寄生真菌对巢湖超微型浮游藻类群落结构演替的影响研究

Picophytoplankton, with the cell size less than 3 μm, is an important component in water ecosystems. Our knowledge about this tiny phytoplankton is still limited because of the shortage of the traditional research method due to its small size. Our preliminary results showed that picophytoplankton contributed to more than 50% of total primary production in Lake Chao during the non-bloom period. Meanwhile, the community structure of picophytoplankton showed temporal-spatial variation. Analysis results based on the flow cytometric sorting and high-throughout sequencing, indicated that picophytoplankton is attached with a large amount of fungi, which belong to Chytridiomycota. Furthermore, the zoospore of fungi might specifically attach to particular host picophytoplankton. Chytridiomycota has been found to be the common parasitic fungi on large phytoplankton, but little research reported the host-parasite relationship between picophytoplankton and fungi. Thus, we hypothesized that parasitic fungi may have an important impact on the physiological and ecological traits of picophytoplankton, as well as its community succession. In this study we will perform field investigation to explore the temporal-spatial distribution of picophytoplankton community and their parasitic fungi in Lake Chaohu, and their vital impact factors. The timing of when parasitic fungi impacts picophytoplankton community succession in the field will be determined. The specific relationship between the host picophytoplankton and parasitic fungi on the species level or on the operational taxonomy unit level will be determined. Laboratory incubation experiment will be carried out to explore the parasitic mechanism of fungi on their host picophytoplankton.

粒径小于3μm的超微型浮游藻类是水生生态系统的重要组成部分，由于受其个体微小和传统研究方法的限制，目前对于淡水超微藻的认知还非常有限。我们的初步调查结果表明超微藻在非水华期间对巢湖初级生产力的平均贡献达到了50%以上，并且其群落结构存在显著的时空差异。结合流式细胞分选和高通量测序的结果表明巢湖超微藻细胞上存在着大量的壶菌门真菌，并且两者之间可能存在特异性关系。壶菌门真菌是大型浮游藻类常见的寄生真菌，但其与超微藻寄生关系的相关研究还很少。寄生真菌可能对超微藻的生理生态特性和群落结构演替有重要的影响。本研究拟结合野外调查和室内培养实验，调查巢湖超微型浮游藻类及其寄生真菌群落结构的时空分布特征及关键影响因子，确定寄生真菌影响巢湖超微藻群落结构演替的关键时机；揭示超微藻和寄生真菌之间基于种间水平和遗传多样性分类水平的特异性关系；阐明寄生真菌对宿主超微藻的寄生感染作用机制。

粒径小于3μm的超微型浮游藻类是水生生态系统的重要组成部分，由于受其个体微小和传统研究方法的限制，目前对于淡水超微藻的认知还非常有限。本研究以富营养水体—巢湖为研究对象，进行周年月度的野外调查，结合流式细胞仪分选技术和高通量测序技术，分离纯培养，对巢湖超微真核藻和寄生真菌的物种多样性、演替特征、相互作用及其与环境因子的关系进行了系统的研究。研究结果表明：（1）结合流式细胞仪分选和高通量测序技术，可以很好的降低异养序列在总序列中的比例；巢湖PPEs的多样性较高，包括所有已知门类，但以Chlorophyta 和Bacillariophyta为主，两者共占PPEs总序列数的70%，此外还有Trebouxiophyceae、Chrysophyceae和Dinophyceae等类群存在；巢湖全年PPEs的香农多样性指数峰值出现在12月，各月份间差异极显著；（2）PPEs的群落组成在高分类水平上较稳定，多数样品以Chlorophyceae和Coscinodiscophyceae为优势类群。但在OTU水平，PPEs的物种组成较复杂，不同类群的演替特征有所差异，包括季节演替明显（如环藻和硅藻）、月度演替明显（如团藻和金藻）和月度演替不明显（如绿囊藻）三种情况；（3）巢湖的营养盐浓度空间差异显著，而时间差异不显著，说明巢湖营养盐的空间异质性更为明显。RDA分析显示OTU水平的物种组成主要受水温WT和TN/TP的影响，并且WT可能是群落演替的关键驱动因子；（4）异养序列中Fungi的多样性和丰度是最高的，且夏季藻华及藻华后期（7~9月）Chytridiomycota的序列数占比较高；（5）经流式细胞仪分选后，构建的分子生态网络主要由绿藻门和异养真菌构成，其中Chytridiomycota中的部分OTUs单一的与PPEs存在负相关关系，这种负相关关系意味着它们可能是PPEs的寄生菌；（6）巢湖超微真核藻和寄生真菌可以分为高温组(> 21.8 °C)，中温组（9.8 °C-21.8 °C）和低温组(< 9.8 °C)。随着温度的降低，附着PPEs的真菌与PPEs的相互作用由拮抗变为协同。PPEs附着真菌中OTU最丰富的是最常见的腐生真菌枝孢菌。而真菌中心类群以浮游植物的主要寄生真菌——壶菌门最多。