Effects of litter quality and quantity on chemical changes during eucalyptus litter decomposition in subtropical Australia

Abstract

Litter inputs are closely related to both forest productivity and nutrient cycling under climate change and local management. This study investigated the effect of litter inputs on litter decomposition, changes in litter chemistry and nitrogen (N) dynamics during eucalyptus leaf litter decomposition. Two parallel in situ litter decomposition experiments were conducted at two sites with high-quality (HQ) and low-quality (LQ) litters in a eucalyptus-dominated forest of southeast Queensland, Australia. At each site, leaf litters with either a single (SL) or double mass load (DL) of litter inputs were decomposed for 15 months. Litter mass loss, chemical composition and N content of decomposing litters were measured seasonally during the decomposition period. The chemical composition of the collected litters was determined by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The HQ litters decomposed faster than the LQ litter, with a decomposition constant of 0.53 and 0.33 y−1 at the HQ and LQ site, respectively. Litter addition rates had no effect on litter decomposition, changes in chemical composition and N content during decomposition regardless of differences in initial litter quality. The HQ and LQ litters showed the same pattern of chemical changes during decomposition, with an increase in alkyl C and a decrease in di-O-alkyl C and aryl C. The relative intensity of O-aryl C and carboxyl C converged, while the relative intensity of di-O-alkyl C and δ15N diverged as the decomposition progressed. N immobilization during decomposition depended on litter quality, with N consistently immobilized in LQ litters over the whole decomposition period. In subtropical eucalyptus-dominated forests, the dynamics of organic C and N during litter decomposition were resistant to the increased inputs of aboveground litters. Litter chemistry of different initial qualities converged at the early stages of decomposition, and the implications of chemical convergence on the formation and stabilization of soil organic matter need to be assessed in the future.