Disentangling effects of litter quality and biotic soil regulation on litter decomposition processes in forests of the northern hemisphere using a synthetic community approach

This PhD proposal aims at investigating the linkages between tree biodiversity and litter decomposition, a key ecosystem function affecting nutrient and carbon cycles. To do this, we use a synthetic community approach capitalizing on the unique geographical arboretum of Tervuren (B) that features the world’s major temperate and boreal forest communities. It allows testing the effect of composition, traits and biogeographical origin for an unprecedented range of tree communities, while controlling for climate and soil. The analysis of obtained data will explicitly account for non-linear threshold behavior. Focusing on the initial stages of leaf litter decomposition, we hypothesize that different tree communities result in contrasting decomposition rates through the supply of litter inputs of varying quality and quantity (direct effects), as well as through their impact on the decomposition environment (indirect effects). We first characterize the tree communities and their leaf litter inputs, using diversity metrics. In a second step, we assess the decomposition environment under the communities by characterizing the microclimate, topsoil properties, as well as microbes and detritivore communities. In a third step, we quantify the decomposition of both community-level leaf litters and reference litters, to separate between the direct and indirect effects of tree communities. Finally, we use non-linear structural equation modelling to disentangle the complex web of interactions among litter inputs, decomposition environment and decomposers. Motivated by the unanimously stimulating feedback on previous submission, this proposal was further improved by explicitly demonstrating the feasibility of the PhD in terms of sampling effort, and by controlling confounding soil factors with the added expertise of co-PI Karen Vancampenhout.