旱作农田土壤有机碳组分对秸秆碳投入的生物学响应机制

Soil organic carbon (SOC) is the core material of soil nutrient cycling and fertility. The conversion and accumulation of carbon fractions is one of the key factors that affect SOC sequestration, its content, stability and the relationship with soil microbial were crucial for revealing the SOC sequestration mechanism after different amount exogenous carbon into soil. This study took a farmland soil that was straw incorporated in 10 consecutive years (2008-2018) on the Loess Plateau as the research object. Through defining soil C fractions in different amount of straw incorporation treatments. The objectives of the study were to: study the organic carbon distribution between different fractions and the release characteristics of CO2 in the process of the mineralization; clarify the evolution and the stability characteristics of soil carbon fraction under different straw incorporation amount treatments; combine with different carbon source culture to clear the microorganism diversity and selectivity of carbon usage under different amounts of straw carbon input; explore the response to microbial communities and carbon components to reveal the biological response mechanism of different amount straw carbon inputs on the changes of SOC components. So as provide a new basis to further study on SOC pool stability and soil carbon sequestration mechanism under straw incorporation on rainfed farmland in this area.

土壤有机碳是土壤养分循环及肥力供应的核心物质，其碳组分的转化和积累是影响农田土壤有机碳固持关键因素之一，其含量与稳定性同土壤微生物之间的相互关系对于揭示不同量外源碳投入后的土壤固碳机理至关重要。本研究拟以黄土高原连续10年（2008-2018）不同秸秆还田量农田土壤为研究对象，通过对不同还田量处理土壤进行物理分组，研究有机碳在不同组分间的分配以及矿化过程中CO2的释放特征，阐明土壤物理碳组分演变规律及稳定性特征；分析不同量秸秆碳投入后土壤微生物特性变化，结合不同组分碳源培养试验，明确微生物在不同量秸秆碳投入后对碳源利用的差异性和选择性，探讨微生物群落与碳组分之间的响应关系，揭示不同量秸秆碳投入对土壤有机碳组分变化的生物学响应机制。项目预期成果对深入认识旱作农田长期秸秆还田后土壤固碳过程及碳库稳定性机理具有重要意义。

本项目针对西北旱作覆膜农田土壤质量下降问题，研究不同量秸秆还田后覆膜农田土壤有机碳含量、组分碳、酶活性以及作物产量变化，综合评价不同秸秆还田量对旱作覆膜农田土壤固碳培肥增产机理，为北方旱作覆膜农田绿色可持续发展提供一定的参考依据。获得如下主要结果：（1）秸秆还田后可显著提高覆膜农田0-60 cm土层土壤>0.25 mm团聚体含量，且随还田量的增加而增大，BH、BM、BL较BN处理机械稳定性团聚体平均分别提高45.20%（P<0.05）、19.30%（P<0.05）和7.55%。团聚体稳定性（MWD）也随秸秆还田量的增加而增大，且覆膜处理效果优于不覆膜处理；（2）在同一秸秆还田量下，各覆膜处理0-60 cm土壤有机碳均低于对应不覆膜处理，且随着还田年限的增加降幅逐渐降低。在相同种植模式下，各秸秆还田处理土壤有机碳、颗粒有机碳、可溶性有机碳和微生物量碳含量均随秸秆还田量的增加逐渐增大，且增幅有所提高；（3）秸秆还田可以改善土壤物理环境，从而提高耕层0-60 cm土壤蔗糖酶和β-葡萄糖苷酶活性，且覆膜处理增幅效果优于不覆膜处理，尤其是高量秸秆还田处理（BH）；土壤过氧化氢酶和蔗糖酶对土壤有机碳和团聚体有机碳正相关，而土壤β葡萄糖苷酶与SOC显著正相关（P<0.05），与土壤粒级有机碳极显著正相关（P<0.01）；（4）在各年份覆膜处理均可显著提高玉米株高和干物质积累；在相同种植方式下，秸秆还田量对玉米株高无明显影响，但可显著提高收获期干物质积累量，且增加幅度会随着降水量的增多显著提高；（5）在相同种植模式下随秸秆投入量的增加玉米产量逐渐增大，且覆膜处理的产量均高于不覆膜处理，增幅18.7%—41.8%，玉米产量与土壤 β-葡萄糖苷酶、蔗糖酶和过氧化物酶活性之间呈显著正相关，随有机碳含量升高，玉米产量逐渐提高，但其增长趋势逐渐平缓。总体来看，秸秆还田可通过影响土壤碳转化的各个因素（如土壤团聚体粒级分布、结构稳定性、土壤酶活性）促进土壤有机碳及其活性组分的积累，进而提升旱作农田土壤肥力并增加作物产量，且在高量还田下增幅较好。