Functional Traits and Species Identity Drive Decomposition Along a Successional Gradient in Upper Andean Tropical Forests

Abstract

Leaf litter decomposition constitutes one of the most vital processes for maintaining productivity and carbon release in ecosystems. However, this remains one of the least understood processes in upper Andean tropical forests (UATF), a highly diverse ecoregion that has undergone extensive transformation over the centuries. In this study, we aimed to determine the relationships between decomposition rates of leaf litter, leaf functional traits, and microclimatic conditions along a successional gradient of UATF. We also tested the “after-life effect” by analyzing changes between green and senescent leaves. We performed a fully reciprocal translocation experiment with 15 representative species of UATF in a set of 14 permanent plots by using 2520 litterbags distributed across 42 experimental units (three litterbeds per plot), over 1.5 years, with four harvesting times (3, 6, 12, and 18 months). Chemical and physical traits were measured in green and senescent leaves to identify the best predictors of decomposition and to analyze the “after-life effect.” We found that functional traits and species identity drive litter decomposition in UATF, rather than succession and microclimatic conditions of soil moisture and temperature. The relative importance of traits was prevalent in all stages of decay, despite being stronger in the early phases. Although we found an “after-life effect” of green leaves in decomposition, changes in chemical composition from green to senescent leaves indicated substantial nitrogen resorption, which is a limiting resource in tropical montane forests. With the increasing landscape transformation in UATF, changes in plant species composition could have profound impacts by altering decomposition rates, nutrient cycling, and global carbon storage.