Litter type, but not plant cover, regulates initial litter decomposition and fungal community structure in a recolonising cutover peatland

Cutover peatlands are often rapidly colonised by pioneer plant species, which have the potential to affect key ecosystem processes such as carbon (C) turnover. The aim of this study was to investigate how plant cover and litter type affect fungal community structure and litter decomposition in a cutover peatland. Intact cores containing Eriophorum vaginatum, Eriophorum angustifolium, Calluna vulgaris and bare soil were removed and a mesh bag with litter from only one of each of these species or fragments of the moss Sphagnum auriculatum was added to each core in a factorial design. The presence or absence of live plants, regardless of the species, had no effect on mass loss, C, nitrogen (N) or phosphorus (P) concentrations of the litter following 12 months of incubation. However, there was a very strong effect of litter type on mass loss and concentrations of C, N and P between most combinations of litter. Similarly, plant species did not affect fungal community structure but litter type had a strong effect, with significant differences between most pairs of litter types. The data suggest that labile C inputs via rhizodeposition from a range of plant functional types that have colonised cutover bogs for 10-15 years have little direct effect on nutrient turnover from plant litter and in shaping litter fungal community structure. In contrast, the chemistry of the litter they produce has much stronger and varied effects on decomposition and fungal community composition. Thus it appears that there is distinct niche differentiation between the fungal communities involved in turnover of litter versus rhizodeposits in the early phases of plant succession on regenerating cutover peatlands.     

Contribution of dissolved organic matter to carbon storage in forest mineral soils

Dissolved organic matter (DOM) is often considered the most labile portion of organic matter in soil and to be negligible with respect to the accumulation of soil C. In this short review, we present recent evidence that this view is invalid. The stability of DOM from forest floor horizons, peats, and topsoils against microbial degradation increases with advanced decomposition of the parent organic matter (OM). Aromatic compounds, deriving from lignin, likely are the most stable components of DOM while plant‐derived carbohydrates seem easily degradable. Carbohydrates and N‐rich compounds of microbial origin produced during the degradation of DOM can be relatively stable. Such components contribute much to DOM in the mineral subsoil. Sorption of DOM to soil minerals and (co‐)precipitation with Al (and probably also with Fe), especially of the inherently stable aromatic moieties, result in distinct stabilization. In laboratory incubation experiments, the mean residence time of DOM from the Oa horizon of a Haplic Podzol increased from <30 y in solution to >90 y after sorption to a subsoil. We combined DOM fluxes and mineralization rate constants for DOM sorbed to minerals and a subsoil horizon, and (co‐)precipitated with Al to estimate the potential contribution of DOM to total C in the mineral soil of a Haplic Podzol in Germany. The contribution of roots to DOM was not considered because of lack of data. The DOM‐derived soil C ranges from 20 to 55 Mg ha^–1 in the mineral soil, which represents 19%–50% of the total soil C. The variation of the estimate reflects the variation in mineralization rate constants obtained for sorbed and (co‐)precipitated DOM. Nevertheless, the estimates indicate that DOM contributes significantly to the accumulation of stable OM in soil. A more precise estimation of DOM‐derived C in soils requires mineralization rate constants for DOM sorbed to all relevant minerals or (co‐)precipitated with Fe. Additionally, we need information on the contribution of sorption to distinct minerals as well as of (co‐)precipitation with Al and Fe to DOM retention.     

Contribution of plant root respiration to the CO2 emission from soil

The respiration activity of roots was studied in field experiments on gray forest and soddy-podzolic soils and under cropland and natural vegetation. It was shown that the contribution of roots to the CO₂ emission from the soil surface depends significantly on the method of determination. The contributions of fine and coarse roots to the total root respiration were approximately similar in forest ecosystems. The use of the method of substrate-induced respiration made it possible to obtain the best estimates of the contributions of root respiration and respiration of microorganisms. The application of glucose in the form of a dry mixture with sand or talc instead of in the water-soluble form appeared to be the optimal procedure for determining the root respiration under field moisture conditions.     

