Microbial Communities and Biogeochemical Processes in High-Altitude Cascade Lakes of Central Caucasus (Lake Klukhor)
摘要
Microbial communities in the water column of high-altitude lakes of Central Caucasus (Lake Klukhor) were investigated in August, 2023. The data on microbial community composition and the rates of microbial biogeochemical processes were obtained. The lakes of the cascade (Big, Small, and East Klukhor) are located at the altitude of 2670–2980 m above sea level; they are low-mineral and oligotrophic, with similar hydrochemical composition, but varying in the water temperature and transparencey. Photosynthetic primary production was 5.3–8.0 µg C day–1, and the rate of dark CO2 assimilation was 0.5–1.2 µg C day–1. Total microbial abuncance varied from 70 to 150 × 103 cells mL–1. The dominant bacterial phyla in the water columns of oligotrophic Klukhorskoe lakes were Actinobacteriota, Bacteroidota, and Pseudomonadota, represented mainly by aerobic heterotrophs. Archaea constituted less than 1% of the community. Bacterial indicators of turbid and transparent waters of the studied lakes were revealed: aerobic gram-positive members of the family Ilumatobacteraceae, psychrophiles of the family Comamonadaceae (important components of the glacier microbiomes), and oligotrophs of the family Sphingomonadaceae, known to be resistant to solar radiation, including the ultraviolet one. The microalgal community of the water column included green microalgae, the Pinnularia diatoms, chyrsomonads, and cryptomonads. The microalgal composition of the three lakes varied noticeably. The cyanomicrobiome was less diverse in the transparent Lake Small Klukhor than in Lake Big Klukhor. The water column of the latter lake contained copepods Centropages sp. and Acanthodiaptomus denticornis, adapted to such extreme conditions of high-altitude environments as low temperature and high nultraviolet irradiation. The results of the work indicate that formation of new periglacial lakes losing connection to the glaciers due to their retreat lead to alteration in the structure of planktonic communities during transition from turbid glacial lakes to transparent ones. The composition of microbial communities of such lakes and its biogeochemical productivity may be indicators of local and large-scale climatic changes.