. tectorum interspace soils increased rapidly but the response was short-lived despite sufficient water availability. After the first 8 h of soil response to wetting, the observed MBC declines in B. tectorum interspace coincided with disproportional DOC and DON concentration increases. Similar DOC and DON increases were also observed in B. tectorum soils beneath shrub canopy. In contrast, DOC and DON concentrations in P. smithii soils remained unaffected by soil wetting and small MBC increases observed during the first 8-h phase did not decline as rapidly as in B. tectorum interspace soils. In conclusion, summer drying-wetting cycles that occur frequently in areas invaded by B. tectorum can accelerate rates of nitrification and C mineralization, and contribute significantly to trace gas emissions from sagebrush-steppe grasslands. With frequent summer rainfall events, the negative consequences B. tectorum presence in the ecosystem can be significant.  相似文献   

9.
 The aims of this study were to characterize dissolved soil organic N (DON) and C (DOC) in a coniferous stand and an adjacent clear-cut, and to evaluate the importance of DON in N leaching. The study was carried out in a Norway spruce stand and a clear-cutting treatment in the same forest stand. Concentrations of DON in soil solution were monitored for 5 years after clear-cutting with gravity lysimeters. In the Norway spruce stand DON comprised 62–83% of the total N in soil solution over the 5-year period. The concentrations of DON in the clear-cut were higher than in the forest stand, but the proportion of total N was lower. To characterize dissolved organic matter, soil samples were aerobically incubated for 6 weeks in the laboratory, and the quantity, molecular size distribution and chemical nature of both DON and DOC were determined from water extracts made before and after the incubation. In the soil samples from the Norway spruce stand, C-rich compounds with a high C/N ratio and large molecular size were formed. In contrast, after the incubation the major carriers of DON in soil samples from the clear-cut were N-rich organic compounds with a low C/N ratio and a small molecular size. The distribution of different chemical fractions of DOC in soil did not differ much whether recovered from the Norway spruce stand or the clear-cut. It was (from highest to lowest concentration): hydrophobic acids>hydrophilic acids>phenols>hydrophilic neutrals. A major part of DON was also carried by these fractions. During incubation the concentration of N-containing hydrophilic acids increased, especially in the soil from the clearcut. In soil samples from the Norway spruce stand, the rate of net N mineralization was low and no NO3 was formed, whilst the rate of net N mineralization was high and net nitrification was intensive in soil from the clear-cut. Received: 12 June 2000  相似文献   

10.
We studied the effect of no-till (disc seeder), conventional-till (tine scarifier+disc seeder) and rotary-till (rotary hoe+disc seeder) management on soil organic matter (SOM) components, rates of carbon (C) and nitrogen (N) cycling, substrate utilization and microbial community composition. We hypothesized that labile SOM fractions are sensitive to changes in tillage techniques and, in turn mediate any tillage-induced changes in microbial function and composition. A replicated field site was established in May 1998 in the semi-arid agricultural region of Western Australia and soils were collected in September 2004. We found soil pH varied between different tillage techniques as an initial lime application was mixed to deeper soil depths in rotary-till soil than no-till and conventional-till soil. Total-C was greater in surface soil and lower in subsurface soil from no-till and conventional-till plots than from rotary-till plots, but there was no effect of tillage technique on total-C when averaged across soil depths. Light (specific density <1.0 g cm?3) fraction organic matter (LFOM), dissolved organic matter (DOM) and microbial biomass (MB) C and N pools, and rates of C and N cycling all tended to decrease with soil depth. In general, LFOM-C and N, dissolved organic C (DOC) and microbial biomass carbon (MB-C), soil respiration, cellulase activity, gross immobilization rates were positively correlated (r>0.50) and were greater in no-till and conventional-till soil than rotary-till soil both within, and across soil depths. These soil variables generally increased (r>0.5) with increasing soil pH. Dissolved organic N and gross N mineralization were positively correlated (r>0.90) but neither was affected by tillage techniques. No-till soil had greater utilization of carboxylic acids and lower utilization of amino acids and carbohydrates than conventional-till and rotary-till soil; surface soil also had greater utilization of carboxylic acids than subsurface soil. In turn, substrate utilization differed between soil depths, and between no-till soil and conventional-till and rotary-till soil; these differences were correlated with soil pH, total-N, DOC, LFOM-N and microbial biomass nitrogen (MB-N). Bacterial and fungal biomasses generally decreased with soil depth and were greater in no-till and conventional-till soil than rotary-till soil. Microbial community composition differed between all tillage techniques and soil depths; these differences were correlated with soil textural classes, soil pH, and total, LFOM, DOM and microbial C and N pools. These results indicate that most tillage-induced changes to soil properties were associated with the greater soil disturbance under rotary-till than under no-till or conventional-till management. Our results indicate that tillage-induced changes to soil pH, and LFOM, DOM and microbial biomass pools are likely to be important regulators of the rates of C and N cycling, substrate utilization and microbial community composition in this coarse textured soil.  相似文献   