Molecular weight spectra of dissolved organic carbon in a rewetted Welsh peatland and possible implications for water quality

Abstract. Demand for water from catchments dominated by upland peat as a source of drinking water supplies in the UK is likely to increase in the future as demand per capita continues to rise (Thomsen 1990) and/or summer droughts increase in frequency (Arnell 1992). Concern has been expressed in recent years over rising colour levels (related to dissolved organic carbon (DOC) and iron (Fe)) from such catchments (e.g. Kay et al. 1989) causing reduced drinking water quality. One of the major causes of increased DOC concentrations is rewetting following periods of relative drought (Mitchell & McDonald 1992). Experimental rewetting of a naturally drained wetland in Mid‐Wales over four years was found to substantially increase the concentrations of DOC, and Fe in the pore‐water, with peak values of >60 mg dm^–3 (Fe) and >300 mg dm^–3 (DOC) after rewetting, compared with typical values of <1 mgdm^–3 (Fe) and <15 mg dm^–3 (DOC) under the drained conditions. Seasonal peak concentrations of Fe and DOC have since remained at these higher levels. Rewetting produced a selective enrichment of the >5000 to <90 000 apparent molecular weight (AMW) material and this fraction was found to yield peak Fe concentrations. Two additional peaks of DOC were also found in the experimental wetland (not present in the control wetland), of >90 000 to <200 000 AMW and >200 000 AMW material. The AMW spectrum of DOC in the experimental wetland changed with season, and the >90 000 to <200 000 AMW fraction could only be seen in spring, representing a transient pool of carbon that is rapidly transformed in or transported from the wetland. These findings suggest that rewetting of peatland following drought (e.g. due to climate change) has the potential to reduce water quality. Moreover, recent interest in restoration (rewetting) of drained peatlands (Wheeler & Shaw 1995) could create an additional source of DOC rich water.     

Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil

A significant proportion of the total nutrient in soil solution can be bound to organic molecules and these often constitute a major loss from soil to freshwater. Our purpose was to determine whether chemical extractants used for measuring inorganic N could also be used to quantify dissolved organic nitrogen (DON) and carbon (DOC) in soil. In a range of soils, DOC and DON were extracted with either distilled water or 2 M KCl and the amount recovered compared with that present in soil solution recovered by centrifugal-drainage. The recovery of DON and DOC from soil was highly dependent upon the method of extraction. Factors such as soil sampling strategy (number of samples over space and time), sample preparation (sieving and drying), soil storage, extraction temperature, shaking time, and soil-to-extractant volume ratio all significantly affected the amount of DOC and DON extracted from soil. To allow direct comparison between independent studies we therefore propose the introduction of a standardized extraction procedure: Replicate samples of unsieved, field-moist soil extracted as soon as possible after collection with distilled water, 0.5 M K₂SO₄ or 2 M KCl at a 1:5 w/v ratio for 1 h at 20 °C.     

Electron transfer capacity of soil dissolved organic matter and its potential impact on soil respiration

Purpose

Soil dissolved organic matter (DOM) as the labile fraction of soil organic carbon (SOC) is able to facilitate biogeochemical redox reactions effecting soil respiration and carbon sequestration. In this study, we took soil samples from 20 sites differing in land use (forest and agriculture) to investigate the electron transfer capacity of soil DOM and its potential relationship with soil respiration.

Materials and methods

DOM was extracted from 20 soil samples representing different land uses: forest (nos. 1–12) and agriculture (nos. 13–20) in Guangdong Province, China. Chronoamperometry was employed to quantify the electron transfer capacity (ETC) of the DOM, including electron acceptor capacity (EAC) and electron donor capacity (EDC), by applying fixed positive or negative potentials to a working electrode in a conventional three-electrode cell. The reversibility of electron accepting from or donating to DOM was measured by applying switchable potentials to the working electrode in the electrochemical system with the multiple-step potential technique. Carbon dioxide produced by soil respiration was measured with a gas chromatograph.

Results and discussion

Forest soil DOM samples showed higher ETC and electron reversible rate (ERR) than agricultural soil DOM samples, which may be indicative of higher humification rate and microbial activity in forest soils. The average soil respiration of forest soil (nos. 1–12) and agricultural soil (nos. 13–10) was 26.34 and 18.58 mg C g^?1 SOC, respectively. Both EDC and EAC of soil DOM had close relationship with soil respiration (p?<?0.01). The results implied that soil respiration might be accelerated by the electroactive moieties contained in soil DOM, which serve as electron shuttles and facilitate electron transfer reactions in soil respiration and SOC mineralization.

