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1.
Leaching of dissolved organic matter (DOM) from pastoral soils is increasingly seen as an important but poorly understood process. This paper examined the relationship between soil chemical properties, microbial activity and the losses of dissolved organic carbon (DOC) and nitrogen (DON) through leaching from six pasture soils. These soils differed in carbon (C) (4.6–14.9%) and nitrogen (N) (0.4–1.4%) contents and in the amount of organic C and N that had accumulated or been lost in the preceding 20+ years (i.e. −5131 to +1624 kg C ha−1 year−1 and −263 to +220 kg N ha−1 year−1, respectively). The paper also examined whether between‐soil‐type differences in DOC and DON leaching was a major explanatory factor in the observed range of soil organic matter (SOM) changes in these soils. Between 280 and 1690 kg C ha−1 year−1 and 28–117 kg N ha−1 year−1 leached as DOC and DON, respectively, from the six soils in a lysimeter study, with losses being greater from two poorly drained gley soils. Losses of C and N of this magnitude, while at the upper end relative to published data, could not fully explain the losses at Rawerawe, Bruntwood and Lepperton sites reported by Schipper et al. (2007) . The study highlights the leaching of DOM as a significant pathway of loss of C and N in pasture soils that is often ignored or given little attention in predictive models and nutrient budgeting. Leaching losses of DOC and DON alone, or in combination with slightly increased respiration losses of SOM given a 0.2°C increase in the mean annual soil temperature, do not fully explain long‐term changes in the SOM observed at these sites. When soils examined in the present study were separated on the basis of drainage class, the losses of DOC by leaching were correlated with both total and hot‐water extractable C (HWC), the latter being a measure of the labile SOM fraction. Basal microbial CO2 respiration rates, which varied between 1 and 3.5 µg CO2‐C g−1 soil hour−1 in surface soils (0–75‐mm depth), was also linked to HWC and the quantities of C lost as DOC. Adoption of the HWC method as an approach that could be used as a proxy for the direct measurement of the soil organic C lost by leaching as DOC or respired needs to be examined further with a greater number of soils. In comparison, a poor relationship was found between the hot‐water extractable N (HWN) and loss of DON by leaching, despite HWN previously being shown to be a measure of the mineralizable pool of N in soils, possibly reflecting the greater competition for N than C in these soils.  相似文献   

2.
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   

3.
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   

4.
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   

5.
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   

6.
Dissolved organic matter (DOM) is a small but reactive pool of the soil organic matter (SOM) that contributes to soil dynamics including the intermediary pool spanning labile to resistant SOM fractions. The solubilization of SOM (DOM production) is commonly attributed to both microbially driven and physico-chemically mediated processes, yet the extent to which these processes control DOM production is highly debated. We conducted a series of experiments using 13C-ryegrass residue or its extract (13C-ryegrass-DOM) separately under sterile and non-sterile conditions to demonstrate the importance of DOM production from microbial and physico-chemical processes. Soils with similar properties but differing in parent material were used to test the influence of mineralogy on DOM production. To test the role of the source of C for DOM production, one set of soils was leached frequently with 13C-ryegrass-DOM and in the other set of soils 13C-ryegrass residue was incorporated at the beginning of the experiment into the soil and soils were leached frequently with 0.01 mol L−1 CaCl2 solution. Leaching events for both treatments occurred at 12-d intervals over a 90-day period. The amount of dissolved organic C and N (DOC and DON) leached from residue-amended soils were consistently more than 3 times higher in sterile than non-sterile soils, decreasing with the time. Despite changes in the concentration of DOC and DON and the production of CO2, the proportion of DOC derived from the 13C-ryegrass residue was largely constant during the experiment (regardless of microbial activity), with the majority (about 70%) of the DOM originating from native SOM. In 13C-residue-DOM treatments, after successive leaching events and regardless of the sterility conditions i) the native SOM consistently supplied at least 10% of the total leached DOM, and ii) the contribution of native SOM to DOM was 2–2.9 times greater in 13C-residue-DOM amended soils than control soils, suggesting the role of desorption and exchange reactions in DOM production in presence of fresh DOM input. The contribution of the native SOM to DOM resulted in higher aromaticity and humification index. Our results suggest that physico-chemical processes (e.g. exchange or dissolution reactions) can primarily control DOM production. However, microbial activity affects SOM solubilization indirectly through DOM turnover.  相似文献   

