Soil fauna promote litter decomposition but do not alter the relationship between leaf economics spectrum and litter decomposability

Abstract

The leaf economics spectrum (LES) describes co-variation in leaf functional traits relevant to carbon and nutrient economics across plant species. It has been proposed that LES can be a useful predictor of litter decomposability, thereby influencing ecosystem carbon and nutrient cycling. However, the role of soil fauna in mediating the LES-decomposability relationship is largely unexplored. We evaluated leaf litter decomposability of 21 co-occurring tree species in a subtropical forest in China. We used litterbags with different mesh sizes to control litter accessibility to meso- and macrofauna. We quantified 9 leaf functional traits and 12 litter traits, and investigated how these traits were related to the losses of litter mass, carbon and nitrogen under different fauna treatments. Litter mass loss varied from 32.3 to 80.6% after 400 days of decomposition in the field. Meso- and macrofauna presence increased on average litter mass loss by 8.4%, carbon loss by 11% and nitrogen loss by 14.4%. Litter nutrient contents and stoichiometry generally had no significant effect on decomposition rates. Instead, structure-related traits such as toughness, lignin and labile compounds were generally strongly related to decomposition rates, suggesting that decomposition processes are strongly limited by energy availability. We found significant linear relationships between LES and litter mass or carbon loss, but not nitrogen loss. However, meso- and macrofauna presence did not significantly alter the regression slopes of these relationships, suggesting that meso- and macrofauna exert similar effects on decomposition of litter originating from tree species characterized by different life strategies. This study advances our understanding of the soil fauna in driving litter decomposition in subtropical forests.