Temperate trees locally engineer decomposition and litter-bound microbiomes through differential litter deposits and species-specific soil conditioning.

Leaf decomposition varies widely across temperate forests, shaped by factors like litter quality, climate, soil properties, and decomposers, but forest heterogeneity may mask local tree influences on decomposition and litter-associated microbiomes. We used a 24-yr-old common garden forest to quantify local soil conditioning impacts on decomposition and litter microbiology. We introduced leaf litter bags from 10 tree species (5 arbuscular mycorrhizal; 5 ectomycorrhizal) to soil plots conditioned by all 10 species in a full-factorial design. After 6 months, we assessed litter mass loss, C/N content, and bacterial and fungal composition. We hypothesized that (1) decomposition and litter-associated microbiome composition would be primarily shaped by the mycorrhizal type of litter-producing trees, but (2) modified significantly by underlying soil, based on mycorrhizal type of the conditioning trees. Decomposition and, to a lesser extent, litter-associated microbiome composition, were primarily influenced by the mycorrhizal type of litter-producing trees. Interestingly, however, underlying soils had a significant secondary influence, driven mainly by tree species, not mycorrhizal type. This secondary influence was strongest under trees from the Pinaceae. Temperate trees can locally influence underlying soil to alter decomposition and litter-associated microbiology. Understanding the strength of this effect will help predict biogeochemical responses to forest compositional change.