7.
We investigated the importance of physico‐chemical mechanisms responsible for the release of dissolved organic matter (DOM) from a peaty soil. Columns containing peat aggregates (embedded within a sand matrix) provided an experimental system in which both convective and diffusive processes contributed to DOM leaching. The use of aggregated peat avoided the problems associated with traditional batch equilibration experiments in which soil structure is destroyed. Biotic and abiotic processes operating in the columns were manipulated by working with two unsterilized columns (at 5°C and 22°C) and one gamma irradiation‐sterilized column (5°C). Continuous solute flows (< 80 hours) and periods of flow interruption (five interruptions of 6 hours to 384 hours) were applied to the columns (using a 1‐mm NaCl electrolyte) to investigate mechanisms of diffusion‐controlled release of DOM. For all columns, dissolved organic carbon and nitrogen (DOC and DON) effluent concentrations increased after resumption of flow and the maximum concentrations increased with increased flow‐interruption duration. Measurements of effluent UV absorbance (λ= 285 nm) showed that the DOM leached immediately after the flow interruptions contained fewer aromatic moieties of lower molecular weight than the DOM leached after periods of steady flow. The sterilized column had larger DOC and DON effluent concentration spikes than those from the unsterilized column at 5°C (38 mg C dm−3 and 6.5 mg N dm−3 versus 13 mg C dm−3 and 6.5 mg N dm−3 after the 384 hours flow interruption). This result suggested that the concentrations of DOM resulting from physico‐chemical release mechanisms (sterilized column) were attenuated by biological activity (unsterilized columns). Our results indicate that the peat’s microporous structure provides reservoirs of DOM that interact with solute in transport pores via abiotic, rate‐controlled mass transport. Hence, diffusion can influence the quantity and composition of DOM leached from peat in the field depending on intensity and duration of rainfall.  相似文献   

8.
Microbial decomposition of extracted and leached dissolved organic carbon (DOC) and nitrogen (DON) was demonstrated from three pasture soils in laboratory incubation studies. DOC concentration in water extracts ranged between 29 and 148 mg C L?1 and DON concentration ranged between 2 and 63 mg N L?1. Between 17 and 61 % of the DOC in the water extracts were respired as CO2 by microbes by day 36. DON concentrations in the extracts declined more rapidly than DOC. Within the first 21 days of incubation, the concentration of DON was near zero without any significant change in the concentration of NO3 ? or NH4 +, indicating that microbes had utilized the organic pool of N preferentially. Decomposition of leached DOC (ranged between 7 and 66 mg C L?1) and DON (ranged between 6 and 11 mg N L?1) collected from large lysimeters (with perennial pasture; 50 cm diameter?×?80 cm deep) followed a similar pattern to that observed with soil extracts. Approximately 28 to 61 % of the DOC in leachates were respired as CO2 by day 49. The concentration of DON in the leachates declined to below 1 mg N L?1 within 7–14 days of the incubation, consistent with the observations made with extractable DON. Our results clearly show that DOC and DON components of the dissolved organic matter in pasture soils, whether extracted or leached, are highly decomposable and bioavailable and will influence local ecosystem functions and nutrient balances in grazed pasture systems and receiving water bodies.  相似文献   

9.
Dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soils are increasingly recognized as important components of nutrient cycling and biological processes in soil‐plant ecosystems. The aims of this study were to: (i) quantify the pools of DON and DOC in a range of New Zealand pastoral soils; (ii) compare the effects of land use changes on these pools; and (iii) examine the seasonal variability associated with these two components of dissolved organic matter. Soil samples (0–7.5 cm depth) from 93 pastoral sites located in Northland, Waikato, Bay of Plenty and Otago/Southland, New Zealand, were collected in autumn. Adjacent sites under long‐term arable cropping or native vegetation and forestry land use were also sampled at the same time to estimate the impacts of different land use on DON and DOC in these soils. Twelve dairy and 12 sheep and or beef pastures were sampled in winter, spring, summer and autumn for a 2‐year period to study the seasonal fluctuations of DON and DOC. A field incubation study was also carried out in a grazed pasture to examine fluctuations in the concentrations of and and DON levels in soil. Other soil biological properties, such as microbial biomass‐C, biomass‐N and mineralizable N, were also measured. Pastoral soils contained the greatest amounts of DON (13–93 mg N kg−1 soil, equivalent to 8–55 kg N ha−1) and DOC (73–718 mg C kg−1 soil, equivalent to 44–431 kg C ha−1), followed by cropping and native vegetation and forestry soils. The DON concentration in soils was found to be more seasonally variable than DOC. There was approximately 80% fluctuation in the concentration of DON in winter from the annual mean concentration of DON, while DOC fluctuated between 23 and 28% at the dairy and the sheep and beef monitoring sites. Similar fluctuations in the concentrations of DON were also observed in the field incubation studies. These results indicate that DON is a dynamic pool of N in soils. There was a strong and significant positive correlation between DON and DOC in pastoral soils (r = 0.71, P < 0.01). There were also significant positive correlations between DON and total soil C (r = 0.59, P < 0.01), total soil N (r = 0.62, P < 0.01) and mineralizable N (r = 0.47, P < 0.01). The rather poor correlations between total soil C and N with DOC and DON, suggest other biogeochemical processes may be influencing concentrations of DOC and DON in these soils. Given the size of DON and DOC pools in the pastoral soils, we suggest that these pools of C and N should be taken into account when assessing the impact of pastoral land use on soil C and N enrichment of surface and groundwater.  相似文献   

