生物炭对黄土高原碱性土壤N2O排放的影响及微生物学机制

Nitrous oxide (N2O) is a potent greenhouse gas, and agriculture is the main source of the global anthropogenic N2O emissions. Biochar with the carbon sequestration function has been widely used in agriculture. However, whether biochar incorporation into farmland soil could suppress N2O emissions is becoming a hot spot currently, and the potential microbial mechanisms are also not clear. Moreover, the present studies about this issue have given priority to the acidic soil. We hypothesized that the effectiveness of using biochar for reducing N2O emissions from the Loess Plateau alkaline agricultural soil is linked to its dominant N2O-formation pathway. When nitrification was the main process of N2O formation, biochar application would increase N2O emissions; while when denitrification was the main process of N2O formation, biochar application would decrease N2O emissions. In order to verify the above hypothesis, we will carry out the indoor culture experiments and the field experiments to explore the effects of wheat-straw biochar addition on N2O emissions from the wheatland soil of the Loess Plateau, determine whether the promotive or inhibitive effect is related to the main N2O-formation pathway, and distinguish the potential microbiological mechanisms controlling N2O emissions with biochar addition in alkaline soil. The study will be meaningful for clarifying the mechanisms of N2O emissions from alkaline farmland soil with biochar addition, and will provide a theoretical basis for the agricultural application of biochar in semi-arid region of the Loess Plateau.

氧化亚氮（N2O）是一种强效温室气体，农业活动是全球N2O排放的重要来源。生物炭作为农业固碳减排的有效措施被广泛应用，施加生物炭是否对土壤N2O排放有抑制作用成为当前研究的热点，相关微生物机理亦不清楚，且目前研究多针对酸性土壤。在黄土高原碱性农田土壤中，申请者提出生物炭对N2O排放的影响与N2O的产生途径有关。当硝化作用为N2O的主要产生途径时，生物炭对N2O排放有促进作用；当反硝化作用为N2O的主要产生途径时，生物炭对N2O排放有抑制作用。为证实以上假说，拟采用室内与野外实验相结合的方法，以秸秆生物炭为例，探究生物炭对黄土高原小麦田土壤N2O排放的影响、生物炭促进或抑制N2O排放是否与N2O的主要产生途径有关、生物炭对N2O排放的影响与相关微生物群落之间的响应关系。本研究对阐明施加生物炭条件下，碱性农田土壤N2O排放机制有重要意义，可为生物炭在黄土高原半干旱区的农业工程应用提供理论依据。

氧化亚氮（N2O）是一种强效温室气体，农业活动是全球N2O排放的重要来源。生物炭作为农业固碳减排的有效措施被广泛应用，施加生物炭是否对土壤N2O排放有抑制作用成为当前研究的热点。本项目首先开展了玉米秸秆生物炭对碱性农田土壤N2O排放的影响研究。结果表明，无论在有利于硝化作用或反硝化作用的条件下，玉米秸秆生物炭均抑制了碱性农田土壤的N2O排放，且在反硝化作用条件下的抑制效果更明显。上述结论与本项目生物炭对农田土壤N2O排放的影响与N2O的主要产生途径有关的科学假说完全相反。因此，为验证此实验现象的广泛性，进一步研究了稻壳生物炭对酸性农田土壤N2O排放的影响，并深入探讨了相关机理。结果表明，在有利于硝化作用的条件下，与对照相比，添加2%、5%和10%（质量比）稻壳生物炭处理的N2O累积排放量分别减少了87.7%、94.6%和96.9%；在有利于反硝化作用的条件下，与对照相比，添加2%、5%和10%（质量比）稻壳生物炭处理的N2O累积排放量分别减少了59.4%、95.8%和99.97%。在反硝化作用条件下，稻壳生物炭抑制酸性农田土壤N2O排放的原因并非由于稻壳生物炭促进反硝化过程产生的N2O进一步还原为N2，或稻壳生物炭对NO3-和葡萄糖的强烈吸附作用导致反硝化底物的微生物可利用性降低，进而减少N2O排放；其原因可能为稻壳生物炭促进酸性农田土壤的有机碳矿化，导致反硝化过程碳源不足，从而抑制NO3-向N2O转化。另外，在硝化作用条件下，采用室内静态土壤培养实验（85天），研究了生物炭对农田土壤氨氧化细菌（AOB）数量和氨氧化速率动态变化的影响。结果表明，玉米秸秆生物炭显著促进了碱性农田土壤的氨氧化作用。因此，我们推测在硝化作用条件下，生物炭抑制农田土壤N2O排放的原因可能为生物炭促进了土壤的氨氧化作用，使NH4+易于转化为NO2-，避免氨氧化过程中间产物NH2OH向N2O的转化，进而抑制N2O排放。本研究对阐明施加生物炭条件下农田土壤N2O排放机制有重要意义，可为生物炭的农业工程应用提供理论依据。