Conclusions

DOM of forest soils showed higher ETC and ERR than DOM of agricultural soils. As soil represents one of the largest reservoirs of organic carbon, soil respiration affects C cycle and subsequently CO₂ concentration in the atmosphere. As one of the important characteristics of soil DOM related to soil respiration, ETC has a significant impact on greenhouse gas emission and soil carbon sequestration but has not been paid attention to.     

Grassland plants affect dissolved organic carbon and nitrogen dynamics in soil

Dissolved organic carbon (DOC) and nitrogen (DON) are central in many nutrient cycles within soil and they play an important role in many pedogenic processes. Plants provide a primary input of DOC and DON into soil via root turnover and exudation. Under controlled conditions we investigated the influence of 11 grass species alongside an unplanted control on the amount and nature of DOC and DON in soil. Our results showed that while the presence of plants significantly increases the size of a number of dissolved nutrient pools in comparison to the unplanted soil (e.g. DOC, total phenolics in solution) it has little affect on other pools (e.g. free amino acids). Grass species, however, had little effect on the composition of the DOC, DON or inorganic N pools. While the concentration of free amino acids was the same in the planted and unplanted soil, the flux through this pool was significantly faster in the presence of plants. The presence of plants also affected the biodegradability of the DOC pool. We conclude that while the presence of plants significantly affects the quantity and cycling of DOC and DON in soil, comparatively, individual grass species exerts less influence.     

Leaching of dissolved organic carbon in soil following anhydrous ammonia application

The transport of anhydrous NH₃-solubilized soil organic matter from surface to subsurface soils may affect subsurface microbial activity. In the present study we determined the impact of anhydrous NH₃-N fertilizer on organic C solubilization and the propensity of solubilized C to leach with percolating water. In fertilized treatments, anhydrous NH₃ was subsurface-banded at 20g N m^-2 in ridge or valley areas of a ridge tillage system. In contol treatments, 0g N m^-2 was banded into the valley area of a ridge tillage system. Rainfall (17 cm) was applied with a drop-type artificial rainfall simulator 3, 10, and 24 days after the fertilizer application. The treatments were replicated twice. Grid lysimeters (15 by 15 cm) were placed 75 cm below the soil surface of a Brandt silty clay loam (fine-silty over sandy or sandy skeletal mixed Pachic Udic Haploboroll). Lysimeters were used to collect percolating water temporally and spatially. The application of N fertilizer increased dissolved organic C concentrations in percolating water when rainfall was applied 3 days after the fertilizer application. However, when the rainfall was applied 24 days after the fertilizer application the dissolved organic C concentrations in percolating water was not influenced by anhydrous NH₃ application. The smaller dissolved organic C concentrations in percolating water with a longer incubation time were most likely the result of microbial assimilation or respiration of solubilized C.     

中国西北棉花根系呼吸对土壤呼吸贡献率的研究

To measure the contribution of root respiration (Rr) to total soil respiration (Rt) in arid cotton fields, eighteen plots, nine for girdling and nine control, were built in an arid cotton field in the Aksu National Experimental Station of Oasis Farmland Ecosystem, Xinjiang of China. Given the difference of soil respiration between girdled plots and non-girdled control plots, the components of soil respiration, root respiration (Rr) and respiration originating from decomposition (Rd) were divided. The temperature sensitivities of R r and R d were analyzed, respectively. The results showed that the average contribution of R r to R t in arid cotton field was about 32% during the study period. The temperature-response curve of R r differed from that of Rd . The dynamic variation of R d was more related to the change of soil temperature as compared to Rr . Rr and Rd had different responses to the variation of environment, and thus new models capable of differentiating between Rr and Rd are needed for evaluating the different factors controlling these two components of soil respiration in arid cotton field.     

Effects of sulfate deposition on pore water dissolved organic carbon,nutrients, and microbial enzyme activities in a northern peatland

Export of dissolved organic carbon from lakes and streams has increased throughout Europe and North America over the past several decades. One possible cause is altered deposition chemistry; specifically, decreasing sulfate inputs leading to changes in ionic strength and dissolved organic carbon solubility. To further investigate the relationship between deposition chemistry and dissolved organic carbon export in peatlands, a field experiment was conducted to compare the pore water chemistry and peat microbial enzyme activity of mesocosms receiving sulfate amendments to mesocosms receiving no additions. To consider how peatlands respond during recovery from increased inputs of sulfate, samples were also analyzed from an area of the same peatland that was previously amended with sulfate. Current additions of sulfate decreased dissolved organic carbon concentration and increased dissolved organic carbon aromaticity. Total dissolved phosphorus decreased in response to current sulfate amendments but was elevated in the area of the peatland recovering from sulfate amendment. The total dissolved phosphorus increase, which was reflected in microbial enzyme activity, may have shifted the system from P limitation to N limitation. This shift could have important consequences for ecosystem processes related to plant and microbial communities. It also suggests that the recovery from previous sulfate amendments may take longer than may be expected.     

