洞庭湖超微型浮游藻类多样性及其关键影响因子研究

Picophytoplankton (≤ 3 μm) are key components of the plankton systems and play important roles in substance circulation and energy flow of the aquatic ecosystems. Even in eutrophic lakes, their contributions to total plankton production can averaged at 30% in the whole year, and peaked at 70% during non-bloom periods. The eutrophic Lake Dongting is an important open lake connected with Yangtze River in the middle reach, and is characterized with water carrying possessing unique hydrological conditions. Compared with other Yangtze-unconnected lakes, Lake Dongting may contain distinct picophytoplankton diversity. However, until now no studies have reported on it. We will perform field investigation, combined with flow cytometry and high-throughput sequencing techniques, to study the temporal and spatial patterns of the diversity and community composition of picophytoplankton in Yangtze-connected lake, Lake Dongting. The results will be further compared with the study conducted in Yangtze-unconnected lakes, Lake Taihu and Lake Chaohu. The key factors impacting picophytoplankton community, especially the influences of contacted heterotrophic microorganisms on picophytoplankton will be revealed. Our results will be conducive to understand the role and diversity of picophytoplankton in aquatic systems with different properties and enrich the ecological theories such as inter-species relationship and key microbial functional groups.

超微型浮游藻类(≤ 3 μm)是浮游生态系统的重要组成部分，在水体物质循环和能量流动中起着重要作用，即使在富营养化湖泊中，其对初级生产力的年平均贡献可高达30%，非水华季节的贡献可达到70%以上。洞庭湖是长江中游重要的过水性洪道型湖泊，具有独特的水文动力条件；相对于半封闭性湖泊，洞庭湖可蕴含特殊的超微藻多样性，目前对其的研究还是空白。本项目拟通过野外调查，结合流式细胞仪和高通量测序技术，揭示大型通江湖泊洞庭湖超微藻多样性和群落组成的时空分布特征，并与半封闭性湖泊太湖、巢湖的研究结果进行比较；弄清影响洞庭湖超微藻群落组成变化的关键因子，特别是关联异养微生物对超微藻的影响。该研究将有助于深入认识超微藻在不同生境类型水体中多样性的维持机制及生态意义，丰富种间关系和关键微生物功能群等生态学理论。

超微藻(≤3μm)是浮游生态系统的重要组成部分，由于其个体微小和受传统研究方法限制，目前对于淡水超微藻的认知还非常有限。本项目以通江性洞庭湖为研究对象，通过周年野外调查，结合流式细胞仪和高通量测序技术，对洞庭湖超微藻及其关联异养微生物的多样性、群落组成、相互作用及与环境因子的关系进行了系统研究。研究结果表明：①洞庭湖超微藻全年平均浓度为5.52μg L-1，平均占总浮游藻类生物量的31%。超微藻在总浮游藻类中的占比与氨氮、DO和NTU显著负相关，与TP、SD、T和WL等显著正相关；②洞庭湖超微真核藻（PPEs）和超微蓝藻（PCY）全年平均丰度分别为21和61cells µL-1，二者均表现出显著的时空差异(p<0.05)；③丰水期超微藻以PCY为主，PCY:PPEs平均值为3.4，WL、N:P、TN和T是其关键影响因子。④洞庭湖PCY主要为聚球藻。而PPEs多样性极为丰富，主要以硅藻和绿藻为主，合计占比67%；此外，黄群藻、金藻、隐藻和硅鞭藻等也较为丰富。PPEs多样性在秋、春季达到峰值。⑤洞庭湖PPEs优势类群以Discostella和Poterioochromonas属为主，而太、巢湖主要以Stephanodiscus属为主。⑥洞庭湖PPEs附着细菌以变形菌、放线菌、拟杆菌和蓝细菌为主，合计占比90%；而关联异养微生物（NPEs）以真菌为主，占比63%。⑦洞庭湖PPEs及其关联微生物的群落组成均表现出显著的时间演变规律(p<0.05)，而空间差异不显著(p>0.05)。⑧PPEs及其关联微生物共现生态网络表明它们之间的互作关系具有显著的时间演变规律。相对于NPEs，PPEs与附着细菌之间联系更为紧密；且它们之间可能不具特异性联系。⑨统计分析发现附着细菌对PPEs群落变化的解释率最高（27.8%）。相比环境因子，关联微生物对PPEs群落变化的影响可能更为重要，尤其是附着细菌。