Spatiotemporal dynamics of bacterial abundance and related environmental parameters in Lake Bosten

于2010年6月-2011年6月在新疆博斯腾湖共进行了9次采样，获得了140份样品，采用表面荧光显微镜直接计数法及广义可加模型（Generalized Additive Models，GAM）研究了表层水体中细菌丰度的时空分布规律及其与环境因子的关系。结果表明博斯腾湖细菌丰度平均值为（1.48±0.95）×10⁶ 个/mL；细菌丰度季节差异显著，夏季最高（2.05×10⁶ 个/mL），冬季最低（3.81×10⁵ 个/mL）。在大湖区，春季和冬季细菌丰度最大值均位于湖区中部，冬季细菌丰度由湖区中部向东南、西南逐渐减少。夏季和秋季细菌丰度分布与春季大致相反，湖区中部较低，西北部较高。GAM分析结果表明，温度、溶解性有机碳（DOC）、叶绿素a、电导率、浊度等5个环境因子对细菌丰度总偏差解释率为81.2%，其中温度贡献最大，贡献率为63.3%，DOC、叶绿素a和电导率，贡献率分别为12.5%、2.7%和1.7%；浊度对偏差的解释率仅为1.0%。在温度超过22℃时，影响博斯腾湖细菌丰度空间分布的主要因子是DOC。;In aquatic systems, bacteria are often closely linked to environmental conditions, which influence the intrasystem bacterial distribution and abundance. To investigate the response of bacterial abundance to environmental factors in lakes located in arid regions, we investigated Lake Bosten in Xinjiang Uygur Autonomous Region, China, which is the largest and most typical inland lake in this region. The inflow of the lake is supplied by melting ice, precipitation and groundwater from the mountainous regions of Tianshan, which formed a salinity gradient from freshwater to oligosaline, making it an ideal model to study the response of bacterial abundance to environmental factors in lakes. Surface water samples from 17 sites of the large-lake area (surface area ≈950 km², mean depth ≈7 m) and six sites of the small-lake area (surface area ≈300 km², depth ≈1-4 m) in Lake Bosten were collected from June 2010 to June 2011. Environmental variables of each sampling site were measured using standard methods. Additionally, the DAPI-combined epifluorescence direct counting method (DAPI-FDC) was used to investigate the bacterial abundance and their spatial and temporal distribution in the lake. The relationship between bacterial abundance and environmental parameters was then explored by the Generalized Additive Model (GAM), which is a flexible and effective technique for modelling nonlinear time-series in studies of effects of environmental factors on organisms. The average abundance of bacteria in Lake Bosten was (1.48±0.95)×10⁶ cells/mL. Generally, bacterial abundance varies from 10⁵-10⁷ cells/L from oligotrophic to hyper eutrophic lakes. Bacterial abundance in mesotrophic Bosten Lake was two times higher than the abundance in oligotrophic lakes during the same season such as Seven Rila Lake in Bulgaria, and in Shield Lake in Canada, while it was slightly lower than that in mesotrophic Lake Schhsee. In addition, the bacterial abundance in Bosten Lake was an order of magnitude lower than that of Taihu Lake and Wuliangsuhai Lake, which are eutrophic. The bacterial abundance also varied significantly with season, with the highest value being recorded in summer (2.05×10⁶ cells/mL) and the lowest in winter (3.81×10⁵ cells/mL). In the large-lake area, the maximum bacterial abundance appeared in the center during spring and winter and decreased from the center to southeast and southwest during winter; however, the opposite spatial tendency was observed during summer and autumn. The result of GAMs showed that temperature, dissolved organic carbon (DOC), chlorophyll <em>a</em> (Chl-a), conductivity and turbidity, explained about 81.2% of the total variation in bacterial abundance in Lake Bosten. Temperature provided the largest contribution to this variation (63.3%), followed by DOC (12.5%), Chl-a (2.7%) and conductivity (1.7%). Our data also showed that, when water temperature was ≥ 22℃, DOC was the most important variable affecting the spatial dynamics of bacterial abundance.

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