冀西北栗钙土有机碳、酶活性及土壤呼吸强度特征研究

土壤有机碳(质)水平的高低是评价土壤肥力高低的重要指标之一,如何提高土壤有机碳(质)研究一直是国内外土壤科学工作者关注的课题。近年来,随着全球环境变化对陆地生态系统的影响,土壤有机碳逐渐成为公众和科学界关注的热点[1]。研究陆地碳循环机制及其对全球变化的响应,是预测大气CO2含量及气候变化的重要基础,这已引起科学界的高度重视[2]。目前,有关土壤碳循环研究主要集中在大气CO2浓度升高对土壤酶活性、有机物料分解、土壤微生物、土壤有机质、腐殖质组成、农作物养分利用、植物生长、光合作用、根系生长及其分泌物等生理生态方面的影响[3～12],以及施肥对农田土壤碳循环、微生物及酶活性的影响[13～16],     

Direct effects of litter decomposition on soil dissolved organic carbon and nitrogen in a tropical rainforest

To clarify how litter decomposition processes affect soil dissolved organic carbon (DOC) and soil dissolved nitrogen (DN) dynamics, we conducted a field experiment on leaf litter and collected DOC and DN from the underlying soil in a tropical rainforest in Xishuangbanna, southwest China. Principal components analysis (PCA) showed the first PCA axis (corresponding to degraded litter quantity and quality) explained 61.3% and 71.2% of variation in DOC and DN concentrations, respectively. Stepwise linear regression analysis indicated that litter carbon mass controlled DOC and hemicellulose mass controlled DN concentrations. Litter decomposition was the predominant factor controlling surface-soil DOC and DN dynamics in this tropical rainforest.     

Contribution of crop residue carbon to soil respiration at a northern Prairie site using stable isotope flux measurements

Heterotrophic respiration from agricultural soils can be differentiated as originating from microbial decomposition of recent litter inputs or crop residue carbon (CRC) and resident soil organic carbon (SOC) pools of varying age and stages of decomposition. Our objective was to determine the relative contributions of these pools to respiration in a northern agroecosystem where the non-growing season is long. A tunable diode laser trace gas analyzer was used to determine atmospheric stable C isotope ratio (δ¹³C) values and ¹²CO₂ and ¹³CO₂ fluxes over an agricultural field in the Red River Valley of southern Manitoba, Canada. Measurement campaigns were conducted in the fall of 2006 and spring of 2007 following harvest of a maize (C₄) crop from soil having SOC derived from previous C₃ crops. Stable CO₂ isotopologue gradients were measured from the center of four 200 × 200 m experimental plots, and fluxes were calculated using the aerodynamic flux gradient method. The soil in two of the experimental plots underwent intensive tillage, while the other two plots were managed using a form of reduced tillage. Approximately 70% and 20-30% of the total respiration flux originated from the maize C₄-CRC during the fall of 2006 and spring of 2007, respectively. At least 25% of the maize residue was lost to respiration during this non-growing period. No difference in the partitioning of heterotrophic respiration into that derived from CRC and SOC was detected between the intensive tillage and recently established reduced tillage treatments at the site.     

Poorly crystalline iron and aluminium oxides contribute to the carbon saturation and sorption of dissolved organic carbon in the soil

Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg^?1). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.     

Salinity and sodicity affect soil respiration and dissolved organic matter dynamics differentially in soils varying in texture

