Functional shift from symbiotic to saprotrophic fungal community composition in soil under deadwood
Deadwood is an important component in forest ecosystems that may increase organic carbon and microbial biomass in soil. However, the response of the fungal community and respective ecological functions in soil under deadwood has remained largely unclear. In this study, we assessed the effect of logs of thirteen tree species (nine broad-leaved and four coniferous) on the fungal diversity and community composition in underlying mineral soils in 30 forest plots across three German regions with distinct soil properties. Mineral soil was collected beneath the logs after 8 years of decay and from the neighbouring uncovered soil unaffected by the deadwood. The soil fungal communities were accessed by metabarcoding (Illumina MiSeq) of ITS rRNA gene amplicons from DNA extracts. In addition, fine root traits were determined in soil under logs of Fagus and Picea and in uncovered soil. Soil fungal community composition under logs differed according to region, soil pH, forest type, management type, plot and deadwood presence, while no differences were observed for the deadwood species. Log decomposition shaped the fungal community composition by increasing the abundance of saprotrophic fungi and decreasing symbiotrophic fungi. The increase of saprotrophic fungi was negatively correlated with fine root biomass, indicating that logs promote the spread of saprotrophic fungi in the soil. Most of the dominant basidiomycetes in soil under logs were assigned to typical deadwood decomposers, indicating that these fungi can grow from logs into the topsoil and vice versa. Logs further increased the fungal diversity in underlying soil. Our results suggest that deadwood is an important driver of the fungal community composition and diversity in forest soils.