三峡大坝对香溪河底栖微生物群落结构和多样性的影响

为了研究三峡大坝修建后库区生态环境的变化,探究大坝修建对库区底泥细菌群落结构和多样性的影响,2013年夏季在香溪河回水区(河口、中游)与河流区(上游)依次选取6个采样点,通过构建16S r DNA基因克隆文库,分析底栖微生物群落结构和多样性的变化规律。结果表明,香溪河调查水域共检出细菌类群15门、87属。在门水平上,回水区和河流区的优势菌门均为变形菌门;在属水平上,回水区和河流区的优势菌属存在显著差异(P0.05),很可能是由于受长江回水和支流高岚河影响所致。芽孢杆菌属所占的比例,从回水区的河口处至中游处逐渐减少至河流区消失,结合芽孢杆菌属易生活在底泥深处的特性,很可能由于大坝的修建,香溪河的上游(即河流区)底泥冲刷至下游(即回水区)河段,被三峡大坝拦截而沉积下来,导致越靠近大坝处,芽孢杆菌属的含量越高。在底泥细菌群落多样性中,Simpson、Shannon和Margalef多样性指数空间分布总体上呈"中间高、两头低"的规律;3种多样性指数最高的采样点均出现在回水区,且回水区的多样性指数均高于河流区,很可能是因其还与旧州河、卜庄河以及周溪河这些支流的交汇,导致河流区底泥细菌群落多样性不稳定。三峡大坝对香溪河底栖微生物的群落结构和多样性产生了显著影响,而大坝修建导致库区回水区水深增加、流速降低、底层水温变化、泥沙沉积增加等因素是造成这种差异的可能原因。

Impacts of Three Georges Dam on the Structure and Diversity of the Benthic Microorganism Community in Xiangxi River

The construction of Three Gorges Dam produced significant impacts on the ecology of the Yangtze River, particularly in Three Gorges Reservoir (TGR). However, effects on benthic microorganisms are not known. To evaluate the effects of damming on benthic microorganism community structure and diversity in Three Gorges Reservoir, we investigated the benthic microorganism community at six sites in Xiangxi River by constructing a 16S rDNA clone library. Sites 1-4 were in the tributary cove of Xiangxi River, influenced by the backwater of TGR, while Site 5 and Site 6 were in the middle and upper reaches of Xiangxi River. On June 25 of 2013, sediment samples were collected from the six sites and a total of 87 bacterial genera belonging to 18 phyla were identified. The most dominant phyla in both backwater and riverine regions were Proteobacteria, but the dominant genus in the backwater and riverine regions were different, probably caused by backwater from TGR and the inflow of Gaolan River. The proportion of Bacillus gradually decreased from cove to midstream backwater regions and no Bacillus was found in the riverine section. Bacillus prefer deep sediment and the sediments from the upper Xiangxi River are retained in the backwater regions by damming, providing good habitat for Bacillus. The ranges of the Simpson, Shannon and Margalef diversity indices of the bacterial community in Xiangxi River were, respectively, 0.8673-0.9492, 2.107-3.039 and 3.031-6.762. All diversity indices at Site 1 and Site 6 were lower than at other sites, displaying a parabolic distribution. The highest Simpson and Shannon diversity indices both occurred at Site 2 and the highest Margalef index occurred at Site 3. The diversity indices in backwater regions were higher than those of in the riverine region, except for Site 1. This is attributed to the tributaries (Jiuzhou, Buzhuang and Zhouxi Rivers) flowing into the riverine section of Xiangxi River and disrupting the sediment bacterial community. Three Gorges Dam significantly affects the structure and diversity of the benthic microorganism community in Xiangxi River. The factors responsible for the impacts include increased water depth, decreased velocity, change in bottom water temperature and increased sediment deposition in the backwater area.