The individual effects of salinity and sodicity on organic matter dynamics are well known but less is known about their interactive effects. We conducted a laboratory incubation experiment to assess soil respiration and dissolved organic matter (DOM) dynamics in response to salinity and sodicity in two soils of different texture. Two non-saline non-sodic soils (a sand and a sandy clay loam) were leached 3–4 times with solutions containing different concentrations of NaCl and CaCl₂ to reach almost identical electrical conductivity (EC_1:5) in both soils (EC_1:5 0.5, 1.3, 2.5 and 4.0 dS m^?1 in the sand and EC_1:5 0.7, 1.4, 2.5 and 4.0 dS m^?1 in the sandy clay loam) combined with two sodium absorption ratios: SAR < 3 and 20. Finely ground wheat straw residue was added (20 g kg^?1) as substrate to stimulate microbial activity. Cumulative respiration was more strongly affected by EC than by SAR. It decreased by 8% at EC 1.3 and by 60% at EC 4.0 in the sand, whereas EC had no effect on respiration in the sandy clay loam. The apparent differential sensitivity to EC in the two soils can be explained by their different water content and therefore, different osmotic potential at the same EC. At almost similar osmotic potential: ?2.92 MPa in sand (at EC 1.3) and ?2.76 MPa in the sandy clay loam (at EC 4.0) the relative decrease in respiration was similar (8–9%). Sodicity had little effect on cumulative respiration in the soils, but DOC, DON and specific ultra-violet absorbance (SUVA) were significantly higher at SAR 20 than at SAR < 3 in combination with low EC in both soils (EC 0.5 in the sand and EC 0.7 and 1.4 in the sandy clay loam). Therefore, high SAR in combination with low EC is likely to increase the risk of DOC and DON leaching in the salt-affected soils, which may lead to further soil degradation.     

Release of dissolved organic carbon and nitrogen from forest floors in relation to solid phase properties,respiration and N-mineralization

Dissolved organic carbon (DOC) and nitrogen (DON) are important components of the carbon and nitrogen turnover in soils. Little is known about the controls on the release of DOC and DON from forest floors, especially about the influence of solid phase properties. We investigated the spatial variation of the release of DOC and DON from Oe and Oa forest floor samples at a regional scale. Samples were taken from 12 different Norway spruce sites with varying solid phase properties, including C/N ratio, pH, different fractions of extractable carbon and exchangeable cations. Most of these solid phase properties are available for large forested areas of Europe in high spatial resolution. The samples were incubated at water holding capacity for eight weeks at 15°C and then extracted with an artificial throughfall solution to measure DOC and DON release. The rates of soil respiration and N-mineralization were determined to estimate soil microbial activity. The release of DOC and DON from Oe samples was two- to threefold higher than from Oa samples. The amounts released differed by one order of magnitude among the sites. The DOC/DON ratios in the percolates of the Oa samples were much higher as compared to the solid phase C/N, indicating different release rates of DOC and DON. In contrast, the DOC/DON ratios of the Oe percolates were in the range of the C/N ratios of the solid phase. The release of DOC and DON from Oe samples was not statistically correlated to any of the measured solid phase parameters, but to N-mineralization. The DOC and DON release from the Oa samples was positively related only to pH and soil respiration. Overall it was not possible to explain the large spatial variation of DOC and DON release by the measured solid phase properties with satisfying accuracy.     

Mineralization of dissolved organic carbon in mineral soil solution of two forest soils

Dissolved organic carbon (DOC) constitutes an important carbon input flux to forested mineral soils. Seepage from mineral subsoils contains only small amounts of DOC because of mineralization, sorption or the formation of particulate organic matter (POM). However, the relation between these processes is largely unknown. Therefore, the objective of this study was to quantify the mineralization of DOC from different depths of forest soils, and to determine degradation rate constants for rapidly and slowly degradable DOC pools. Mineralization of DOC and formation of POM in mineral soil solution from two forested sites in northern Bavaria (Germany) were quantified in a 97 days laboratory incubation experiment. Furthermore, spectroscopic properties such as specific UV absorption and a humification index derived from fluorescence emission spectrometry were measured before and after incubation. DOC in all samples turned out to belong mainly to the stable DOC pool (> 95 %) with half‐lives ranging from years to decades. Spectroscopic properties were not suitable to predict the mineralization of DOC from mineral soils. However, together with data on DOC from the forest floor and long‐term data on DOC concentrations in the field they helped to identify the processes involved in C sequestration in mineral subsoils. Mineralization, formation of POM, and probably sorption seem all to be responsible for maintaining low concentrations of DOC in the upper mineral soil. DOC below the upper mineral soil is highly resistant to mineralization, and thus the further decrease of DOC concentrations in the subsoil as observed under field conditions cannot be attributed to mineralization. Our results suggest that sorption and to some minor extent the formation of POM may be responsible for C sequestration in the subsoil.     

