Patterns and controlling factors of decomposition in distal shoot systems by branch order across 10 temperate tree species

Plant litter decomposition is a crucial pathway of the global carbon (C) cycle, and controls the net primary productivity in terrestrial ecosystems. Our understanding of litter decomposition is primarily based on decay patterns observed for leaf litter tissues. The distal shoot systems (leaves and the first few orders of twigs) vary vastly in function and tissue chemistry and both decomposition patterns and controlling factors of these multi-type litter complexes are poorly understood. We followed decomposition of leaf litter and the first three orders of twigs across 10 temperate tree species over 2 years in Northeast China. Eight species showed slower decomposition rates in twigs than leaf litter, and almost all species showed that decomposition rates decrease from first- to third-order twigs. The decomposition of twigs and leaf litter in 10 tree species were not coordinated. Most importantly, in contrast to leaf litter, the variation in twigs decomposition cannot be predicted by the commonly used parameters like N contents, but is predicted by initial concentrations of Mg and cellulose plus lignin/P ratio in twig tissues. We conclude that there were significant differences in decomposition rates among the tree distal shoot systems. Leaf litter decomposition does not mirror twigs decomposition, and variation in their decomposition rates was driven by two different subset of litter traits, at least in the ten species we studied. Additionally, the heterogeneity within the tree distal shoot systems could lead to differences in their contribution to soil in term of carbon dynamics.