深海微生物氨氧化过程通过化能自养固定无机碳，是深海系统中的重要能源途径，直接影响深海的碳储库。氨氧化古菌的发现，对这一生物地球化学过程的传统认识提出了新的挑战，带来了新的科学问题。本项目以南海深海为目标研究海域，采用海洋地球化学、分子生态学及稳定同位素示踪等多学科交叉的技术手段，基于从微观到宏观的研究思路，通过测定关键地球化学指标以及自养固碳率，厘清南海深部特征水团微生物氨氧化自养固碳的地球化学过程；并基于关键功能基因的指示，分析氨氧化功能微生物在深海中化能自养固碳的分子生态学机制；同时运用SIP和微宇宙培养技术，甄别不同水团氨氧化细菌和氨氧化古菌自养固碳力的大小；最后通过理论和实际分析对比，探索影响深海微生物氨氧化自养固碳的关键环境因素。本研究将深化对深海暗能量生物圈氨氧化微生物驱动自养固碳机制的认识，拓展海洋深部生命活动中碳-氮循环过程的关系，为更合理的评估海洋碳储库提供理论支撑。

Nitrification, the two-step oxidation of ammonia to nitrate via nitrite, plays a critical role in the global carbon cycle by fixing CO2 with the form of chemolithoautotrophy, and consequently influencing the organic carbon pool and food web structure in the dark ocean. It has long been assumed that the first and rate-limiting step of nitrification, ammonia oxidation, is restricted to a few groups within the domain Bacteria. However, the recent discovery of ammonia-oxidizing Archaea (AOA) has seriously challenged our understanding of the microbial ecology and biogeochemistry of nitrification in the ocean. Therefore, the biogeochemical mechanism of CO2 fixation by microbial nitrification is large unknown. .In order to lighten the relationship between the microbial nitrification and chemolithpautotrophy carbon fixation in the deep sea, a series studies on the typical tropical marginal sea, SCS, will be carried out by integrating the methods from oceanography, ecology, biogeochemistry and molecular biology. The specific objectives are to: (1) quantify carbon fixation rate by nitrification with multi-biogeochemical parameter in the water masses of deep SCS; (2) examine molecular mechanism of chemolithpautotrophy carbon fixation by important microbial nitrifer communities,including ammonia oxidation bacteria (AOB) and ammonia oxidation archeaa(AOA)(3) determine if ammonia oxidation archaea (AOA) play a dominant roles in fixing inorganic carbon in the deep sea based on uptake of 13C-labeled bicarbonate into archaeal genome DNA under microcosm system; (4)estimate the key environmental factors influencing this biogeochemical process..The project will be helpful to expand and strengthen the existing oceanographic carbon-nirogen network, to increase our understanding on microbial and biogeochemical process of autotrophic production by marine nitriication. Ultimately, this multi-disciplinary study should provide insights into the ecological significance of this biogeochemically-important process in all marine systems.