Linking resource and consumer diversity to ecosystem function in a detritus-based watershed
Kominoski, John Stephen
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Global species declines have prompted research exploring the relationship between biodiversity and ecosystem function. Earlier studies focused on terrestrial plant species richness effects on primary productivity. More recently, attention has focused on effects of leaf litter species diversity on decomposition in terrestrial and aquatic ecosystems. Using a full-factorial design of litter from four dominant riparian tree species, we tested for effects of nonrandom species loss on breakdown dynamics (litter mass loss, litter chemistry, microbes and invertebrates) in a detritus-based stream and compared results with data from a riparian study. Data were analyzed using statistical analyses that tested for additive effects of individual litter species presence/absence and nonadditive effects of species richness and species composition. We found nonadditive effects of litter species diversity on litter breakdown rates that were explained by litter species richness and composition. We observed nonadditive effects of litter species diversity on litter nutrients and secondary compounds and additive effects on structural compounds. Nonadditive effects of litter species diversity on bacterial and fungal biomass were seen during early stages of breakdown, and additive effects on microbes during intermediate and later stages of breakdown were explained by the presence/absence of high- and low-quality litter species. We found both nonadditive effects of litter species diversity and additive effects of species identity on macroinvertebrates that varied with time and litter chemistry. Mixing higher-quality litter with low-quality litter resulted in shifts in microbial community diversity and altered processing dynamics of individual litter species. Using an information-theoretic approach to compare stream and riparian datasets, we found that although litter species traits persisted during processing in both ecosystems, the relative importance of specific traits and species composition on litter processing varied between terrestrial and aquatic ecosystems. Inputs of terrestrially derived litter to stream ecosystems can be influenced by invasive plant pests. The hemlock woolly adelgid appeared to drive seasonal hemlock and carcass inputs to our study stream. Our results suggest that predicted changes in tree species composition in riparian forests will likely alter invertebrate and microbial communities that interact with litter quality and diversity to differentially affect detrital processing in terrestrial and aquatic ecosystems.