11.
Because dissolved organic matter (DOM) plays an important role is terrestrial C-, N- and P-balances and transport of these three components to aquatic environments, there is a need to include it in models. This paper presents the concept of the newly developed DOM modules implemented in the DAISY model with focus on the quantification of DOM sorption/desorption and microbial-driven DOM turnover. The kinetics of DOM sorption/desorption is described by the deviation of the actual DOM concentration in solution from the equilibrium concentration, Ceq. The Ceq is soil specific and estimated from pedotransfer functions taking into account the soil content of organic matter, Al and Fe oxides. The turnover of several organic matter pools including one DOM pool are described by first-order kinetics.The DOM module was tested at field scale for three soil treatments applied after cultivating grass–clover swards. Suction cups were installed at depths 30, 60 and 90 cm and soil solution was sampled for quantification of dissolved organic C (DOC) and dissolved organic N (DON). In the topsoil, the observed fluctuations in DOC were successfully simulated when the sorption/desorption rate coefficient k was low. In the subsoil, the observed concentrations of DOC were steadier and the best simulations were obtained using a high k. The model shows that DOC and DON concentrations are levelled out in the subsoils due to soil buffering. The steady concentration levels were based on the Ceq for each horizon and the kinetic concept for sorption/desorption of DOC appeared a viable approach. If Ceq was successfully estimated by the pedotransfer function it was possible to simulate the DOC concentration in the subsoil. In spite of difficulties in describing the DOC dynamics of the topsoil, the DOM module simulates the subsoil concentration level of DOC well, and also—but with more uncertainty—the DON concentration level.  相似文献   

