Reintroduction of threatened digging mammals influences soil microbial communities differently along a rainfall gradient

Ecosystem engineers influence co-existing species indirectly, through their modification of habitat conditions, so the loss of these species may have broad consequences for ecosystems globally. Digging mammals alter soil via soil turnover, habitat modification and mycophagy. However, we have a limited understanding of their impacts in different environments. In a continent-scale study spanning 3000 km across southern Australia, we asked whether reintroductions of native digging mammals affect soil microbial communities in the soil matrix outside of their diggings, and if those impacts depend on the environmental context? We used high through-put sequencing analysis of bacterial and fungal environmental DNA to measure soil microbial diversity and community structure inside and outside digging mammal reintroduction areas at five reserves along a rainfall gradient from 166 to 877 mm per year, covering arid, semi-arid and temperate systems. Bacterial observed richness was not different inside and outside of the reserves; in contrast, fungal richness was higher in reserves, but only in arid and semi-arid environments. Fungal saprotrophs were more abundant in reserves: the mixing of soil layers mediated by digging mammals might therefore enhance decomposition. However, crust-forming microbes and ectomycorrhizal fungi were lower in abundance inside reserves, likely due to the disturbance and the altered soil nutrients that resulted from digging activity. Impacts of digging mammals varied among ecosystems which highlights the need for managers to consider the ecological context of reintroductions of ecosystem engineers when restoring for ecological functions.