海草床系统底栖氮循环微生物多样性及活性的研究

Seagrass bed, a well-known marine Blue-Carbon system, is one of the most highly productive coastal ecosystems on Earth. However, our knowledge on benthic nitrogen cycling in seagrass systems is still limited. Benthic nitrogen cycling includes multiple interface-related oxic, anoxic, autotrophic and heterotrophic processes, such as these between water and sediment, and between plant root and sediment. Previous studies have demonstrated that seagrass roots release photosynthesis-produced organic matters and O2 to sediments, which results in high dissolved organic carbon (DOC) and less-reducing conditions around roots and in seagrass meadows, compared with bulk sediments and seagrass-free areas. How these spatial and temporal heterogeneity affect the diversity, distribution, dynamics, and activities of nitrogen-cycling microorganisms remains to be studied. This project seeks to address this question by using a combination of biogeochemistry and microbial ecological methodologies: the rates of denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) will be determined using stable isotope (15N) technique, and functional genes and their transcripts (amoA，nirS, nirK, nosZ, nrfa and hzo) will be investigated using a range of molecular techniqies such as high throughtput sequencing, clone library, and quantitative PCR or RT-qPCR. Diversity, composition, copy numbers of gene and transcripts will be characterized to examine the effects of location (vegetated and unvegetated sediments) and diurnal and seasonal variations. Our overall objective is to better understanding the nitrogen cycling and regulating factors in this system, which may be vital to maintain and restoration of this important ecosystem in our coastlines.

海草床是海洋蓝碳系统的重要组成，也是近海生产力最高的生态系统之一，但对其沉积物中微生物多样性及其驱动营养盐循环规律的了解还非常有限。底栖氮循环存在于水-沉积物、根系-沉积物等多个界面，包括自养、需氧和异养、厌氧过程。海草光合作用向根际分泌有机质和氧气，使沉积物中的有机碳及氧化还原状况表现出强烈的时空异质性，这些因素如何影响底栖微生物氮循环是该生境中营养盐再生与转化研究的一个核心问题。本项目拟以山东荣成大叶藻海草床为研究对象，利用15N稳定同位素技术和高通量测序、克隆文库及定量PCR手段比较研究海草床沉积物反硝化、厌氧氨氧化、硝酸盐氨化速率和相关功能基因多样性、数量及其表达情况的空间（草区和裸露区）和时间（季节、昼夜）异质性，揭示海草床底栖氮循环过程及微生物群落组成、活性的时空变化特征和主要调控因子。研究结果将为海岸带生态系统的微生物过程与物质循环机制研究、海草床的保护与恢复等提供必要参考。

海草床是海洋蓝碳系统的重要组成，也是近海生产力最高的生态系统之一，但目前人们对其沉积物中微生物多样性及其驱动营养盐循环规律的了解还非常有限。底栖氮循环存在于水-沉积物、根系-沉积物等多个界面，包括自养、需氧和异养、厌氧过程。海草为维持巨大的生物量，需要大量氮营养补充；海草定植减缓海水流速，促进区域颗粒有机质的沉降；其光合作用向根际分泌有机质和氧气，使沉积物中的有机碳及氧化还原状况表现出强烈的时空异质性；这些因素如何影响海草床系统底栖微生物驱动的氮循环是该生境中营养盐再生与转化研究的一个核心问题。.本项目拟以山东荣成大叶藻海草床为研究对象，利用15N稳定同位素技术结合高通量测序、克隆文库及定量PCR等分子生态学手段比较研究海草床沉积物反硝化、厌氧氨氧化、硝酸盐氨化速率和相关功能基因多样性、数量及其表达情况的空间（草区和裸露区）和时间（季节、昼夜）异质性，揭示海草床底栖氮循环过程及微生物群落组成、活性的时空变化特征和主要调控因子。主要成果如下：海草定植明显促进沉积物的硝化、反硝化和厌氧氨氧化活性；其中氨氧化细菌（AOB）和反硝化菌分别是硝化和脱氮（产生N2）过程的主要贡献者；草区固氮菌的丰度显著高于裸露区，且该区域的优势细菌倾向于降解小分子活性有机质，而裸露区的优势细菌则主要倾向于分解大分子惰性有机质；随着海草不同季节生长状态的变化，沉积物细菌、古菌及氮循环微生物的丰度和群落结构都表现出显著的季节特征；由于海草床沉积物剖面呈现出表层氧化态且活性有机质丰富到深层还原态以惰性有机质为主的垂直梯度特征，其中的细菌和古菌的丰度、多样性和群落分布也表现出明显的垂直特征。有机质质量、无机氮营养、溶解氧等是影响海草床氮循环微生物活性和群落结构的重要因子。.以上研究结果将为海岸带生态系统的微生物过程与物质循环机制研究、海草床的保护与恢复等提供必要参考。