12.
Polar ecosystems are currently experiencing some of the fastest rates of climate warming. An increase in soil temperature in High Arctic regions may stimulate soil permafrost melting and microbial activity, thereby accelerating losses of greenhouse gases. It is therefore important to understand the factors regulating the rates of C turnover in polar soils. Consequently, our aims were to: (1) assess the concentration of low molecular weight (MW) dissolved organic carbon (DOC) in soil, (2) to investigate the temperature-dependent turnover of specific low MW compounds, and (3) to analyse the influence of substrate concentration on C cycling. Microbial mineralisation of labile low MW DOC in two High Arctic tundra soils was investigated using soil solutions spiked with either 14C-labelled glucose or amino acids. Spiked solutions were added to the top- and sub-soil from two ecosystem types (lichen and Carex dominated tundra), maintained at three temperatures (4–20 °C), and their microbial mineralisation kinetics monitored. 14CO2 evolution from the tundra soils in response to 14C-glucose and -amino acid addition could best be described by a double first order exponential kinetic equation with rate constants k1 and k2. Both forms of DOC had a short half-life (t1/2) in the pool of microbial respiratory substrate (t1/2 = 1.07 ± 0.10 h for glucose and 1.63 ± 0.14 h for amino acids; exponential coefficient k1 = 0.93 ± 0.07 and 0.64 ± 0.06 h?1 respectively) whilst the second phase of mineralisation, assumed to be C that had entered the microbial biomass, was much slower (average k2 = 1.30 × 10?3 ± 0.49 × 10?4 h?1). Temperature had little effect on the rate of mineralisation of 14C used directly as respiratory substrate. In contrast, the turnover rate of the 14C immobilized in the microbial biomass prior to mineralisation was temperature sensitive (k2 values of 0.99 × 10?3 h?1 and 1.66 × 10?3 h?1 at 4 and 20 °C respectively). Concentration-dependent glucose and amino acid mineralisation kinetics of glucose and amino acids (0–10 mM) were best described using Michaelis–Menten kinetics; there was a low affinity for both C substrates by the microbial community (Km = 4.07 ± 0.41 mM, Vmax = 0.027 ± 0.005 mmol kg?1 h?1). In conclusion, our results suggest that in these C limiting environments the flux of labile, low MW DOC through the soil solution is extremely rapid and relatively insensitive to temperature. In contrast, the turnover of C incorporated into higher molecular weight microbial C pools appears to show greater temperature sensitivity.  相似文献   

13.
《Applied soil ecology》2011,47(3):413-421
Substrate input as well as climatic factors affect C and N cycling and microbial properties in forest soils. We used a microcosm approach to investigate the response of CO2 efflux, net N mineralization, and microbial community-level physiological profile (CLPP) to temperature (5 vs. 15 °C) and substrate (with and without sucrose addition) addition in surface mineral soils collected from 4-, 6-, 13-, and 15-year old (ages in 2007) hybrid poplar (Populus deltoides × Populus × petrowskyana var. Walker) stands in northern Alberta. In the early stage of incubation (0–2 h), CO2 efflux was higher at 5 °C than at 15 °C with little effect from substrate addition, while 24 h after the addition of substrate, CO2 efflux became higher under the 15 °C incubation. After 72 h incubation, temperature and substrate addition effects on CO2 efflux subsided and CO2 efflux rates tended to converge among the treatments. Net N mineralization was significantly affected by substrate addition and stand age, while rates of net ammonification were higher at 5 °C than at 15 °C. Net N mineralization occurred without sucrose addition while net immobilization occurred with sucrose addition. The soil from the youngest stand had the lowest N mineralization rate among the stands for each corresponding substrate-incubation temperature treatment. We used Ecoplates from Biolog™ to study sole-carbon-source-utilization profiles of microbial communities at the end of the incubation. Principal component analysis of C utilization data separated microbial communities with respect to substrate addition, incubation temperature and stand age. Our data showed that organic matter mineralization and microbial substrate utilization were affected by incubation temperature, substrate availability and stand age, indicating that the responses of microbial communities in the studied hybrid poplar plantations to temperature changes were strongly mediated by labile C availability and stand development.  相似文献   

