Restoring aboveground trophic diversity contributes to belowground microbial diversity in drylands

Trophic cascades in ecology are vital for restoration and conservation management of ecosystems. However, their contribution to belowground microbial diversity remains poorly understood. We examined the microbial contributions of aboveground organisms, at different trophic levels to the soil microbiome, within a rewilded arid environment. We selected five trophic organisms which interacted with or inhabited the soil: Acacia ligulata rhizosphere (primary producer), ants (primary consumer), two omnivorous mammal species (secondary consumers), a carnivorous mammal species (tertiary consumer), and collected soil from the rewilding area and a control (not rewilded) area. Next generation sequencing of 16S and 18S rRNA genes was used to identify bacteria, fungi and micro-eukaryotes, significantly different between the rewilded soil and control soil, and also varying in presence and composition among the five trophic organisms. We identified 49 bacterial taxa, significantly different in abundance in the rewilded soil, compared to the control soil. These taxa also occurred in one of the secondary consumers and the tertiary consumer. Fungal and micro-eukaryotic sequences were very low in soil samples, with no differentiation between rewilded and control areas. We found potential for top-down influences on the soil from rewilding, with the rewilded mammals hosting different functional groups of consumer protists and arthropod pathogens. Rewilded secondary consumers hosted saprotrophic and ectomycorrhizal fungi, and the tertiary consumer hosted dominant generalist fungi. Our results identified changes in composition of key dryland soil taxa from rewilding, through direct and indirect interactions with the soil, underlining the value of trophic rewilding to improve restoration success of soil in drylands.