Plant diversity and local environmental conditions indirectly affect litter decomposition in a tropical forest

Abstract

One of the challenges in predicting the effects of biodiversity on ecosystem functioning is understanding the balance between the importance of various diversity components and variations in the environment. In mega-diverse tropical forests, these relationships between plant diversity and ecosystem processes, such as litter decomposition, are poorly explored. While the direct effects of plant diversity on litter decomposition are relatively well known, the indirect effects of diversity, and the local community and microenvironment have rarely been investigated. We evaluated the indirect effects of plant diversity on litter decomposition in a tropical forest. We assessed diversity using different components (plant species richness, functional composition, and functional diversity), evaluated the environmental gradient (soil attributes, topography and canopy cover) and related it to the dynamics of litter decomposition. A 230-day in situ experiment was performed in the southern areas of the Brazilian Atlantic forest using litterbags filled with standard substrate (to test the indirect effects) to evaluate the decomposition rates. In parallel, we also conducted a taxonomic and functional survey of the vegetation in the area of influence of the decomposition experiment. We demonstrated that there is an indirect effect of plant diversity, via taxonomic and functional diversities, on litter decomposition. The indirect effect is more pronounced at the beginning of the decomposition process, and the influences of different components of diversity and ecological mechanisms (niche complementarity, mass effect and selection effect) vary over time. Our study revealed the importance of not only small-scale variations in the biotic component but also those of soil in ecosystem functioning in a megadiverse forest. In this way, we have contributed to a better understanding of the determinants of the decomposition process, in addition to those suggested by classical theoretical models (i.e., climate, litter composition and decomposers).