达里湖表层水体浮游细菌群落结构的夏-冬季节差异

为探索寒旱区湖泊在夏季非冰封开放、冬季冰冻近封闭等状态差异下表水中典型理化指标和浮游细菌群落结构差异,利用2018年7月和2019年1月采集的内蒙古达里湖41个表水(冰)样品,基于16S rRNA高通量测序和典型理化指标含量分析,讨论了浮游细菌群落结构特征及其对氮(N)和磷(P)元素等理化指标的夏-冬季节差异的响应.首先,夏季表水(夏水)中N和P及电导率(EC)等指标参数相对含量明显高于冬季(包含冬季表水-冬水和湖冰-冰体),且Proteobacteria、Actinobacteria和Cyanobacteria等构成夏水、冬水和冰体中广泛存在的优势浮游细菌门类(相对丰度大于1％).不过,夏水中优势浮游细菌门类数量明显多于冬水和冰体,如Deinococcus-Thermus、Tenericutes和Firmicutes等仅在夏水中为优势菌门;其次,夏-冬季环境条件差异,特别是冬季"冰-水"内部状态改变,不仅引起表水富营养化程度明显差异,还导致优势细菌门类对N和P等营养元素及EC、溶解氧(DO)、冰厚(thickness)和化学需氧量(COD)等理化指标变化产生差异性响应.整体上,虽然聚类及分型结果将样品主要分为冰、水两种类别,且冰体中各理化指标参数对优势菌属相对丰度变化的影响最显著,但冰体优势菌属主要受到结冰过程引起的湖泊内部环境(如不同形态P元素迁移和冰厚等)变化的影响,而冬水和夏水优势菌属则受到外部环境如水深(depth)和溶解性总固体(TDS)等]变化的影响较为明显.

Characteristics of Planktonic Bacteria Community Between Summer and Winter Surface Water in Dali Lake

Lakes are usually influenced by the obvious seasonal changes that occur in cold and arid areas, in which they are nearly completely covered by ice during the winter but receive large amounts of precipitation and other exogenous inputs during the summer. In this study, we collected a total of 41 surface water and ice samples in July, 2018, and January, 2019, in Dali Lake, an inland closed lake located in the Inner Mongolia Plateau. Through 16S rRNA gene-based high throughput sequencing technology, coupled with comparisons of physicochemical proxies between summer and winter surface water samples, the seasonal characteristics of the planktonic bacterial community were analyzed in detail. First, the contents of total nitrogen (TN), total phosphorus (TP), dissolved inorganic phosphorus (DIP), dissolved total phosphorus (DTP), electrical conductivity (EC), and oxidation-reduction potential (ORP) were noticeably higher in summer surface water than those in winter surface water. The results revealed clear seasonal differences in the dominant planktonic bacterial phyla that had a relative content greater than 1%. For example, Proteobacteria, Actinobacteria, and Cyanobacteria were the most dominant phyla in both summer and winter samples. However, Deinococcus-Thermus and Tenericutes were two of the dominant planktonic bacterial phyla that were only present in summer surface water, whereas Gemmatimonadetes was one of the dominant planktonic bacterial phyla present only in winter surface water. Further, the structure of the planktonic bacteria also varied based on the changing of dominant operational taxonomic units (OTUs). Second, the different environmental conditions between winter and summer, especially the exchange process between "ice" and "water," not only caused obvious differences in the eutrophication of surface water but also led to different responses of the dominant bacteria phyla to the content changes in P, EC, DO, COD, ice thickness, etc. For example, the TSI (TP) proxy had higher correlations with changes in the contents of Proteobacteria, Actinobacteria, and Cyanobacteria in ice samples than those in winter and summer surface water samples. Finally, by coupling these findings with the results of sample clustering and typing, we concluded that the dominant bacteria were mainly affected by changes in the internal environment (such as the migration of different P forms, ice thickness, etc.) caused by the freezing process in ice samples. However, the dominant bacteria were mainly affected by changes in the external environment (such as depth, TDS, etc.) in winter and summer water samples.