水位波动下三峡水库消落带土壤N2O排放及其对团聚体演变的响应机制

Soil moisture is a dominant factor influencing nitrous oxide (N2O) production and its emission. Drying and re-wetting cycles, a most frequently experienced process for changes on soil water regime, generally induces alteration on soil structure and spatial distribution of water and heat in soil. Accordingly, nitrifiers and denitrifiers re-distribute on different sizes of aggregates and hence impacts N2O production and its transportation. However, the community structure of nitrifiers and denitrifiers on different sizes of aggregates and their influences on N2O emissions remains unknown as impacted by drying and re-wetting cycles. In this project, field experiment and on-site sampling, coupled with lab incubation and tests will be selected to investigate the N2O fluxes and their responses to soil aggregate turnover as influenced by water level fluctuation in the typical drawdown zones of the Three-Gorges Reservoir. N2O fluxes and their influencing factors will be observed along the different elevations of drawdown zones to reveal the tempo-spatial dynamics of N2O emissions and their dominant factors. Soil aggregates sieving and lab incubation will be used to investigate the relative contributions of N2O emissions for different sizes of aggregates as well as the potential hot-spots of N2O production. The heterogeneity of nitrifiers and denitrifiers on different sizes of soil aggregates as influenced by water level fluctuation and their effects on N2O emission will be determined by quantitative PCR and Sequencing. Such results will be conducive to improve our knowledge on the influence of soil structure on nitrogen transformation and cycling in the newly formed eco-system. Regional nutrients management is also expected to benefit from the current proposed research.

水分状况是影响土壤N2O产生和排放的重要因素。干湿交替是土壤最频繁经历的水分变化过程，其导致的土壤结构改变必然引起水热状况再分布，相应地改变硝化反硝化微生物在不同粒径团聚体上的种群和丰度，进而影响N2O产生和传输。然而干湿交替下，不同粒径土壤团聚体硝化反硝化微生物群落结构变化及其对N2O产生和排放的影响，目前尚不清楚。本项目拟选取三峡水库典型消落带为研究对象，通过原位观测不同高程土壤N2O排放通量，揭示周期性干湿交替下消落带土壤N2O排放规律及其影响因素；通过团聚体筛分和室内培养明确不同粒径土壤团聚体对N2O排放的相对贡献与N2O产生热区；运用功能基因定量分析和高通量测序等技术，阐明水位波动下硝化反硝化微生物在不同粒径土壤团聚体的群落结构分异规律及其对N2O排放的影响。对于进一步认识土壤结构演变对氮转化的影响机制具有重要理论价值，也可为生态系统氮循环研究和养分管理提供基础资料和理论支撑。

氧化亚氮（N2O）是重要的温室气体, 土壤是N2O排放的重要来源。水分状况是土壤N2O产生和排放的重要环境影响因素。周期性水位波动是水库消落带土壤最频繁经历的水分变化过程，其导致的土壤结构改变必然引起水热状况再分布，相应地改变硝化反硝化微生物在不同粒径团聚体上的种群和丰度，进而影响N2O产生和传输，最终导致N2O排放的差异。本项目选取了三峡水库澎溪河土质消落带为研究对象，通过长期原位观测不同高程和土地利用方式下土壤N2O排放通量，发现中度水淹胁迫下（165 m左右）消落带土壤是N2O在空间排放的热区，土地利用、表层土壤温度和碳氮赋存形态与浓度是消落带土壤N2O排放的主导因素；通过团聚体筛分和室内培养，明确不同粒径土壤团聚体对N2O排放的相对贡献，探明了小团聚体是消落带土壤N2O产生和排放的热区；运用功能基因定量分析和高通量测序等分子生物学技术，量化了N2O产生和还原的功能基因，解析了携带功能基因的微生物群落多样性，发现了反硝化作用的功能微生物群落多样性高于硝化作用的功能微生物，阐明了功能基因在不同粒径土壤团聚体中的分布趋势及其与N2O排放的关系，还筛选出调控N2O排放功能基因的关键物种类群。该结果对于进一步认识极端环境胁迫条件下土壤结构演变及其对氮转化的影响机制具有重要理论价值，也可为生态系统氮循环研究和养分管理提供基础资料和理论支撑。