Steering the soil microbiome by repeated litter addition

Microbial communities drive plant litter breakdown. Litters originating from different plant species are often associated with specialised microbiomes that accelerate the breakdown of that litter, known as home-field advantage. Yet, how and how fast microbial communities specialise towards litter inputs is not known. Here we study effects of repeated litter additions on soil microbial community structure and functioning. We set up a 9-month, full-factorial, reciprocal litter transplant experiment with soils and litters from six plant species (three grasses and three trees). We measured fungal and bacterial community composition, litter mass loss and home-field effects. We found that repeated litter additions resulted in convergence in fungal community composition driven by litter functional group (trees vs. grasses). Grasses enriched Sordariomycetes, while Tremellomycetes, Eurotiomycetes and Leotiomycetes were favoured by tree litter. Bacterial community composition, litter mass loss and home-field effects were not affected by litter incubation, but there was a relationship between fungal community composition and mass loss. We conclude that repeated litter incubations can result in directional shifts in fungal community composition, while 9 months of litter addition did not change bacterial community composition and the functioning and specialisation of microbial communities. Testing further how repeated litter inputs affect microbial functioning is essential for steering decomposer communities for optimal soil carbon and nutrient cycling.