典型滨海流域河流沉积物硝酸盐转化主导途径演变及分子驱动机制

This project will integrate the biogeochemical hot spot – hot moment principle and laboratory cultivated simulations to investigate watershed – scale variations in the contribution of different transformation paths to nitrate removal in river sediments, the structure and composition of functional microbial communities (functional genes) involved in nitrate transformations, and nitrogen cycling rates at different hot spots confluences of different subwatersheds characterized by variable oxidation reduction potential driven by different environmental factors). A functional molecular ecological network will be developed to quantify the cooperation and competition relationships among functional microbial communities. Nitrate transformation paths will be characterized based on nitrogen cycling rates and the structure and composition of functional microbial communities. Spatial and temporal variations in nitrate transformation paths will be compared by collecting surficial sediment samples at different water periods (dry season and wet season) and sites (hot spots). By coupling with anthropogenic nitrogen inputs of a subwatershed, quantitative response of the variations in dominant removal paths for nitrate at the hot spot will be explored. Critical environmental factors will be identified and molecular driving mechanisms will be revealed based on the theories of microbial molecular ecology and watershed natural geography. Results of this project will provide a high precision analysis method for watershed nitrogen pollution estimation and contribute to watershed nitrogen cycling regulation and management under the goal of sustainable development.

本项目以河流沉积物为对象，应用hot spot - hot moment生物地球化学原理，结合室内模拟培养，研究流域尺度下不同热点（hot spot）（不同环境因子驱动的氧化还原电位变化的子流域汇流点）下沉积物硝酸盐转化不同途径的贡献、相应功能微生物群落（功能基因）结构组成演变和氮循环速率变化；构建氮循环关键功能基因分子生态网络，解析功能微生物群落之间的协作竞争关系；以氮循环速率和相应功能微生物群落结构量化表征沉积物硝酸盐转化途径，探索实验流域不同时期（枯水期和丰水期）各子流域汇流点沉积物硝酸盐去除途径的时空演变规律；耦合流域人为源氮输入，构建沉积物硝酸盐去除主导途径演变的定量响应模型，综合微生物分子生态学和流域自然地理学理论，甄别关键环境影响因子，揭示其分子驱动机制。本项目的完成将为流域氮污染估算提供高精度解析方法，为可持续发展目标下流域氮循环调控和管理提供科学依据。

随着城镇化进程加快，过量的氮输入使得流域氮循环过程失衡，并造成一系列生态环境问题。硝酸盐是生态系统去除过量氮素重要生物化学过程的底物。然而，由于硝酸盐去除途径并不单一，途径间的交替、功能微生物群落演替和活性调控机制尚不明确。本项目结合室内模拟培养，研究流域尺度下沉积物硝酸盐转化不同途径的贡献、相应功能微生物群落演变和氮循环速率变化；构建氮循环分子生态网络，解析群落之间的协同竞争关系，并甄别关键影响因子。结果表明，表层沉积物对上覆水硝酸盐的热力学吸附集中在反应开始后的前20 min；硝酸盐浓度（CNO3）和氧化还原电位（Eh）对反硝化速率（PDA）和厌氧氨氧化速率（AMX）具有显著影响（P < 0.05），且相同初始条件下PDA和AMX因子流域类型不同而有所差异。九龙江流域表层沉积物反硝化作用对硝酸盐的去除贡献为75.33 ± 12.14%，大于厌氧氨氧化作用，且这种差异在丰水期有所减小。细菌16S丰度大于古菌（P < 0.05），且受水文条件变化的影响较大，此外，nirK、nirS、nosZ和hszB丰度在北溪最大，且主要集中在丰水期。基于SEM模型发现，水体环境因子通过影响基因丰度间接影响PDA和AMX，其中，nirS和hszB分别是PDA和AMX的关键影响因子。nosZ序列在北溪以Polymorphum属为主，nirS序列中，北溪和南溪以Azoarcus属占比最大。城镇、绿地、农业和森林子流域分子生态网络中的关键类群分别为Firmicutes、Proteobacteria、Cyanobacteria和Actinobacteria。种群之间存在一定的非随机共存关系，且TC在枯水期的连通性最高，而TOC在丰水期的连通性最高。研究结果为可持续发展目标下流域氮循环调控和管理提供科学依据。