Spatial distribution of bacterioplankton community composition and their diversity in Lake Fuxian during thermal stratification period

Abstract

水体垂向分层是深水湖泊一个重要的特征，这不仅影响水体理化环境因子，而且影响水生生物组成的垂向分布，但是对不同水层水体细菌的多样性和群落结构组成的形成与维持机制知之甚少. 本研究以抚仙湖为研究对象，在水体热力分层期间采集不同位点、不同水层水样，借助16S rDNA Illumina Miseq高通量测序技术，探究水体细菌多样性和群落结构组成的空间分布特征及关键影响因子. 研究结果表明：(1)抚仙湖北部湖心在水深15~40 m处出现温跃层，温度由23℃降至15℃，其余理化环境因子也存在明显的垂向分层现象；与垂向差异相比，表层水体各理化因子在水平方向上的差异相对较小. (2)在水平方向上，南部湖心表层水体细菌alpha多样性(Operational Taxonomic Unit数目和Faith's phylogenetic diversity)最高；在垂向上，水体细菌alpha多样性随着采样水深的增加呈现单峰分布，在30和40 m水层最高；水体细菌alpha和beta多样性的垂向差异均显著大于水平方向差异. (3)表层水体细菌主要由Actinomycetales、unidentified Cyanobacteria、Burkholderiales和Sphingobacteriales组成；温跃层中以Pseudomonadales为主；均温层的优势菌群为unidentified Chloroflexi、Actinomycetales和Burkholderiales. 典范对应分析表明溶解性有机碳、溶解氧、硝态氮、氨氮和总磷浓度是影响细菌群落组成的主要环境因子.;Deep lakes are typically characterized by thermal stratification throughout the year, except for a short mixing period in winter. This vertical partitioning has important effects on many biotic, physical and chemical characteristics of the water column. However, at present, little is known about how these changes affect the vertical distribution of bacterioplankton community diversity. In this study, Lake Fuxian with a relatively long thermal stratification period every year, was chosen for the investigation of bacterioplankton distribution, diversity and composition on August 25th, 2013. 16S rDNA Illumina Miseq high-throughput sequencing technology was performed on DNA extracted from water samples collected from different locations and different water depths. The results showed that: (1) A thermocline appeared in the lake center and in the northern part of this lake at the depth of 15-40 m, with the temperature dropping from 23℃ to 15℃. Other physical and chemical factors also showed obvious vertical stratification pattern. Horizontally, there is no significant difference in physicochemical features. (2) In the horizontal direction, the alpha diversities of plankton bacteria (the number of Operational Taxonomic Units and Faith's phylogenetic diversity) in the surface water of the southern lake center was the highest; in the vertical direction, the alpha diversity gradually increased with the increase of the sampling depth, topping at the depths of 30 m or 40 m, and then gradually decreased; the difference of the bacterioplankton alpha and beta diversity in the vertical direction was significantly greater than those in the horizontal direction. (3) The bacterioplankton in the epilimnion were mainly composed of Actinomycetales, unidentified Cyanobacteria, Burkholderiales and Sphingobacteriales; the relative abundance of Pseudomonadales in the thermocline significantly increased and became dominant; unidentified Chloroflexi, Actinomycetales and Burkholderiales were the dominant bacterial taxa in the hypolimnion. The canonical correspondence analysis demonstrated that the concentrations of dissolved organic carbon, dissolved oxygen, nitrate, ammonium and total phosphorus are the significant environmental variables shaping the bacterial community's composition and diversity.