Daisy Lake Shotgun

Organic matter (OM) derived from terrestrial ecosystems influences both the food webs and biogeochemical cycles of lakes. The boreal ecozone holds an estimated 60% of the world's fresh water, but lakes in this region tend to be nutrient-poor and less productive, making them especially reliant on carbon subsidies from riparian litterfall. The availability of these carbon subsidies for aquatic food webs depends on microbial communities, but little is known about how the taxonomic and functional diversity of heterotrophic bacteria might influence the rate at which this OM is decomposed in natural systems. Drawing upon biodiversity-ecosystem functioning theory, we predicted that decomposition rates, indicative of both food web production and whole-lake carbon cycling, increase with the taxonomic and functional diversity of bacterial communities. We characterized both bacterial community composition and microbial functional traits in nearshore sediments from 8 catchments along a gradient of terrestrial OM inputs using next-generation sequencing (16S rRNA amplicon sequencing and shotgun metagenomics). We found that both species richness and composition explained variation in rates of OM decomposition among sites. Differences in species composition were largely driven by 17 bacterial families, with abundances of Acidobacteria, Firmicutes and Actinobacteria changing along OM gradients. Ongoing shotgun sequencing will provide more detailed information on the functional traits present in lake sediments. This study highlights the role of microbial communities in the transfer of resources from terrestrial ecosystems, and improves our understanding of how catchment disturbances affect boreal aquatic ecosystems.