The influence of litter composition across the litter-soil interface on mass loss, nitrogen dynamics and the decomposer community

Many studies have investigated the influence of plant litter species composition on decomposition, but results have been context-dependent. Litter and soil are considered to constitute a decomposition continuum, but whether litter and soil ecosystems respond to litter identity and mixing in the same manner is unsure. In a field experiment utilizing 5 litter species and their mixture, we investigated whether the effects of litter identity and mixing on mass loss, nutrient dynamics, and decomposer communities are consistent across the litter-soil interface. In monoculture, mass loss and nitrogen (N) dynamics in the litter layer corresponded to the underlying soil N availability, demonstrating the continuum of resources from litter to soil. Litter microbial biomass and mesofauna abundance tended to be greater on litter with a faster decay rate and greater N release. However, soil decomposer abundance and diversity were not greater with higher soil N, causing litter and soil communities to respond differently to litter identity. Non-additive mass loss and N dynamics were observed after 6 months, and were correlated with non-additive litter microbial community composition and litter mesofauna communities, but all other aspects of the litter community and all measures of the soil community were additive. Decomposer communities and N dynamics did not respond similarly to the litter mixture across the litter-soil interface. This study is one of the few to comprehensively examine how a litter mixture influences decomposition dynamics and communities across the soil-litter interface, including multiple taxa and trophic levels. Our results demonstrate that processes associated with decomposition are decoupled for litter and soil, particularly in that litter showed non-additivity in mass loss, N release and decomposer community, but soil responses were largely additive.