[Changes in the Bacterioplankton Community Between "Ice" and "Water" in the Frozen Dali Lake]

Bacteria are the key components of water ecosystems, and play important roles in material and energy cycle processes. To understand the changes in the bacterioplankton community in frozen lakes, we collected 15 "bottom ice" samples and 15 "surface water" samples under the ice sheet from Dali Lake, which is an inland closed lake in the Inner Mongolia Plateau. Combined with comparisons of the physicochemical proxies between "bottom ice" and "surface water" samples, the phylum community characteristics of the bacterioplankton were analyzed in detail. Although the bacterioplankton were mainly comprised of Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and 11 other phyla in the "bottom ice" and "surface water", the average relative abundances of the dominant planktonic bacteria were clearly different. For example, the average relative abundance of Proteobacteria was approximately 63.64% in the "bottom ice" samples, but decreased to approximately 26.75% in the surface water samples, which was visibly smaller than the relative abundance of Actinobacteria with an average value of approximately 39.10%. We concluded that the changes in the contents of nutrient elements and physicochemical proxies must be the primary factors influencing the changes in the bacterioplankton community in the frozen Dali Lake. The changes in the physicochemical proxies could have been responsible for the changes in the bacteria community in the "bottom ice" and "surface water". Otherwise, the different physiological characteristics of the planktonic bacteria phyla caused the different responses to the changes in the contents of the nutrient elements and physicochemical proxies in the frozen lake. For example, the major bacterioplankton phyla were mainly influenced by the changes in total phosphorus and dissolved total phosphorus in the "bottom ice" and by the changes in dissolved inorganic phosphorus and ammonia nitrogen in the "surface water". The results will provide basic data to analyze the lake ecological environment in Northern China.