Effect of forage crop establishment on dissolved organic carbon dynamics and leaching in a hill country soil

Intensive agricultural activities could affect the dynamics and leaching of dissolved organic carbon (DOC) and nitrate from agricultural soils to receiving waters. This study investigated soil DOC dynamics immediately (0–12 days) after spraying a hill country perennial pasture with agrochemicals to establish a winter forage crop for supplementary feed production. Two treatments were examined—perennial pasture (without agrochemicals) and swede (Brassica napobrassica Mill.) cropping (after spraying with agrochemicals), both growing on a Typic Eutrudept. Soil samples were collected from various depths down to 1 m, before the application of agrochemicals (day 0) and 1, 6 and 12 days thereafter. Dissolved organic carbon concentration below the surface soil (<5 cm) was generally not altered by the agrochemicals. This was further proved by the isotopic monitoring of DOC leaching on this soil. Conversely, the agrochemicals significantly (p = 0.03) increased DOC concentration within the 0–5‐cm soil depth on day 1, due to the direct contribution of organic molecules and/or displacement of organic compounds at adsorption sites by the agrochemicals; and on day 6, due to root necromass decomposition. The increase of nitrate in soil solution at this depth (0–5 cm) on days 6 and 12 suggests that the agrochemicals may have also enhanced nitrogen (N) mineralization in the surface soil. However, the significantly (p = 0.04) higher DOC/nitrate (molar ratio) of the agrochemical treatment suggests that the agrochemicals used for clearing out pasture before forage crop establishment could lead to a short‐term increase in surface soil denitrification.     

水稻品种和砷污染对土壤溶解性有机碳氮的影响

选取有机质含量和pH不同的2种水稻土(黄泥田和红泥田),通过盆栽实验研究砷(As)污染条件下,种植9个水稻品种对土壤溶解性有机碳(DOC)和溶解性有机氮(DON)含量的影响,分析水稻品种、As污染和土壤类型的相对影响与交互作用.结果表明,水稻品种显著影响了土壤DOC和DON的变化,在水稻收获后,DOC平均含量的大小顺序为杂交稻(41.09±0.92 mg kg-1)＞籼稻(38.10±1.53 mg kg-1)＞粳稻(37.74± 1.37 mg kg-1);DON平均含量的大小顺序为粳稻(2.94± 0.40 mg kg-1)＞杂交稻(2.61±0.42 mg kg-1)＞籼稻(1.45± 0.17 mg kg-1).As污染降低了土壤DOC和DON的含量,但不同品种水稻的响应不同.与对照相比,As污染条件下,黄泥田和红泥田中DOC平均含量分别下降了14.4％和11.1％,DON平均含量分别下降了65.0％和44.7％;DOC在种植杂交稻后降幅最小,而DON在种植籼稻后降幅最小.在两种水稻土中,黄泥田的DOC和DON平均含量高于红泥田,在没有As污染条件下,分别高22.4％和45.8％,这与黄泥田有机质含量和pH高有关.水稻品种、As污染和土壤类型对DOC和DON变化的影响不同,3个因子对DOC变化的相对贡献率分别为7.7％、15.5％和27.6％,对DON变化的相对贡献率分别为14.7％、24.2％和2.0％.     

不同培肥处理对土壤溶解性有机碳含量及特性的影响

以黄土高原南部地区的长期肥料定位试验为研究对象,通过室内测定及培养试验研究了不施肥(CK)、撂荒(FA)、施氮磷钾肥(NPK)、氮磷钾配施有机肥(MNPK)和氮磷钾配施秸秆(SNPK)培肥处理土壤中溶解性有机碳(DOC)的含量、结构特性及其降解特性。结果表明,在0～20 cm耕层土壤中,不同培肥处理土壤中DOC的含量变化范围在4.65～8.94 mg kg-1之间,平均为6.42 mg kg-1,各培肥处理间差异明显,其大小顺序为MNPKSNPKNPKFACK。由DOC溶液的UV280吸收值和腐殖化指数(HIXem)可以得出,不同培肥处理土壤中溶解性有机物中结构相对复杂的芳香化合物所占的比例明显不同,其大小顺序为SNPKMNPKFANPKCK。经过7d的生物降解培养,不同培肥处理土壤DOC溶液的降解率变化范围在19.3%～48.5%之间,平均为28.6%,其大小顺序为CKFANPKSNPKMNPK。随着培养的进行,DOC溶液中结构较为复杂的溶解性有机物的比例上升。