亚热带典型森林土壤NO与N2O排放及其对氮沉降响应的微生物机制

Forest soils are an important source of nitric oxide (NO) and nitrous oxide (N2O). Recently, an increasing nitrogen deposition may have altered the fluxes of NO and N2O. Previous studies, however, have focused little on soil NO emission and its response to nitrogen deposition. Furthermore, the contributions of nitrification and denitrification to NO and N2O emissions, and the associated microbial mechanisms in response to nitrogen deposition remain unclear. Therefore, this project will use the simultaneous monitoring technique in situ and the 15N isotopic labeling technique in laboratory to investigate the seasonal variations of NO and N2O emissions from forest soils (i.e., evergreen broadleaf forest, conifer and broadleaf mixed forest and pine forest) and their responses to N deposition along an altitude gradient in the Wuyi Mountains. The project will also determine the contributions of nitrification and denitrification to NO and N2O emissions and their relationships with the abundance of nitrification and denitrification functional genes. The implementation of this project will shed light into NO and N2O emissions from subtropical forest soils and reveal the microbial mechanisms involved in the production of soil NO and N2O. It will also provide the theoretical basis for the evaluating and predicting of NO and N2O emissions and their responses to N deposition in this region.

森林土壤是一氧化氮(NO)与氧化亚氮(N2O)的重要来源。近年来，氮沉降量的持续增加可能改变森林土壤NO与N2O的排放通量。然而，目前关于森林土壤NO排放及其对氮沉降响应的研究很少，且有关森林土壤硝化和反硝化作用对NO与N2O排放的贡献及其对氮沉降响应的微生物机制仍不清楚。因此，本项目拟以武夷山不同海拔高度森林(常绿阔叶林、针阔混交林和针叶林)为研究对象，采用野外原位实时监测与室内15N标记技术，研究森林土壤NO与N2O的季节排放规律及其对氮沉降的响应；区分土壤硝化与反硝化作用对NO与N2O排放的贡献及其对氮沉降的响应；探明土壤硝化和反硝化来源NO与N2O排放和硝化、反硝化功能微生物丰度的关系。本项目的实施，将有利于准确量化森林土壤NO与N2O的排放，揭示土壤NO与N2O产生的微生物机制，为该区域森林土壤NO与N2O排放及其对氮沉降响应的评估与预测提供理论依据。

一氧化氮(NO)和氧化亚氮(N2O)在氮的生物地球化学循环、大气环境化学和全球变暖中起着重要作用。森林土壤(特别是热带亚热带森林)被认为是NO与N2O排放的一个重要来源。本项目以武夷山不同海拔高度森林(常绿阔叶林、针阔混交林和针叶林)为研究对象，研究了氮沉降对森林土壤NO与N2O排放的影响，并结合室内15N标记技术区分土壤硝化与反硝化作用对N2O排放的贡献及其对氮沉降响应的微生物机制。研究结果表明：(1) 不同森林类型土壤NO对氮添加的响应存在差异，而且响应程度因氮添加量而异。高氮添加显著促进了针叶林土壤NO的排放，但是对混交林与阔叶林土壤NO排放无明显影响。(2) 氮沉降不仅降低了土壤N2O的排放，而且改变了土壤硝化和反硝化来源N2O的排放。森林土壤N2O的排放主要来自反硝化过程，该过程对阔叶林、混交林以及针叶林土壤N2O总的贡献量分别占到了51-87%, 52-65%与63-97%。氮添加增加了反硝化来源N2O的排放，但是降低了硝化来源N2O的排放。在阔叶林、混交林以及针叶林中高氮添加下土壤硝化来源N2O仅占低氮添加下硝化来源N2O排放的17.7%、49.7%以及0.1%。(3)氮添加增加了反硝化来源N2O的排放主要与其增加了土壤中nirK、nirS 基因的丰度以及土壤可利用氮含量有关。硝化来源N2O排放随着氮添加的增加而降低与土壤中较高的NH4+有关，而与土壤中amoA功能基因的变化无明显关系。这些研究结果对于调控亚热带森林土壤N2O具有重要的现实意义，可为评估与预测未来氮沉降对亚热带地区森林土壤NO与N2O排放的影响提供理论依据与数据支持。