14.
有机物料输入稻田提高土壤微生物碳氮及可溶性有机碳氮   总被引：27，自引：6，他引：27  
土壤微生物量碳、氮和可溶性有机碳、氮是土壤碳、氮库中最活跃的组分,是反应土壤被干扰程度的重要灵敏性指标,通过设置相同有机碳施用量下不同有机物料处理的田间试验,研究了有机物料添加下土壤微生物量碳（soil microbial biomass carbon,MBC）、氮（soil microbial biomass nitrogen,MBN）和可溶性有机碳（dissolved organic carbon,DOC）、氮（dissolved organic nitrogen,DON）的变化特征及相互关系。结果表明化肥和生物碳、玉米秸秆、鲜牛粪或松针配施下土壤微生物量碳、氮和可溶性有机碳、氮显著大于不施肥处理（no fertilization,CK）和单施化肥处理,分别比不施肥处理和单施化肥平均高23.52%和12.66%（MBC）、42.68%和24.02%（MBN）、14.70%和9.99%（DOC）、22.32%和21.79%（DON）。化肥和有机物料配施处理中,化肥+鲜牛粪处理的微生物量碳、氮和可溶性有机碳、氮最高,比CK高26.20%（MBC）、49.54%（MBN）、19.29%（DOC）和32.81%（DON）,其次是化肥+生物碳或化肥+玉米秸秆处理,而化肥+松针处理最低。土壤可溶性有机碳质量分数（308.87 mg/kg）小于微生物量碳（474.71 mg/kg）,而可溶性有机氮质量分数（53.07 mg/kg）要大于微生物量氮（34.79 mg/kg）。与不施肥处理相比,化肥和有机物料配施显著降低MBC/MBN和DOC/DON,降低率分别为24.57%和7.71%。MBC和DOC、MBN和DON随着土壤有机碳（soil organic carbon,SOC）、全氮（total nitrogen,TN）的增加呈显著线性增加。MBC、MBN、DOC、DON、DOC+MBC和DON+MBN之间呈极显著正相关（P<0.01）。从相关程度看,DOC+MBC和DON+MBN较MBC、DOC、MBN、DON更能反映土壤中活性有机碳和氮库的变化,成为评价土壤肥力及质量的更有效指标。结果可为提高洱海流域农田土壤肥力,增强土壤固氮效果,减少土壤中氮素流失,保护洱海水质安全提供科学依据。  相似文献   

15.
《Applied soil ecology》2007,35(1):247-255
Seasonally snow-covered alpine soils may be subjected to freeze/thaw cycles, particularly during years having little snow and during the late winter and early spring periods. Freeze/thaw cycles can stimulate soil mineralization and could therefore be one factor regulating nitrogen (N) and phosphorus (P) availability and cycling. In this study laboratory incubation experiments using four soils having contrasting properties have been used to characterize the change in N and P forms (microbial and soluble inorganic/organic) that occur after simulated freeze/thaw cycles.Soil samples were collected from locations representing extreme examples of either direct human management (grazed meadow (site M) and extensive grazing beneath larch (site L)) or those disturbed by more natural events (recent avalanche and colonisation by alder (site A)) and from beneath the expected forest climax vegetation beneath fir (site F). Topsoil from these sites, maintained at two different water contents (20 and 30%, w/w), were exposed to either a single (SF) or four sequential (4SF) freeze/thaw cycles. Each cycle consisted of 12 h at −9 °C and 12 h at +4 °C mimicking a diurnal pattern.A SF cycle reduced microbial N for soils from sites F and A and was accompanied by a significant increase in dissolved organic nitrogen (DON) at both moisture contents. In contrast, the microbial N of soils from M and L was not affected by the freeze/thaw cycles, suggesting a particular adaptation of soil microbes to these extremes in temperature. Freeze/thaw cycles resulted in a significant increase in the net ammonification in all soils.Extractable total dissolved N (TDN) and total dissolved P (TDP) increased in all soils after a SF cycle, however, the relative importance of the different N and P forms differed. At the lower soil moisture content, NO3− concentrations remained constant or slightly decreased in all soils, except that from site M. In all other soils DON appeared to replace NO3− as the potentially mobile N source after the freeze/thaw cycles. The relative contribution of dissolved organic P to TDP after freeze/thaw remained significant, and greater than 50% in all soils.Freeze/thaw cycles, in seasonally snow covered soils, are likely to have a selective effect on the microbial biomass. Freezing and thawing resulted in a pulse of net ammonification and DON release, which represent an important influence upon N cycling in these alpine systems.  相似文献   

