秸秆还田条件下农田系统碳循环研究进展

秸秆还田是农田生态系统的固碳减排的一种措施，现已成为国内外学者研究的热点。本文在分析农田系统碳循环流通的基础上，将系统划分为土壤、植物和大气3个子系统，对秸秆还田条件下各个子系统中碳的流动变化情况进行讨论。在土壤子系统中，秸秆还田对土壤有机碳（SOC）、土壤矿化碳、土壤微生物碳（MBC）的变化都有作用。秸秆还田的初期可能会降低微生物利用碳源的能力，影响群落物种分布的均匀度，致使作物对碳、氮利用率下降；然而，长期的效应仍会增加土壤微生物的多样性和活性。研究亦认为秸秆还田特别是与有机肥配合使用，能够提高土壤有机碳的含量；对土壤有机碳矿化具有明显促进作用，但是对土壤原有的有机碳矿化影响尚不清楚。秸秆还田在植物子系统中的影响主要集中在植物光合碳变化。已有的研究表明秸秆还田对作物光合作用的影响表现为正效应；然而根际碳流通的变化尚不清楚。在大气子系统中，秸秆还田能够增强旱地耕作土壤的呼吸作用，促进CO2的排放；而淹水条件下，秸秆还田使土壤有机碳矿化受到了明显抑制，对CO2没有明显影响。与此类似，淹水条件促进CH4排放，排水良好可以减少CH4的释放。事实上对CH4的排放而言，水份的影响可能比秸秆还田所产生的影响更大。笔者认为秸秆还田后土壤有机碳流通变化机理，及根际碳的流通变化影响仍有待进一步解析。其次，农业机械使用所产生的 CO2气体在研究秸秆还田模式时也应被考虑在内。除此之外，秸秆还田这种减排措施（CO2）的减排潜力、适宜应用的区域、可能的协同作用和一些限制及不利因素还没有得到确切的评估，实施过程中应考虑社会和经济层面上的因素。

Effect of returning straw on soil carbon cycle in cropland ecosystem

Straw returning is considered to be one of the most promising measures for carbon sequestration in China＆#39;s cropland ecosystem. The carbon balance can be analytically within three sub-systems, e.g. soil, crop and atmosphere. The changes of soil organic carbon （SOC）, mineralization of soil carbon, soil microbial biomass carbon （MBC） are mainly evaluated at the soil subsystem. Returning straw could reduce the ability of microbe utilizing carbon source, destroy species evenness, and finally decrease carbon and nitrogen utilization in soil, especially at the early stage of decomposition. However, returning straw could increase soil microbial diversity and activity at the end. Many field experiments have been demonstrated that returning straw increase the content of SOC, particularly with the organic fertilizer. Meanwhile, the mineralization of SOC was stimulated after returning straw, though it is still unclear that the kinetics of soil original carbon. In the crop subsystem, some experiments confirmed that positive contributions on crop photosynthesis and productivity, but the carbon circulation in rhizosphere are still mysterious after straw returning. In the atmospheric subsystem, the fortification of carbon dioxide （CO2） emissions in the non-irrigated cropland as a result of soil respiration are expected after returning straw, on the other hand, no clear patterns of CO2 emissions for paddy and irrigated soil were observed due to the inhabitation of SOC mineralization, mainly with the N fertilization. In fact, the emission of methane （CH4） in the waterlogging soil can be much reduced by a water draining process with the straw returning. The authors believed that returning straw is one of carbon sequestrations for agronomy, more factors should be further considered. In the research, the kinetics of soil organic carbon is still the key for carbon sequestration, particularly carbon circulation of SOC and rhizosphere. The CO2 emission from fossil fuel using of agricultural machinery in the returning straw should be account in agronomy system. For the agronomy operation, the factors of implementation should be assessed for the time, soil and crop rotation and other related agronomy factors, e.g. fertilizer, as well as the factors of social and economic.