A salamander's top down effect on fungal communities in a detritivore ecosystem.

The soil decomposer community is a primary driver of carbon cycling in forest ecosystems. Understanding the processes that structure this community is critical to our understanding of the global carbon cycle. In North American forests, soil fungal communities are regulated by grazing soil invertebrates, which are in turn controlled by the predatory red-backed salamander (Plethodon cinereus). The presence of these soil invertebrate taxa is known to exert direct top-down control via selective grazing on saprotrophic fungi, with direct consequences for biogeochemical cycling in soil. We investigated whether the removal of P. cinereus would relieve top-down control on decomposer fungal communities in a tri-trophic mesocosm study. Fungal communities were characterized using metabarcoding and high-throughput DNA sequencing. The β-diversity of fungal communities differed between salamander presence and absence treatments with a strong effect on saprotrophic fungal communities. We concluded that P. cinereus, a mesopredator in the detritivore food chain, exerts a prominent control on the composition and functional diversity of fungal communities in soil through a multi-trophic top-down process. Given their capacity to govern the compositions of soil invertebrates, the activity of these amphibians may be important for regulating ecosystem function and nutrient cycling in temperate forest systems.