超微浮游植物群落在三峡水库典型支流碳循环中作用的研究

Knowledge of key process and mechanism of carbon cycle and autotrophic picoplankton community structure and function is still unclear, which limits us further understanding complexity and uncertainty of carbon ecological process in Three Gorge Reservoir. Using multiple technique and multidisciplinary methods in combination with statistical analysis, typical tributary in Three Gorges Reservoir as study area, primary production, photosynthetic activity in-situ, and community composition, and genetic diversity of autotrophic picoplankton will be studied in order to clarify autotrophic picoplankton community succession, and their adaptation and feedback mechanism to water environment; to quantify the contributions of autotrophic picoplankton to primary production and dynamic correlation among carbon cycle, and via algal physiological experiments, response of different groups of autotrophic picoplankton to higher level CO2 were studied to expound their roles in carbon cycle under the higher level atmospheric CO2, finally, regulation and feedback mechanism between autotrophic picoplankton and key process of carbon cycle will be clarified from multidisciplinary perspective. Research achievements will contribute to accumulating novel scientific cognition on process and mechanism of carbon cycle and nutrient cycle of deep, large reservoir, which has important theoretical guidance significances for ecological civilization construction and sustainable development of the reservoir basin.

目前对于三峡水库碳循环的关键过程与机制和超微浮游植物群落结构与功能的认识尚不清晰，限制了我们对水库碳生态过程复杂性和不确定性的科学认知。项目采用多种技术和学科方法，结合统计学分析，选取三峡水库典型支流为研究区域，开展超微浮游植物初级生产力和光合活性原位实验及群落组成、遗传多样性等调查，阐明三峡库区超微浮游植物的群落演替规律以及对水环境的适应性和反馈调节机制；量化超微浮游植物对水体初级生产力的贡献及其与碳循环过程间的动态耦联；结合模拟大气CO_2水平升高对不同类群超微浮游植物的生理特性影响实验，揭示超微浮游植物在生理学水平对高浓度CO_2的响应机理，从多学科角度明晰超微浮游植物与碳循环关键过程之间的调控与反馈机制。课题成果将有助于在深、大水库碳循环及营养盐循环过程与机制方面积累新的科学认知，对库区流域生态文明建设和可持续发展具有重要的理论指导意义。

目前关于超微浮游植物群落在三峡水库生态系统结构和重要生源要素的生物地球化学循环中的作用尚不明晰，限制了我们对于三峡水库碳循环机制的不确定性和不稳定性的探究。项目以三峡库区三条典型支流为主要研究区域，研究了不同粒径浮游植物对初级生产力的贡献，浮游植物群落和浮游细菌群落的季节变化，解析了影响超微浮游植物初级生产力和浮游细菌群落组成的环境因子，以及两者间的内在联系；分离、培养超微浮游植物藻株，丰富其遗传多样性信息。研究结果表明，朱衣河、草堂河超微粒径部分浮游植物叶绿素a含量自上游至下游逐步升高；大宁河中游表层、水柱超微浮游植物叶绿素a含量均高于下游。自上游至下游，超微浮游植物对水体初级生产力的贡献下降。干流超微浮游植物叶绿素a含量整体低于支流。各支流水温、pH、TP等是影响超微浮游植物叶绿素a含量的主要因子。三条支流浮游细菌群落多样性丰富，包括36门、1762种。变形菌门是优势浮游细菌类群，随季节变化，各支流微生物群落组成和丰度发生变化，春季大宁河浮游细菌群落多样性最丰富，朱衣河最低，冬季大宁河浮游细菌多样性高于春季。变形菌门同水温呈负相关性，其他门浮游细菌随各支流微环境变化而受不同因子的驱动而变化。各支流影响超微浮游植物初级生产力的微生物群落也各有不同，折射出三峡库区水环境的高度异质性对生态系统结构和功能影响的复杂性，碳流途径错综复杂。硅藻门、绿藻门、蓝藻门和裸藻门是梅溪河、朱衣河和草堂河全年分布的主要浮游植物类群，秋、冬季多样性整体高于春、夏季。采用最大似然法和贝叶斯法对分离、培养的藻株进行系统发育分析，确定了1株属于绿藻门、共球藻纲Choricystis属，其余15株属于绿藻门、绿藻纲Mychonastes属，M. rotundus（1株）、 M. afer（2株）、M. homosphaera（1株）以及一未定种（11株），揭示了超微浮游植物丰富的多样性。项目的研究对于深入了解深大水库支流超微浮游植物和浮游细菌群落结构和多样性及其在碳循环中的作用具有重要意义。