Global pattern in terrestrial leaf litter decomposition: The effects of climate, litter chemistry, life form, growth form and mycorrhizal association

Leaf litter decomposition plays an important role in nutrient and carbon cycling in terrestrial ecosystems. However, at a global scale, the effects of climate, initial litter chemistry, and different plant functional types on litter decomposition are not fully understood. Additionally, it remains unclear whether the effects of litter chemistry on leaf litter decomposition are consistent with responses observed at local scales. Here, 1585 observations of leaf litter decomposition encompassing 861 species from 298 field studies were synthesized to investigate the effects of climate, litter initial chemistry, and various plant groups on decomposition rates. The results demonstrate that at a global scale, leaf litter decomposition rates increased with mean annual temperature (MAT), mean annual precipitation (MAP), initial litter concentrations of nitrogen (N), phosphorus (P), and magnesium (Mg), but decreased with initial lignin concentrations. Moreover, except for initial leaf litter Mg concentrations, the influence of initial leaf litter chemistry characteristics on decomposition rates were consistent at global and local scales. In woody plants, leaf litters from deciduous, broadleaf, and arbuscular mycorrhizal (AM) species exhibited faster decomposition rates than from evergreen, coniferous, and ectomycorrhizal (ECM) species leaf litters, respectively. In herbaceous plants, the leaf litter of forbs had faster decomposition rates than graminoid and leguminous plants. For all plants, leaf litter decomposition is primarily controlled by MAP and MAT globally, while for woody and herbaceous plants, leaf litter decomposition is primarily controlled by initial leaf N and P concentrations, respectively. These results indicated that various functional groups of plants play a crucial role in understanding the decomposition of leaf litter. Moreover, when investigating the effect of leaf litter initial chemistry on its decomposition, it is almost unnecessary to consider effects at different scales.