河口是陆源物质向海洋输运的主要通道，在全球近岸水体氮污染严峻的形势下，微生物驱动的氮转化过程已成为当前河口复杂环境物质循环研究的热点。最新研究发现悬浮颗粒对河口活性氮削减潜力大，然而悬浮颗粒中微生物驱动的氮转化过程及其对河口环境变化的响应特征仍不明确。因此，本项目拟以珠江口为研究区域，采用同位素示踪技术测定不同粒径悬浮颗粒中微生物驱动的氮转化过程速率及其氮去除贡献率，运用氮循环功能基因扩增子测序、宏基因组学测序和酶联原位荧光杂交等技术解析悬浮颗粒中氮转化微生物的群落组成、生态功能及其空间变异特征，以期发现悬浮颗粒中的新型氮转化过程和氮转化微生物新类群，明确不同粒径悬浮颗粒中微生物驱动的氮转化过程及差异，并阐明悬浮颗粒介导的氮转化过程对河口环境变化的响应特征。本项目的实施将为深入认识河口活性氮的归趋和转化、寻求河口富营养化水体的治理对策提供重要的科学依据。

Estuary is the main channel for the transport of land-based materials to the sea. Under the circumstance of nitrogen pollution in the global estuary water, nitrogen transformation process driven by microorganisms has become a frontier and hot issue in estuary ecology. It is now considered that suspended particulate matter (SPM) plays important roles for reducing reactive nitrogen, and that SPM is a new hot spot for microorganisms involved in nitrogen transformation. However, the relevant research is still in its infancy and especially, there is still a lack of comprehensive understanding of key nitrogen removal processes mediated by microorganisms that are attached to SPM with different particle sizes, as well as the response of these processes to environmental variations. Therefore, the objectives of this proposed study are: (i) to determine the rate of nitrogen transformation processes mediated by SPM with different particle sizes and their contributions to the nitrogen removal in the region from the upper reaches of the Pearl River Estuary to the downstream area by isotopic-tracer analysis; (ii) to examine the diversity, ecological function and spatial distribution of key nitrogen-cycling microorganisms attached to SPM in the Pearl River Estuary by amplicon sequencing, metagenome binning and CARD-FISH approaches; and (iii) to understand how nitrogen transformation processes respond to the variations of environmental parameters. The expected outcomes from this study will discover novel SPM nitrogen transformation processes and new functional microorganisms, clarify key nitrogen-cycling processes of particle-attached microbial communities in the SPM with different particle sizes, and elucidate the response of nitrogen transformation processes in SPS to the changing estuarine ecosystems. Overall, this work will provide the important basic data and scientific basis for understanding the fate and transformation of reactive nitrogen and seeking bioremediation treatment modes for eutrophic water in estuarine ecosystems.