10.
《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   

11.
Dissolved organic nitrogen (DON) represents a significant pool of soluble N in many soils and freshwaters. Further, the low molecular weight (LMW) component of DON represents an important source of N for microorganisms and can also be utilized directly by some plants. Our purpose was to determine which of the pathways in the decomposition and subsequent ammonification and nitrification of organic N represented a significant block in soil N supply in three agricultural grassland soils. The results indicate that the conversion of insoluble organic N to LMW-DON and not LMW-DON to NH4+ or NH4+ to NO3− represents a major constraint to N supply. We hypothesize that there are two distinct DON pools in soil. The first pool comprises mainly free amino acids and proteins and is turned over very rapidly by the microbial community, so it does not accumulate in soil. The second pool is a high molecular weight pool rich in humic substances, which turns over slowly and represents the major DON loss to freshwaters. The results also suggest that in NO3− rich soils the uptake of LMW-DON by soil microorganisms may primarily provide them with C to fuel respiration, rather than to satisfy their internal N demand.  相似文献   

12.
Dissolved organic carbon (DOC) and nitrogen (DON) have been hypothesized to play a central role in nutrient cycling in agricultural soils. The aim of this study was to investigate the annual dynamics of DOC and DON in a Greek vineyard soil and to assess the potential role of DON in supplying N to the vines. Our results indicated that significant quantities of DOC and DON existed in soil throughout the year and that peaks in concentration appeared to correlate with discrete agronomic events (e.g. onset of irrigation and plowing). Both field and laboratory experiments showed that free amino acids were rapidly mineralized in soil and that consequently free amino acids represented only a small proportion of the soil's total soluble N. Due to rapid nitrification the soil solution N was dominated by NO3−. Based upon the calculation of a plant-soil N budget and previous studies on N uptake in Vitis vinifera L., it is likely that DON uptake does not directly supply significant amounts of N to the plant. As the soil was not N limited we hypothesize that amino acids are used by the microbial community more as a source of C rather than a source of N. While we conclude that DON constitutes a significant N pool in vineyard soils further work is required to chemically characterize its constituent units and their relative bioavailability so that their overall role in N cycling can be determined.  相似文献   

13.
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   

14.
In forested ecosystems, the quality of dissolved organic matter (DOM) produced by freshly senesced litter may differ by litter type and species, and these differences may influence the amount of DOM that is respired versus that which may either contribute to soil organic matter accumulation or be leached from the ecosystem. In this study, we investigated the effect of litter type (including freshly senesced fine root, leaf, fine woody, and reproductive litter) and species (5 species of leaf litter) on several measures of the quality of DOM produced at a site along a primary successional chronosequence at Mt. Shasta, California. We measured differences in solid litter chemistry (C, N, and P concentration) and differences in the concentration of dissolved organic C, N, and P (DOC, DON, and DOP, respectively), water-soluble monomeric carbohydrates, polyphenols, proteins, fractions of DOC, as well as UV absorbance. For several aspects of DOC quality, DOM from fine roots was less labile than DOM from leaf litter. In contrast to DOC quality, soluble material originating from fine roots was high in labile forms of dissolved N and P in comparison to leaf litter. We also found that leaf litter with greater total %N or %P in solid litter had higher DON or DOP concentration (and higher total soluble P concentration). A very high percentage, on average 72% (up to 89%) of the total P in leaf litter was water-soluble and mostly inorganic P. Concentrations of soluble polyphenols were strongly related to DOC, and concentrations of soluble proteins were significantly related to DON in leaf litter of different species. During primary succession at the Mt. Shasta site, an increasing ratio of root to leaf litter production and shifting species composition has been found to occur, and the results of this study suggest that some aspects of DOC quality reflect a decrease in labile forms of DOC originating from both above and belowground litter. In contrast, dissolved N and P reflect an increase in labile forms with increasing inputs of root litter. In particular, our study has demonstrated important differences in the quality of inputs of DOM from freshly senesced root and leaf litter, and these differences have implications for C and nutrient cycling.  相似文献   

