Leaf-litter microbial communities in boreal streams linked to forest and wetland sources of dissolved organic carbon

Leaf-litter microbial activity is influenced by several stream characteristics that may be affected by alterations in watershed condition. However, there have been few studies and little direct evidence that leaf-litter microbial communities are affected by disturbance-induced watershed condition, particularly in boreal streams. To test this linkage, we compare the associations of stream physical-chemical characteristics with landscape features (e.g., percent wetlands, roads, riparian woody stem diversity), and leaf-litter microbial activity and structure in streams across varying disturbance-induced watershed conditions. Our findings suggest that the increased stream water conductivity associated with roads can have a negative impact on leaf-litter microbial extracellular enzyme activity associated with a decrease in the abundance of Betaproteobacteria. Wetlands and forests in contrast are important providers of dissolved organic carbon that stimulates the microbial, and in particular fungal, cycling of energy and nutrients. We present a novel and in-depth perspective of leaf-litter microbial communities as a critical link to our understanding and management of the influences of watershed condition on aquatic ecosystems.