海草根系是叶片-根系-沉积物碳流动过程的关键联系纽带，根系分泌与分解释放溶解有机碳（DOC）是海草床沉积物有机碳的重要来源。人类活动引起的近岸海域无机氮增加，可能会改变海草根系分泌与分解释放DOC的过程，进而对沉积物储碳能力产生影响。因此，探讨氮对海草根系分泌与分解释放DOC的影响机制极为重要。本项目以热带海草优势种泰来草（Thalassia hemprichii）为研究对象，通过现场观测，弄清泰来草的根系形态、生物量、碳成分特征及其与氮的关系；同时结合室内模拟和原位实验，研究泰来草根分泌DOC占光合固定碳的比例及其对氮的响应，阐明海水氮和沉积物氮对泰来草根系形态、碳成分、根分泌DOC速率的影响，阐释环境氮和根的氮含量对泰来草根分解速率和DOC释放速率的影响。本项目将有助于揭示氮对泰来草根系碳流动过程的影响机理，加深认识富营养化对海草床储碳关键过程的影响机制。

Seagrass roots are the key link of carbon flow between leaf-root-sediment. The release of dissolved organic carbon (DOC) from seagrass roots through exudation and decomposition is a vital source to the sediment organic carbon in the seagrass beds. The increase of inorganic nitrogen in coastal waters caused by human activities may change the process of DOC exudated from seagrass roots and DOC release during the decomposition of seagrass roots, thereby affecting the sediment carbon storage capacity in the seagrass beds. Therefore, it is very important to explore the effect of nitrogen on the release of DOC from seagrass roots through exudation and decomposition. In this project, we will select Thalassia hemprichii, the tropical dominant seagrass specie, as the research object. Through field investigation, the characteristics of root morphology, biomass, carbon composition and their relation with nitrogen would be observed. With the combination of laboratory simulation and in-situ experiments, the ratio of DOC exudated from roots to photosynthetically fixed carbon and its response to nitrogen, the effect of seawater nitrogen and sediment nitrogen enrichment on the root morphology, carbon composition, DOC exudation rate, the effect of environmental nitrogen and root nitrogen on the decomposition rate of root and its DOC release rate would also be examined. This project will help us to reveal the mechanism of nitrogen effect on carbon flow in the root systems of T. hemprichii, and to deepen the understanding of the effect of eutrophication on the key process of carbon storage in the seagrass beds.