Different predictors determining litter decomposition rate in functional groups of the tree plantations in a common garden

This study shows that functional grouping of the species based on nitrogen fixing ability along with initial leaf litter C/P, C/N, P and N could help us predicting leaf litter decomposition rate. Grouping species into functional groups is a good approach to understanding exotic plants impacts on ecosystem functioning in their new environment. One key plant trait that has large ecosystem-level consequences is the ability of plants to fix atmospheric nitrogen into plant available forms. Most previous studies have reported faster leaf litter decomposition rates of nitrogen fixing than non-nitrogen-fixing species, supporting the separation of these as functional groups. Here, we present a multispecies monitoring of litter decomposability of seven tree species in a 1 year decomposition experiment in outdoor litter bed common garden experiment in river floodplain in South Western Iran. We tested within- and between-functional-groups for rates of leaf litter decomposition and nutrient dynamics. Our results highlight that nitrogen-fixing trees and non-nitrogen-fixing trees can be distinguished based on specific leaf area and leaf litter traits. The interesting results were that the leaf litter decomposition rates of the two functional groups were related to different initial leaf litter traits. Leaf litter decomposition rates of nitrogen-fixing trees were related to initial leaf litter C/P, C/N, N, P and Ca, while leaf litter decomposition rates of non-nitrogen-fixing trees were only related to initial leaf litter Ca. Whereas specific leaf area was the best predictor of leaf litter decomposition rates among all the species. Therefore, our results revealed that both initial leaf litter traits and functional groups were predicting leaf litter decomposition rates.