Indirect effects of trophic interactions govern carbon circulation in two beech forest soil ecosystems

1. Forests soils harbour a vast array of organisms that govern the processing of organic matter. Through their trophic interactions, they give rise to carbon flows that sustain soil ecosystem functioning. Understanding how soil food webs shape carbon flows may enhance our knowledge about the role of biodiversity on soil processes. 2. In this work, we assembled trophic networks representing soil food webs of two beech forests during spring and autumn, and compiled mass-balanced models quantifying carbon flows between their components. These models were investigated using network analysis to identify the role of the components on carbon flow, cycling and functional trophic relationships. Moreover, we explored how the structure of carbon exchanges promotes efficiency and stability. 3. Results indicate the importance of indirect interactions. Most trophic groups exhibit a diffuse dependency on all the compartments for their carbon requirement although certain groups such as Collembola play the role of hubs in distributing carbon. Indirect interactions often reverse the impacts of direct trophic relationships being antagonistic to the direction of change predicted based on predator-prey interactions. The high incidence of generalist feeding habits increases the redundancy of energy channels thereby making such food webs more resilient against perturbations but at the expense of carbon transfer efficiency. 4. Although differences can be observed across sites and periods, food web structure rather than environmental variability seems to be the main factor responsible for patterns of carbon flows in the two beech forests.