轮虫的分类和功能多样性对湖泊富营养化的响应格局及潜在机制

Eutrophication is still considered to be the most pressing water quality problem in the lower reaches of the Yangtze River. Study on the rotifer community- eutrophication relationships will contribute us to understand the intrinsic effect of eutrophication on the structure and function of biocoenosis. To date, numerous reports have focused on the response of taxonomical α index of rotifer community to eutrophication and made some different conclusions, which was possibly caused by the spatial factors were not involved in such study. However, the research on the response of taxon- and trait-based indices at β diversity level to the changing environmental variables has received less attention. In this project, the shallow lake groups located in the lower reaches of the Yangtze River and Lake Chaohu are planned to be selected as our research sites. By deliberate sampling and analyzing, the indices of taxonomical and functional α and β diversity will be computed. Based on different spatial and temporal scales, our project will be aimed: (1) to analyze the spatio-temporal dynamics of environmental variables and each index of rotifer taxonomical and functional α and β diversity, and to discriminate the trophic level of each lake/lake region; (2) to reveal the quantitative relationships between each of the rotifer α and β diversity index and the trophic level, respectively, and to confirm the pattern of “nestedness or “turnover component of rotifer β diversity index over the gradient of trophic level; and (3) to identify the relative importance of the effects of spatial and environmental variables including wind speed, food resources, potential competitor and predator on the formation of aforementioned patterns. The results will help us to intensively investigate the ecological effects of lake eutrophication on freshwater ecosystem and provide a theoretical reference for understanding the community assembly rules of rotifers. Also, it will bring a scientific base for serving as ecological monitoring and assessment of water quality in shallow lakes.

湖泊富营养化仍是我国长江下游地区重大水环境问题之一。建立在分类/功能的α和β多样性基础上研究轮虫群落-富营养化的关系有助于理解湖泊富营养化对生物群落结构与功能的内在影响。至今多以轮虫的分类α多样性为基础，发现其对湖泊富营养化响应的研究结论存在分歧，与空间变量等未引入可能有关。本项目拟以巢湖和长江下游浅水湖泊群为研究水体，通过多频采样与详细分析，在α和β多样性水平上分别构建轮虫的分类/功能多样性指数，在不同时空尺度上主要研究：（1）上述指数和水环境因子的变动，划分水体的营养水平；（2）轮虫的分类/功能的α和β多样性与营养水平间的定量关系，及其β多样性随营养水平梯度呈现的“嵌套”或“周转”格局；（3）空间变量和轮虫的食物资源、潜在竞争和捕食者等对上述关系和格局形成的相对影响。研究结果为深入探讨湖泊富营养化的生态效应乃至理解轮虫群落构建规则提供理论参考，实践上也服务于湖泊水质的生态监测和评价。

湖泊富营养化仍是全球重大水环境问题之一，其对水生态系统的内在影响受到广泛关注。轮虫作为浮游动物的重要组成部分，理论上其群落结构特征能有效反映湖泊营养水平。然而，现有研究主要集中于轮虫的分类alpha多样性对湖泊营养水平变化的响应，得出的结论并不完全一致。相比分类alpha多样性，仍不确定轮虫的功能多样性特别是功能beta多样性是否与湖泊富营养化间的关系更为密切。本研究按照每季度一次或者两月一次的频次采集并分析了位于长江下游皖苏境内的21个浅水湖泊群（简称湖泊群）及巢湖的水样，基于不同时空尺度研究了轮虫的分类/功能的alpha和beta多样性与水环境因子间的关系。结果表明：（1）水环境因子和轮虫的分类/功能的alpha和beta多样性指数具有显著的时空变化性，综合营养状态指数（TLI）更适合于这些浅水湖泊富营养化水平的评估；总磷（TP）是驱动湖泊群中阻隔性湖泊藻类生物量变动的主要因子，当小型浮游动物密度增长17.5倍后展现了削弱阻隔性湖泊藻类生物量的能力。（2）轮虫的分类/功能alpha和beta多样性与TP间的关系具有尺度依赖性。从周年看，湖泊群中仅轮虫的功能FRic指数随TP变化呈现为“钟形（n）”分布特点；巢湖中轮虫的多数分类/功能alpha多样性指数均与TP间表现出显著的定量关系，且Shannon-wiener指数与TP间关系最为密切。（3）湖泊群和巢湖中轮虫的分类/功能beta多样性对TP变化均不敏感。（4）空间变量对湖泊群和巢湖中轮虫各多样性指数的影响均很小。湖泊群中，相比湖泊营养盐而言，捕食者密度等轮虫的alpha和beta多样性指数的影响更大。巢湖中，轮虫的分类/功能alpha多样性均受水体营养盐的影响最大，而其beta多样性仅在冬秋季受营养盐影响最大，其他季节主要受桡足类密度和水温等影响。（5）湖泊群中轮虫的功能FRic指数和巢湖中的分类Shannon-wiener指数分别在这两类湖泊的营养水平监测中展现了较好的应用前景。研究结果为理解轮虫群落构建规则提供理论参考，实践上也服务于湖泊水质的生态监测和评价。