东北农田黑土N2O排放研究进展

农田是温室气体氧化亚氮（N2O）的重要排放源，位于东北地区的黑土地是我国重要的粮食生产基地。目前我国农田N2O排放增速正在放缓，但是东北黑土区仍在加快。针对我国东北黑土区的自身特点和N2O排放研究现状，本文综合分析了黑土N2O排放特征、产生过程与影响因素。结果表明，东北农田黑土N2O-N背景排放量平均为0.56±0.29 kg·hm?2，施用化肥黑土N2O-N平均排放量为1.49±1.09 kg·hm?2，化肥氮诱导的N2O排放系数（EF）为0.45%±0.42%。与中国旱地和世界其他黑土区相比，东北农田黑土的背景排放量和EF均处于较低水平。这是因为在正常降雨条件下，东北黑土N2O主要是由硝化作用产生，反硝化作用受到活性碳缺乏的限制。冻融过程则可能促进反硝化作用进行，诱导春融期N2O出现爆发式排放。与我国其他农田相比，东北黑土N2O排放研究明显不足，今后应加强对不同区域黑土N2O排放的原位观测，阐明冻融过程N2O的产生机制，评估黑土N2O排放对气候变化的响应；同时应加强研究秸秆还田、有机肥施用等措施对N2O排放的影响效应，从而制定出黑土地质量提升和N2O减排的双赢措施。

N2O Emissions from Black Soils in Northeast China

Cropland is an important source of the potent greenhouse gas nitrous oxide (N2O). The cultivated black soils located in Northeast China play a vital role in national grain production. It has been demonstrated that the growth rate of N2O emissions from Chinese croplands is slowing down but still accelerating in the black soil area of Northeast China. Aiming at comprehensively assessing N2O emissions and understanding the production mechanisms, in this study, we summarized and characterized the N2O emission intensity, production processes and influencing factors from the black soils in Northeast China. The results showed that the average N2O-N emissions from unfertilized and inorganic-fertilizer applied black soils were 0.56±0.29 and 1.49±1.09 kg·hm?2, respectively. The inorganic fertilizer-N induced N2O emission factor (EF) was 0.45%±0.42% on average across the black soils in Northeast China. Both the background emissions and the EF values were generally lower compared with those of other uplands in China and black soils in other countries. This was likely due to the limitation of denitrification by labile carbon under normal rainfall conditions, and thus the N2O emissions were predominately derived from nitrification. It was found that the freeze-thaw cycles could greatly promote denitrification and result in large pulses of N2O fluxes during spring thaw, which might dominate the annual emissions. Compared with croplands in other regions of China, studies on the N2O emissions from black soils in Northeast China are largely limited. In future research, the in-situ observations of N2O emissions from black soils in different regions of Northeast China should be strengthened, and the mechanisms involved in freeze-thaw induced N2O emissions should be clarified. This will facilitate the evaluation of the response of N2O emissions from black soils to global climate change. Also, there is a need to strengthen researches on the effects of crop residue returning, manure application, etc. on N2O emissions, to facilitate the development of win-win strategies for enhancing soil quality and simultaneously reduce N2O emissions from black soils.