溶解性有机物（DOM)对农田土壤温室气体排放的影响及机制

Dissolved organic matter (DOM) is considered the most mobile and reactive component of the SOM pool depspite its occurrence in only small quantities in soils. As such, it regualtes major physical and biogeochemical processes in soils, can also play a vital role in the degradation of endogenous and exognous organic matter affeting C sequestration and N and P transformation and mobility in soil. Thus, DOM can mediated transformation of organic C into CO2 and CH4 as well as biological reduction of nitrates into N2 and N2O-greenhouse gases. In arable soils, crop residues provide the major source of DOM. The objective of this study will investigate the relationship between the emission of greenhouse gases and the dynamics of DOM under field condition, and quantification of crop residues-derived DOM conversion to CO2 and CH4, as well as nitrate reduction to N2O. Therefore, the batch incubation soil amended with 13C labelled crop residue and 15N labelled nitrate, pot experiment under wheat/corn growing amended with 13C labelled crop residue-derived DOM, and 15N labelled nitrate, and field plot trial under wheat/corn growing with crop residues retention will be carried out. The subsequent changes both in respired CO2, CH4 and N2O, DOC and DON, mirobial biomass-C and N, partical organic Cand N(POC and PON), NO3-N and NH4-N will be measured along in δ13C and δ15N values in the C/N pools. Moreover, tracing the fate fo crop residues-derived DOM in soil and its contribution to emission of greenhouse gases. The composition of DOM such as molecular structure, functional group content or size of molecular will be analysed by its specific UV absorbance and fluorescence spectroscopy. Meanwhile, nutrient availability, moisture and temperature along with the crop growth. Finally, to analyze the crucial intrinsic mechanism and the key external controlling factors, the factors affecting degradability of DOM and emission of greenhouse gases are grouped according intrinsic DOM characteristics and external soil properties, and the relationships between them are analyzed. The results will helpful for managing crop residues to eliminate the emission of greenhouse gases.

DOM是土壤微生物活动的能量和养分供应库，调节着土壤主要物理和生物化学过程，在碳氮磷转化迁移过程起着关键作用，与土壤温室气体产生排放直接关联。作物秸秆是农田土壤DOM的重要来源。所以，本项目目的为：研究秸秆来源DOM在土壤中的动态变化与行为归宿，及其对温室气体排放的影响与作用机制。为此，设置培养试验、盆栽试验和田间小区试验，培养试验添加13C标记粉碎秸秆和15N标记尿素，盆栽试验添加13C标记的秸秆DOM滤液和15N标记尿素，小区试验秸秆切碎直接还田。测定CO2、CH4和N2O，DOC和DON、POC和PON，微生物量C和N、NO3-N 和NH4-N动态分布及其13C和15N丰度，追踪外源DOM在土壤中的降解动态、转化分布与去向归宿。同时，利用光谱法分析DOM降解产物的分子结构、官能团含量等组分结构。最后结合土壤养分、水分、温度分析影响土壤温室气体产生排放规律及内在作用机制和外在影响因素。

作物秸秆是农田土壤中溶解性有机物（DOM ）的重要来源。DOM 是土壤中微生物活动的能量和养分供应库，调节着土壤主要理化和生物学过程，与土壤温室气体产生排放直接关联。为了探讨其作用过程与机制，通过室内培养、室外盆栽和田间小区试验，测定分析了玉米秸秆及其来源DOM对土壤温室气体排放的排放及其相关因素。主要创新结果如下：. (1)阐明了玉米秸秆及其来源DOM对土壤CO2和N2O排放的贡献——玉米秸秆及其来源DOM导致土壤CO2和N2O排放增加、减少土壤碳蓄积。室内培养试验表明：在无作物生长状况下，秸秆及其来源DOM对土壤累积CO2排放量的贡献率分别为34–40%和10–13%，秸秆来源DOM对土壤N2O排放的贡献率为68%；田间盆栽试验表明：在有作物生长条件下，秸秆来源DOM单独对土壤累积CO2排放的贡献率为55%，与N素共同作用对土壤累积CO2的排放的贡献率为46%；同时，秸秆及其来源DOM促进土壤N2O排放，占土壤累积排放量的32–46%。. (2)揭示了玉米秸秆及其来源DOM对土壤温室气体排放的激发效应及C、N耦合作用机理——秸秆及其来源DOM对土壤的激发效应及方向与其分解过程有关。盆栽试验表明：秸秆来源DOM主要产生正激发效应，促进土壤原有SOC分解增加达25%以上，与N素共同作用则高达45%以上。秸秆及其DOM添加促进土壤CO2和N2O的排放的作用机理为：秸秆主要与其提高了土壤DOC含量、qCO2、土壤蔗糖酶与β-葡萄糖苷酶活性有关，这四个指标可以解释变异的90%；而秸秆来源DOM主要是因为其提高了qCO2与土壤脲酶活性，二者可以解释其变异的83%。. (3)首次测定分析了秸秆还田土壤0–40cm土壤剖面分层温室气体通量及相关因素，结果表明由下向上土壤温室气体排放通量呈下降趋势，且秸秆还田与耕作措施具有明显的互作效应。. 研究结果为进一步深入研究秸秆还田固碳减排效应与机制、有效实施秸秆还田固碳减排措施提供了理论依据及技术支撑。