Disentangling terrestrial microbial community composition in the Sør Rondane Mountains, East Antarctica

The sparse ice-free regions of Antarctica are the coldest deserts on Earth. Yet, ice-free soils harbor substantial microbial communities that can vary significantly in response to environmental and micro-climatic conditions. The factors responsible for driving the microbial diversity and community structure in inland nunataks of East Antarctica are still poorly understood. Within the MICROBIAN project, two sampling campaigns took place in the Sør Rondane Mountains during the austral summers of 2018 and 2019, resulting in more than 100 samples ranging from different types of barren bedrock to well-developed biological soil crusts. Bacterial and eukaryotic diversity was assessed by amplicon sequencing targeting the V1-V3 variable region of the 16S rRNA gene and the V4 region of the 18S rRNA gene with general bacterial and eukaryotic primers using the Illumina MiSeq v3 platform. To investigate the responses of these communities to soil driven geochemical variables (such as pH, TN, TOC, NH4-N, etc.) across the sampled bedrock types (gneiss, granite, marble and moraine) we coupled a Spearman co-occurrence network of ASVs (ρ > 0.7 and p-value < 0.01) to random forest variable ranking and correlations with Spearman and Pearson statistics. A total of 13 clusters (modules) were observed, of which 8 gathered 82% of the ASVs and 97% of the reads in the network. Modules of ASVs that mostly occurred in granitic soils were dominated by filamentous Cyanobacteria and correlated well with increasing NH4-N concentrations while unicellular Cyanobacteria dominated modules occurring in marble samples which correlated well with increasing pH values. One module occurring in gneiss soils was dominated by Proteobacteria and correlated with increasing TOC concentrations, whereas Actinobacteria dominated modules occurring in moraine samples which correlated with increasing TN concentrations. Chlorophyta was the most ubiquitous eukaryotic Phylum, and Metazoa were surprisingly found in the dry and oligotrophic moraine soils as well