Effects of leaf litter species richness and composition on nutrient turnover and decomposer biota

Abundant research has examined the effects of species diversity on decomposition and its related properties. Increasingly, studies suggest that species composition, rather than diversity, has a greater impact on decomposition processes. However, the results of most of these studies are not easily interpreted, and often appear idiosyncratic, due to the inability to decompose statistically the effects of “diversity” into its component effects of species richness and species composition. Using a fully factorial manipulation of tree leaf litter species diversity, we explored the effects of both species richness and composition on litter decomposition. We selected four leaf litter species covering a range of resource qualities and decay rates for a 3-year litterbag decomposition study at Coweeta LTER in the southern Appalachians. We explored the additive and non-additive effects of richness and composition on decomposition, measured through leaf litter chemical quality, decomposer fauna, and decay rate. Results demonstrated that species composition, rather than richness, had both additive and nonadditive effects on decomposition, particularly affecting litter primary chemistry, suggesting significant impacts of species loss on nutrient dynamics in leaf litter.