冻融对土壤氮素转化和N2O排放的影响研究进展

在中、高纬度及高海拔地区，土壤冻融现象常有发生。冻融作用通过影响土壤理化性质和生物学性状进而影响土壤氮素转化过程及N₂O的产生和释放，但迄今关于冻融对土壤氮素转化过程影响的研究结果还不尽一致，正效应或负效应均存在，土壤冻融期间N₂O排放对全年N₂O排放总量的贡献程度也存在着较大差异。本文重点论述了土壤冻结或冻融循环过程对土壤氮矿化、固持、硝化和反硝化等主要氮素转化过程的影响机制，同时分析了可引起冻融期间N₂O排放强度变化的四种可能机理（禁锢-释放、环境-底物诱导、N₂O还原酶抑制和化学反硝化增强）。指出在全球变暖背景下研究土壤冻融格局改变影响土壤氮素转化过程及N₂O排放的必要性，并简要提出了若干理论问题及研究方向。

Effects of freeze-thaw on soil nitrogen transformation and N2O emission: A review

As a natural phenomenon, soil freeze-thaw processes often occur in the regions of mid- and high latitudes and high altitude. Freeze-thaw can alter the soil physicochemical and biological properties, which thereby results in changes in soil nitrogen transformation and N₂O production and hence emission. Up to now, the impacts of freeze-thaw processes on soil nitrogen transformation found in previous studies remain inconsistent and large discrepancies have been found in the data on the contributions of N₂O losses during freeze-thaw period to annual emissions. In addition, this review also addresses the effects of freezing or a freeze-thaw cycle on major soil nitrogen transformation processes, including mineralization, immobilization, nitrification and denitrification, and possible explanations are discussed. Meanwhile, four potential mechanisms relating to N₂O emission intensity during the freeze-thaw period, such as N₂O trapped in and below the frozen layer and released from thawed soil, N₂O induced by circumstance and substrates, N₂O inhibited by N₂O reductase and N₂O enhanced by chemodenitrification, are systematically analyzed. The implications of global warming for soil freeze-thaw patterns are addressed, as well as the need to investigate alteration of soil nitrogen transformation and N₂O emission as affected by these circumstances. At last, some theoretical problems and perspectives of the study are brought forward.