Interaction of soil fauna and plant litter composition on decomposition processes across the litter-soil interface

Plant chemical composition and the soil community are known to influence litter and soil organic matter decomposition. Although these two factors are likely to interact, their mechanisms and outcomes of interaction are not well understood. Studies of their interactive effects are rare and usually focus on carbon dynamics of litter, while nutrient dynamics in the underlying soil have been ignored. Further, 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 spanning wide ranges of multiple quality parameters 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. We restricted the access of larger soil animals to the soils underlying these litters to investigate the role of soil fauna (meso, macro) in determining the effect of surface-litter chemical composition on nitrogen mineralization and on the microfood web in mineral soils. Over six months we assessed litter mass and nitrogen loss, nitrogen mineralization rates in the soil, and litter and soil microbes and micro- and mesofauna. We found evidence that the structure of the soil community can alter the effect of surface litter chemical composition on nitrogen dynamics in the mineral soil, contribute to evidence demonstrating that soil fauna shape plant litter effects on ecosystem function. Decomposer communities and N dynamics did not respond similarly to the litter mixture across the litter-soil interface, 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.