Slow breakdown: Does microbial functional overlap drive non-additive litter decomposition?

In order to pursue a more comprehensive understanding of biodiversity impacts on litter decomposition we investigated how litter mixtures and microbial communities interact in two distinct ecosystems, mangroves and mixed conifer forests. Decomposition occurs very slowly in mixed conifer forests and extremely rapidly in mangroves, allowing for comparisons across a broad range of ecosystem rates. In both ecosystems, we determined not only that plant species decompose more rapidly in mixture than alone, but our data also suggest that the functional identity of litters in mixture drove these “synergisms.” Only nutrient poor and recalcitrant mixtures of litter yielded faster rates (up to 50%) of litter decomposition than would be predicted from their solitary rates, despite large differences in absolute decomposition rates between the two ecosystems. Further, microbial communities, as indicated by phospholipid fatty acid (PLFA) signatures, were distinct on different litter functional types. In ongoing experiments, we are examining how recalcitrant litter mixtures feed back to impact seedling performance and growth, which is especially important due to mangrove restoration efforts in coastal areas. Overall, this research can advance our understanding of the mechanistic underpinnings for biotic control of ecosystem function.