Co-occurrence networks show response of microbial communities to warming in tundra soils

The arctic tundra is experiencing dramatic changes due to global warming. The directional changes in vegetation cover.is expected to impact the soil microbial communities, with consequences for overall ecosystem functioning. Samples were collected from 19 warming experiments within the International Tundra Experiment (ITEX) across 13 sites each with 4 control plots and 4 open-top chambers. We used metabarcoding of the ITS region and 16S rRNA gene to describe the fungal and prokaryotic communities and quantified the genes involved in nitrogen cycling. Our aim was to investigate if the co-occurrence networks were modified by warming by comparing the topologies of the “small-world” networks, typical of microbial systems. The fungal network was reorganized in the warming experiment, with a strong increase of the length of the paths between nodes and a modification of most of the modules. Those modules, indicating fungal consortia sharing the same ecological niche, were related individually to sites and vegetation, suggesting a site-dependent response to experimental warming. For prokaryotes, the modules were preserved between the control and the treatment and harbored similar relationships with soil nutrients and N-cycling genes, but a turnover of putative keystone species was observed between conditions. The negative co-occurrences between prokaryotic members was denser in the warming treatment compared to the control. This expansion of negative links is indicative of disturbance as they typically increase stability of complex networks under perturbation. In conclusion, warming resulted in disturbances on the interactions within the microbial communities, which potentially impact nutrient cycling and above- and belowground interactions.