16.
Dissolved organic matter (DOM) is important for the cycling and transport of carbon (C) and nitrogen (N) in soil. In temperate forest soils, dissolved organic N (DON) partly escapes mineralization and is mobile, promoting loss of N via leaching. Little information is available comparing DOC and DON dynamics under tropical conditions. Here, mineralization is more rapid, and the demand of the vegetation for nutrients is larger, thus, leaching of DON could be small. We studied concentrations of DOC and DON during the rainy seasons 1998–2001 in precipitation, canopy throughfall, pore water in the mineral soil at 5, 15, 30, and 80 cm depth, and stream water under different land‐use systems representative of the highlands of northern Thailand. In addition, we determined the distribution of organic C (OC) and N (ON) between two operationally defined fractions of DOM. Samples were collected in small water catchments including a cultivated cabbage field, a pine plantation, a secondary forest, and a primary forest. The mean concentrations of DOC and DON in bulk precipitation were 1.7 ± 0.2 and 0.2 ± 0.1 mg L–1, respectively, dominated by the hydrophilic fraction. The throughfall of the three forest sites became enriched up to three times in DOC in the hydrophobic fraction, but not in DON. Maximum concentrations of DOC and DON (7.9–13.9 mg C L–1 and 0.9–1.2 mg N L–1, respectively) were found in samples from lysimeters at 5 cm soil depth. Hydrophobic OC and hydrophilic ON compounds were released from the O layer and the upper mineral soil. Concentrations of OC and ON in mineral‐soil solutions under the cabbage cultivation were elevated when compared with those under the forests. Similar to most temperate soils, the concentrations in the soil solution decreased with soil depth. The reduction of OC with depth was mainly due to the decrease of hydrophobic compounds. The changes in OC indicated the release of hydrophobic compounds poor in N in the forest canopy and the organic layers. These substances were removed from solution during passage through the mineral soil. In contrast, organic N related more to labile microbial‐derived hydrophilic compounds. At least at the cabbage‐cultivation site, mineralization seemed to contribute largely to the decrease of DOC and DON with depth, possibly because of increased microbial activity stimulated by the inorganic‐N fertilization. Similar concentrations and compositions of OC and ON in subsoils and streams draining the forested catchments suggest soil control on stream DOM. The contribution of DON to total dissolved N in those streams ranged between 50% and 73%, underscoring the importance of DOM for the leaching of nutrients from forested areas. In summary, OC and ON showed differences in their dynamics in forest as well as in agricultural ecosystems. This was mainly due to the differing distribution of OC and ON between the more immobile hydrophobic and the more easily degradable hydrophilic fraction.  相似文献   

17.
Dissolved organic matter (DOM) plays a central role in driving biogeochemical processes in soils, but little information is available on the relation of soil DOM dynamics to microbial activity. The effects of NO3− and NH4+ deposition in grasslands on the amount and composition of soil DOM also remain largely unclear. In this study, a multi-form, low-dose N addition experiment was conducted in an alpine meadow on the Qinghai–Tibetan Plateau in 2007. Three N fertilizers, NH4Cl, (NH4)2SO4 and KNO3, were applied at four rates: 0, 10, 20 and 40 kg N ha−1 yr−1. Soil samples from surface (0–10 cm) and subsurface layers (10–20 cm) were collected in 2011. Excitation/emission matrix fluorescence spectroscopy (EEM) was used to assess the composition and stability of soil DOM. Community-level physiological profile (CLPP, basing on the BIOLOG Ecoplate technique) was measured to evaluate the relationship between soil DOC dynamics and microbial utilization of C resources. Nitrogen (N) dose rather than N form significantly increased soil DOC contents in surface layer by 23.5%–35.1%, whereas it significantly decreased soil DOC contents in subsurface layer by 10.4%–23.8%. Continuous five-year N addition significantly increased the labile components and decreased recalcitrant components of soil DOM in surface layer, while an opposite pattern was observed in subsurface layer; however, the humification indices (HIX) of soil DOM was unaltered by various N treatments. Furthermore, N addition changed the amount and biodegradability of soil DOM through stimulating microbial metabolic activity and preferentially utilizing organic acids. These results suggest that microbial metabolic processes dominate the dynamics of soil DOC, and increasing atmospheric N deposition could be adverse to the accumulation of soil organic carbon pool in the alpine meadow on the Qinghai-Tibetan Plateau.  相似文献   

