Grass encroachment in heathland and microbial community structure

In many ecosystems, the identity of the dominant plant is changing because of global change. If the new dominant species has different litter and root traits than the one it replaces, it is likely to have an influence on soil microbial communities and the functions they perform. We established a 13-plot field observatory spanning across a 0-100% gradient of grasscover percentage. In each plot, we characterized amongst others, plant, fungal and bacterial communities, using metabarcoding. Our results showed that microbial taxonomic and functional diversities are not affected by grass colonization. Microbial communities were also similar at high phylogenetic level, including for ericoid mycorrhizas and typical oligo- and copiotrophic species. At a finerphylogenetic level, some abundant extremophilic OTUs ( e.g Acidothermus bacteria) were progressively replaced by fungal black yeasts. Functional response of microbial communities was more obvious. The C mineralization potential significantly increased across the grass gradient.