Time-varying associations between absorptive fine roots and leaf litter decomposition across 23 plant species

Abstract

Litter decomposition is the first step for soil organic matter (SOM) formation. By transferring carbon, nutrients and energy from plant to soil, litter decomposition maintains soil fertility and soil health in terrestrial ecosystems. The dominant factors regulating leaf litter and fine root decomposition rates affect how plant biomass is decomposed into new products (such as CO2), contribution to the basic scientific research and beyond, into the realms of land management and global change policy. Litter chemistry, such as the high nitrogen (N) concentration in recently senesced tissues, is related to higher rates of leaf litter decomposition. However, it is unclear whether long-term decomposition of fine roots is coordinated with leaf litter decomposition, based on the initial chemical traits of these tissues. Here we followed the decomposition of leaf litter and absorptive fine roots (the distal three root-branch orders) across 23 species over five years in a temperate grassland. We found that decomposition rates of absorptive fine roots were significantly correlated with those of leaf litter in the initial stage, across grassland species. However, this tight coordination between leaf litter and fine root decomposition diverged with time. Absence of correlation between leaf and fine root decomposition in later stages of decomposition arose partly because of dissimilar tissue chemistry of absorptive fine roots and leaf litter, and partly because of the different driving factors for decomposition of absorptive fine roots and leaf litter. Our results suggest that the chemical traits could predict the fate of fine roots vs. leaf litter in the early stage of decomposition but may be not valid during the later decomposition stage or for explaining the trajectory of long-term decomposition, when the accumulated recalcitrant compounds were more influential in the decomposition process.