源头河流砂质基质粒径结构对河流反硝化潜力的影响和关键微生物过程研究

The denitrification potential of headwater rivers got more attention by the researchers, because their length and area are much higher than high-grade rivers. Relative to the high-grade rivers or estuary areas, headwater rivers matrix has more particle size heterogeneity and their particle size structure is easily affected by human activities such as land usage change, dam building, and sand mining. Therefore, matrix particle size structure will be one of the key environmental factors to determine denitrification potential. However, researches relevant to the effects of matrix grain size structure on river denitrification process and related key microbial research are rarely reported. This study intended to choose two typical headwater rivers (poor nutrition VS rich nutrition) as the research object, through field investigation and control experiment (artificial matrix method), combined with isotope pairing technique, quantitative PCR and T-RFLP (terminal-restriction fragment length polymorphism) to explore the effects of sand grain size structure, including size composition and heterogeneity, on river denitrification potential, and at the same time to clarify the denitrifying microorganism community structure and function genes (nirK, nirS) expression. The research will provide new knowledge of denitrification processes and its associated environmental factors and microbial processes in river ecosystem.

由于源头河流的长度和面积占比较高，他们的脱氮潜能越来越受到研究者的关注。相对于高等级河流或河口区域，源头河流基质粒径异质性较大且容易受到人类活动（如土地利用方式转变、筑坝和采砂）的干扰。因此，在研究源头河流的反硝化作用过程中，基质粒径将会是一个关键的环境因子。但是，目前关于河流基质粒径结构对河流反硝化作用和相关的关键微生物过程研究鲜有报道。本研究拟以两条典型源头河流（贫营养VS富营养）为研究对象，通过野外调查和控制实验（人工基质法），结合同位素配对技术、定量PCR及结合T-RFLP技术探究源头河流砂质基质粒径结构（组成和异质性）对河流反硝化潜力的影响，并同时阐明其对反硝化微生物群落结构和功能基因（nirK、nirS基因）表达的影响，本研究将加深我们对河流生态系统反硝化潜力与环境因子和关键微生物过程的认识。

河流沙质沉积物已经被证实为生物地化循环的热点区域。沉积物粒径、流速、上覆水理化特征及沉积物运动等共同驱动了沙质沉积物的生物地化循环过程。本研究聚焦粒径特征对沙质沉积物反硝化过程的影响，通过野外调查实验和野外原位控制实验研究粒径结构变化对反硝化微生物、功能基因和反硝化速率的影响。研究结果表明：无论是中值粒径还是粒径异质性的改变对总微生物（16S rRNA）和反硝化微生物（nirK, nirS, and nosZ）群落结构、反硝化功能基因（nirK, nirS, and nosZ）丰度和反硝化速率均无显著性影响，而上覆水化学特征决定了反硝化微生物群落结构和反硝化速率；反硝化微生物分类单元和反硝化功能基因丰度与反硝化速率解耦合。本研究改变了传统观点粒径特征对氮循环过程的影响，提出了粒径的影响可能存在阈值。本研究结果加深了我们对沙质沉积物氮循环的认识。