Root quality and decomposition environment, but not tree species richness, drive root decomposition in tropical forests

Background and aims Tropical forests contribute significantly to the global carbon cycle, yet the relative importance of tree diversity on key ecosystem processes such as root decomposition remains unknown. Methods We examined the influence of tree species richness on root decomposition over 485 days at two sites in Panama with contrasting soil fertility. Diversity effects on decomposition rates were calculated where 1) overstory tree species richness and composition matched that occurring inside root decomposition bags and 2) where roots of contrasting species richness decomposed under a common tree overstory. In addition, we tested 27 root traits to identify those that contribute to predict root decomposition in tropical forests. Results Tree species richness did not affect root decomposition rates, neither when species were manipulated within bags nor with varying tree overstory richness. Root carbon quality and micronutrient concentrations such as manganese explained 47 and 81 % of the variation in decomposition rates in the fertile and infertile site, respectively, demonstrating that the relative importance of traits was modulated by the soil environment. Conclusions Our results suggest that root decomposition in tropical forests is mediated by root functional composition and the soil environment rather than by species richness.