18.
The aim of this study was to investigate how three vascular plant species (Calluna vulgaris, Eriophorum angustifolium and Eriophorum vaginatum) colonising an abandoned cutover peatland affect fluxes of recent photosynthate to dissolved organic carbon (DOC), soil and plant respiration and shoot biomass. We used in situ 13CO2 pulse labelling to trace carbon (C) throughout a 65 day pulse chase period. Between 16 and 35% of the pulse of 13C remained in shoot biomass after 65 days with significant differences between C. vulgaris and E. angustifolium (P = 0.009) and between C. vulgaris and E. vaginatum (P = 0.04). A maximum of 29% was detected in DOC beneath labelled plants and losses of 13C from peat respiration never exceeded 0.16% of the original pulse, showing that little newly fixed C was allocated to this pool. There were no significant differences between the different plant species with respect to 13C recovered from DOC or via peat respiration. More C was lost via shoot respiration; although amounts varied between the three plant species, with 4.94–27.33% of the 13C pulse respired by the end of the experiment. Significant differences in 13C recovered from shoot respiration were found between C. vulgaris and E. angustifolium (P = 0.001) and between E. angustifolium and E. vaginatum (P = 0.032). Analysis of δ13C of microbial biomass indicated that recently assimilated C was allocated to this pool within 1 day of pulse labelling but there were no significant differences in the 13C enrichment of the microbial biomass associated with the different plant species. The data suggest that peat respiration represents a small flux of recent assimilate compared to other fluxes and pools and that different vascular plant species show considerable variation in the quantities and dynamics of C allocated to DOC.  相似文献   

19.
The primary aim of the study was to determine the long-term (12 years) effects of leguminous cover crops like Atylosia scarabaeoides, Centrosema pubescens, Calopogonium mucunoides and Pueraria phaseoloides on important soil biochemical and biological properties and their interrelationships in the organic (fresh litter layer, F and fermented + humus layer, F + H) and mineral (0–10 and 10–20 cm) layers of soils of a 19-year-old coconut plantation.The total biomass production (above-ground) for the 12-year period varied significantly between the cover crops and ranged from 34.86 (calopo) to 90.43 (pueraria) Mg ha–1. Total N and C additions at the cover cropped (CC) site for the 12-year period were 0.97–3.07 Mg ha–1 and 16.90–43.34 Mg ha–1, respectively. Irrespective of layers, the levels of organic C, total N, organic substrates viz., dissolved organic C and N, labile organic N, water soluble carbohydrates, and light fraction organic matter-C and were markedly higher in the CC site compared to the control. Consequently, the levels of microbial biomass-C (CMIC), -N (NMIC) and -P (PMIC), net N mineralization rates, CO2 evolution, metabolic quotient (qCO2) and the activities of l-asparaginase, l-glutaminase and β-glucosaminidase were significantly higher in the CC site compared to the corresponding levels in the control site. Between layers, the levels of various chemical, biochemical and microbial parameters were consistently higher in the organic layers compared to the mineral layers at all the sites including control. Among the ratios of various microbial indices, the ratios of CMIC: organic C and CMIC: PMIC did not differ significantly between the layers and sites. However, the ratio of CMIC: NMIC was relatively higher in the mineral layers and control site. The variation in individual soil properties between layers and sites reflected the concomitant changes occurring in soil organic matter content. Apparently, microbial activity was limited by the supply of biologically available substrates in the mineral layers and the control site. Contrarily, the more direct supply of nutrients from decomposing plant litter and the indirect supply of nutrients from the mineralization of organic matter led to significantly higher levels of microbial biomass in the organic layers.  相似文献   

20.
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   

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