生物固氮对西沙珊瑚礁区海草的促生作用及其在恢复岛礁生态系统中的重要性

西沙珊瑚礁是典型的热带大洋型珊瑚礁，代表着我国现存最古老和最珍贵的珊瑚礁，具有不可估量的社会经济价值。先锋植物海草具有抑制岛礁荒漠化和防止珊瑚礁盘崩塌的重要科学意义。本项目拟着重对能够促进先锋植物海草生长的生物固氮作用展开详细的研究；定期调查西沙永兴岛、西沙洲和赵述岛周边选定海域内的海草种类及其分布特征；利用乙炔还原法，测定固氮微生物的原位固氮效率并估算氮贡献量；利用固氮基因nifH的特异性引物，构建基因文库分析固氮微生物群落变化并应用荧光定量PCR法分析固氮微生物的丰度变化和基因表达特性；测定相应海草的生物量和含氮量，并计算其生产力；利用多元统计方法，探讨环境变化对海草生长、原位固氮效率和固氮微生物群落与功能的影响，并深入探究生物固氮与海草生长之间的关系。该研究结果不仅将揭示生物固氮对先锋植物海草生长的促进作用，推动我国珊瑚礁区海草的研究，而且将为恢复岛礁生态系统提供科学依据和技术支持。

Coral reefs of Xisha Islands are typical oceanic coral reefs. They represent the oldest and rarest coral reefs in China and have immeasurable social and economic values. Pioneer plants seagrass can inhibit reef desertification and prevent coral reef collapse, so they are of great importance. Entensive inverstigation in this project will be carried out to study the biological nitrogen fixation which can promote the seagrass growth. Regular survey of the species and distribution pattern of seagrass in the selected areas around Yongxing Island, Xisha Zhou and Zhaoshu Island will be conducted. In the meantime, acetylene reduction assay will be applied to mearsure the in situ nitrogen fixation rate, and the total nitrogen fixed by epiphytic organisms will also be estimated. Based on nitrogenase gene nifH, clone library will be constructed to investigate the the dynamics of nitrogen fixing bacterial community structure and fluorescence quantitative PCR will be employed to analyze the abundance and gene expression of nitrogen fixing microorganism. Biomass and nitrogen content together with enviromental factor of the surronding water and pore water of sediments the will be measured. The productivity of seagrass will be calculated based on the data obtained. Multivariate statistical analysis will be used to study the effect of environmental change on the seagrass growth, nitrogen fixation rate and the nitrogen-fixing bacterial community structure and function, and exlore the relationship between biological nitrogen fixation and seagrass growth. The results of this project will not only reveal the role of biological nitrogen fixation to seagrass growth and promote the study of seagrass and coral resources in China, but also will provide scientific basis and technical support for the reef island ecosystem restoration.