The Chernobyl Exclusion Zone soil microbiome across radiation, soil quality and wildfire burn gradients

The soil microbiome of the Red Forest region of the Chernobyl Exclusion Zone was characterised along gradients of radiation contamination, recent forest fire extent and different land-use histories. Sites with previous history of conifer plantation (planted sites) were drier, with lower grass and herbaceous plant cover and generally higher radiation contamination than sites that were never planted with conifers (unplanted sites). Absorbed radiation dose rates to grass showed statistically significant correlations with shifts in microbial community structure in unplanted sites, while bacterial and tree dose rates generally showed non-significant correlations. The harsher ecological conditions in planted soils were associated with an enrichment of bacteria linked with stress-tolerator traits, a weaker microbial response to fire, less dense association networks with a greater proportion of negative associations. The more favourable conditions in unplanted sites were associated with a greater proportion of habitat-filtering associations and an enrichment of microorganisms with ruderal traits. Evidence was also found for guilds of closely-related, positively-interacting taxa in planted sites, which may be linked with microbial survival strategies in the harsher soil ecological conditions.