[Water Quality and Bacterial Population Driving Mechanism of Algae Vertical Succession in Stratified Reservoir].

Abstract

Phytoplankton and bacteria are important components of the aquatic food web, and play a critical role in substance circulation and energy exchange in freshwater ecosystems. The succession of algae is closely related to the metabolism and structural succession of bacterial populations in the water column. Thus, in this study, the vertical succession characteristics of phytoplankton and bacteria community structure and their coupling with water quality were investigated during an algal bloom in the Lijiahe Reservoir using high-throughput DNA sequencing and Biolog technologies. The results showed that the Lijiahe Reservoir was in the thermal stratification stage in August, and the pH, dissolved oxygen, and NH4+-N of the water column gradually decreased with depth (P<0.001). Algal cell concentration and chlorophyll a exhibited a simultaneous trend (P<0.001), and the maximum values in the surface layer were 3363.33×104 cells·L-1 and 7.03 μg·L-1, respectively. The algal community structure was dominated by Microcystis at water depths of 0 m and 3 m, and at 6 m water depth, Cyclotella replaced Microcystis as the most dominant algae, with a relative abundance of 57.28%. Biolog analysis indicated that the outbreak of Microcystis had a significant impact on bacterial metabolic activity and its relative abundance, but the diversity of bacterial population metabolic activity varied less. A total of 1420 operational taxonomic units were found by high-throughput sequencing, belonging to 10 bacterial phyla. Of these, Actinobacteria and Proteobacteria dominated in all water layers, and their relative abundances were more than 50%. The relative abundance of Chlorobi and Planctomycetes varied significantly with water depth, reaching their maxima at a depth of 6 m with values of 10.29% and 6.78%, respectively, which were both negatively correlated with algal density (P<0.05). Firmicutes and Gemmatimonadetes were positively correlated with algal density (P<0.05). A heat map fingerprint showed that the vertical distribution of the bacterial community structure of the Lijiahe Reservoir varied significantly, and with the increase in water depth, the bacterial community was more uniformly distributed and tended to diversify. Redundancy analysis (RDA) showed that the vertical distribution of the bacterial and algal community structure was regulated by different water qualities, and the difference was significant. This study investigated the coupling mechanism of algal and bacterial communities during the algal bloom in the Lijiahe Reservoir, and the results provided a scientific basis for the investigation of the molecular microecological driving mechanism of water-source algal blooms.