Relative Importance of Climate, Soil and Plant Functional Traits During the Early Decomposition Stage of Standardized Litter

Climatic factors have long been considered predominant in controlling decomposition rates at large spatial scales. However, recent research suggests that edaphic factors and plant functional traits may play a more important role than previously expected. In this study, we investigated how biotic and abiotic factors interacted with litter quality by analyzing decomposition rates for two forms of standardized litter substitutes: green tea (high-quality litter) and red tea (low-quality litter). We placed 1188 teabags at two different positions (forest floor and 8 cm deep) across 99 forest sites in France and measured 46 potential drivers at each site. We found that high-quality litter decomposition was strongly related to climatic factors, whereas low-quality litter decomposition was strongly related to edaphic factors and the identity of the dominant tree species in the stand. This indicates that the relative importance of climate, soil and plant functional traits in the litter decomposition process depends on litter quality, which was the predominant factor controlling decomposition rate in this experiment. We also found that burying litter increased decomposition rates, and that this effect was more important for green tea in drier environments. This suggests that changes in position (surface vs. buried) at the plot scale may be as important as the role of macroclimate on decomposition rates because of varying water availability along the soil profile. Acknowledging that the effect of climate on decomposition depends on litter quality and that the macroclimate is not necessarily the predominant factor at large spatial scales is the first step toward identifying the factors regulating decomposition rates from the local scale to the global scale.