Differential effects of moisture on surface versus mineral soil microbial communities in the High-Arctic

Abstract

Microorganisms play key roles in nutrient/carbon cycling and greenhouse gas fluxes in High-Arctic soils. However, the influence of soil conditions on tundra microbiomes remains poorly understood. Using high-throughput sequencing, we studied bacterial, fungal and micro-eukaryotic communities in surface soil-biocrust matrices and the underlying mineral soil along two environmental gradients in Svalbard. Both layers harboured highly different communities. Gravimetric water content and pH were the most important factors in explaining the variation in surface communities. Cyanobacteriota were the dominant phototrophs in wetter tundra soils, while Chlorophyta dominated drier ones. In mineral soils, soil texture explained community structure for all three groups, together with carbon-content and carbon: nitrogen-ratio for micro-eukaryotes and bacteria. Chloroflexota and Spirotrichea dominated mineral soils with high clay content, Actinobacteriota positively correlated with sand content. The effects of soil texture and water content were also reflected in co-occurrence networks. Surface communities split into two network clusters linked to either drier or wetter tundra. The mineral soil network was much less coherent, and clustering was related to soil texture. Our findings revealed the important interplay between soil layer, toposequence and soil microbiome in the High-Arctic. As precipitation patterns shift, the impact of topography on tundra microbial communities is likely to intensify.