Local-scale variability in snow chemistry drives distinct microbial communities in Alpine seasonal snowpack

Abstract

Seasonal snowpack is a dynamic system that accumulates atmospherically transported particles, including dust and biological material such as microorganisms, from both local and long-distance sources. Here, we investigated the relationship between bacterial community composition and chemical properties of seasonal snowpack in mid-altitude valleys of the Swiss Alps. We characterised microbial community structure and diversity in surface snow and in 10–15 cm-deep snow across three adjacent valleys (elevations 1798–2578 m a.s.l.). Analysis of major ions and organic acids was used to identify key environmental factors influencing microbial community composition. While geographical location showed no clear influence on either the chemical composition or the bacterial community composition, bacterial community structure varied significantly with elevation. We identified significant differences between snow depths, with surface snow showing higher diversity than subsurface snow and exhibiting greater cross-site similarity. Surface snow contained twice as many bacterial genera in the core community as underlying snow, with nearly complete overlap. Total inorganic nitrogen and Ca2+ were key chemical variables associated with microbial community composition in the snowpack. Using Weighted Gene Co-expression Network Analysis (WGCNA), we identified modules of co-occurring bacterial taxa with distinct responses to these chemical gradients. Genera containing spore-forming taxa (Neobacillus, Niallia, Sporosarcina) were significantly associated with communities with higher nitrogen concentration, while Brevundimonas, Cryobacterium, and Polaromonas were associated with higher-calcium communities. The distinct patterns in chemistry and microbial community structure observed within just 10–15 cm reflect differences in atmospheric sources of deposited precipitation, with additional effects from post-depositional processes. This environmental filtering decreases local diversity while selecting different species based on initial community composition and local conditions. Understanding these bacterial-physicochemical relationships offers insights into how mountain ecosystems adapt to climate-driven changes in snow cover duration and atmospheric conditions.