海水入侵区含水层中原核微生物多样性和群落结构特征及其意义

海水入侵引起的地下水咸化是沿海地区面临的主要自然灾害之一，并由此产生了强烈的物理化学梯度变化，严重影响了原生态环境. 为研究海水入侵影响下含水层微生物的多样性和群落结构，揭示海水入侵对原位微生物群落的环境影响，采用基于高通量测序的微生物群落分析方法，对珠江三角洲含水层中微生物群落多样性和结构组成进行表征和比较，并探讨微生物群落对环境变化的响应. 结果表明:研究区地下水中微生物群落主要分属于47个原核微生物门类，其中最丰富的门是变形菌门(Proteobacteria)，其次是厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)和拟杆菌门(Bacteroidetes)，而古菌的群落结构以奇古菌(Thaumarchaeota)和广古菌(Euryarchaeota)为主，且Thaumarchaeota和Euryarchaeota在高浓度咸水中丰富度更高. 不同盐度梯度下微生物群落之间共有的OTUs占比为59%，在一些高浓度咸水样品中存在大量的脱硫弧菌属和甲烷球菌厌氧微生物. 虽然微生物群落的多样性并不完全与盐度梯度一致，但在溶解性总固体(TDS)浓度大于1 g/L的含盐地下水中，微生物群落的多样性随盐度的增加而增加. 典范对应分析(CCA)表明，TDS和总氮(TN)是影响微生物群落分布最显著的环境因子. 研究结果为进一步揭示海水侵蚀下的地下水中微生物群落的结构及其环境相互作用奠定了基础. 

Diversity and Structure of Prokaryotic Microbial Community in Seawater Intrusion Aquifers and Its Significance

The salinization process of groundwater caused by seawater intrusion is one of the major natural disasters in coastal areas. It generates a salt-fresh water interface with a strong physicochemical gradient, which seriously affects the original ecological environment. Therefore, an in-depth understanding of the diversity and community structure of microorganisms in aquifers affected by seawater intrusion is essential to reveal the environmental impact of seawater intrusion on in-situ microbial communities. Here, we utilized high-throughput sequencing-based microbial community analysis to characterize the diversity and composition of prokaryotic microbial communities and explore the response of microbial communities to the brackish aquifers subjected to seawater intrusion. The results showed that there were 47 prokaryotic microbial groups in the groundwater of the study area. Proteobacteria was the most abundant, followed by Firmicutes, Actinobacteria and Bacteroidetes, whereas the community structure of Archaea was dominated by Thaumarchaeota and Euryarchaeota which were more enriched in high concentration saline water. The common OTUs in microbial communities of different salinity gradients accounted for 59%, and there were abundant anaerobic microorganisms of genera Desulfovibrio and Methanococcus in some high concentration saline water. Although the variation of microbial diversity was not completely in parallel with the salinity gradient, the diversity increased with increasing salinity with total dissolved solids (TDS) above 1 g/L. A vector fit of possible explanatory environmental factors highlighted that TDS and TN were the most significant factors for the separation of microbial assemblages along the salinity gradients. It should be noted that high levels of ammonia nitrogen in the aquifer may affect the ecological balance to a certain extent. This study provided a foundation for further study of microbial community structure and environmental interaction in underground saltwater.