15.
Dissolved organic matter (DOM) plays an important role in transport, storage and cycling of carbon (C) and nitrogen (N) in forest soils where litter is one of the main sources. The aim was to study the amount and characteristics of DOM leached from freshly fallen litters of silver birch (Betula pendula Roth.), Norway spruce (Picea abies (L.) Karst.) and their mixture during decomposition. DOM was collected after irrigation on eight occasions during 252 days incubation in the laboratory at about 18°C, including one freeze‐thaw cycle. During the incubation about 33–35% of C from birch and spruce litter and 40% of C from their mixture was lost. The total cumulative flux of dissolved organic carbon (DOC) from the mixture of litters was approximately 40% larger than that from single litters. The flux of DOC, DON, phenolic compounds and proteins followed a two‐stage pattern during decomposition. In the first stage the initially large fluxes decreased gradually. In the second stage, after freezing and thawing, the fluxes tended to increase again. Mixing birch and spruce litters and a freeze‐thaw cycle seems to increase the decomposition of litter and result in the increased flux of DOC, DON and phenolic compounds. The flux of hemicelluloses and the degradability of DOM were large at the first leaching occasion and decreased during the incubation. Birch had a 40% larger total flux of easily degradable DOM than spruce, supporting the previous consistent signs of greater microbial biomass and activities related to C and N cycling in soil under birch than under spruce. It is known that recalcitrant DOM might be stabilized whereas labile DOM may promote microbial activity and nutrient cycling. We conclude that the storage and cycling of C and N is affected by both tree species and degradation stage of litter in forest soils.  相似文献   

16.
Abstract

Diethylaminoethyl cellulose (DEAE cellulose), a weak anion exchange resin, has been used to isolate dissolved organic matter (DOM) from soil solutions collected from three different soil types, to investigate the amount of DOM isolated from soil solutions of various origin, and the extent to which inorganic ions are isolated together with DOM. The concentration of DOM in the various soil solutions ranged from 2.5 to 32.8 mg#lbL‐1 DOC. More than 80% of dissolved organic carbon (DOC) was usually isolated with DEAE cellulose. High concentrations of aluminum (Al) and sulfate (SO4 2‐) in the soil solutions have reduced DOC recovery. More than 90% of potassium (K+), calcium (Ca2+), and magnesium (Mg2+), were removed during the isolation procedure, but 10 to 20% of Al and 30 to 40% of iron (Fe) were isolated together with the DOC, probably due to strong complexation to DOM. The advantages of using DEAE cellulose were that the use of strong acids and bases was limited and that pH adjustments of the sample, leading to chemical modification of DOM, was not required.  相似文献   

17.
Effects of (1) the addition of 35 kg N ha-1yr-1(as NH4NO3) and (2) interception of throughfall and litterfall by means of a roof on concentrations, chemical characteristics and dynamics of dissolved organic matter (DOM) in acid forest soils (podzols) were studied at Gårdsjön, Sweden. A non-manipulated catchment served as a reference. After 4 yr of treatment no significant effects of either manipulation were found on concentrations and characteristics of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON). The variability of these parameters within catchments appeared to be of the same order of magnitude as the variability between catchments. At all sites, DON contributed more than 70% of the total dissolved nitrogen. In general, the proportion of hydrophilic DOC increased with depth. In contrast, to other studies the C/N ratio of DOM at Gårdsjön did not show a clear pattern with depth. Other studies in SE U.S.A. have suggested that relatively low C/N ratios at depth are due to increased contribution of hydrophilic neutrals to DOC. However, this fraction appears to be small in temperate and boreal spruce forest soils, including Gårdsjön.  相似文献   

18.
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 CO2 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 CO2 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   

19.
There is now clear evidence for a prolonged increase in atmospheric CO2 concentrations and enrichment of the biosphere with N. Understanding the fate of C in the plant-soil system under different CO2 and N regimes is therefore of considerable importance in predicting the environmental effects of climate change and in predicting the sustainability of ecosystems. Swards of Lolium perenne were grown from seed in a Eutric Cambisol at either ambient (ca. 350 μmol mol−1) or elevated (700 μmol mol−1) atmospheric pCO2 and subjected to two inorganic N fertilizer regimes (no added N and 70 kg N ha−1 month−1). After germination, soil solution concentrations of dissolved organic C (DOC), dissolved inorganic N (DIN), dissolved organic N (DON), phenolics and H+ were measured at five depths down the soil profile over 3 months. The exploration of soil layers down the soil profile by roots caused transient increases in soil solution DOC, DON and phenolic concentrations, which then subsequently returned to lower quasi-stable concentrations. In general, the addition of N tended to increase DOC and DON concentrations while exposure to elevated pCO2 had the opposite effect. These treatment effects, however, gradually diminished over the duration of the experiment from the top of the soil profile downwards. The ambient pCO2 plus added N regime was the only treatment to maintain a notable difference in soil solution solute concentration, relative to other treatments. This effect on soil solution chemistry appeared to be largely indirect resulting from increased plant growth and a decrease in soil moisture content. Our results show that although plant growth responses to elevated pCO2 are critically dependent upon N availability, the organic chemistry of the soil solution is relatively insensitive to changes in plant growth once the plants have become established.  相似文献   

20.
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   

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