Temporal variation in glacier snowpack bacterial communities mediated by nitrogen

Abstract. Global warming accelerates glacier melt, releasing stored carbon and nitrogen, which fertilize downstream ecosystems. Diverse and active microbial communities mediate biogeochemical cycles in snow and are vital to the glacial ecosystem. However, little is known about their temporal changing pattern and the environmental and biotic determinants in snowpacks. Here, we investigated the bacterial community in the surface and subsurface snow (depth at 0–15 and 15–30 cm, respectively) during a nine-day period in the Dunde Glacier of the Tibetan Plateau, based on Illumina MiSeq of 16S rRNA gene sequences. Our results revealed dynamic bacterial communities in both surface and surface snow, and nitrogen is the key determinant of bacterial diversity, composition, community structure, and biotic interactions. Nitrate and ammonium concentration increased and decreased in the surface and subsurface snow over time, therefore indicating accumulation and consumption processes, respectively. This is also evidenced by the dominance of organisms predicted to carry nitrogen fixation and denitrification genes in the surface and subsurface layers, respectively. The nitrogen limitation and the apparent dominance of the denitrification in the subsurface snow suggest stronger environmental and biotic filtering than those in the surface snow. This was associated with lower bacterial diversity, more pronounced community temporal changes, and stronger biotic interactions than in the surface snow. Collectively, these findings significantly advanced our understanding of microbial community variations and bacterial interactions after snow deposition, and revealed the dynamics of nitrogen metabolism in Tibetan snow.