Microorganisms at the intersection of hydrology and CO 2 efflux in subalpine soils

Abstract

Subalpine forests are responsible for a substantial fraction of carbon (C) cycling in the western United States, with over 70% of the C sink activity taking place at elevations exceeding 750 meters. Soil microbial communities are key drivers of C cycling in these ecosystems, yet, factors that influence the composition of these communities and their activities across these heterogeneous subalpine landscapes are not well understood. Ten geographically distinct coniferous forest watersheds across western Montana were subjected to characterization of soil properties, carbon dioxide (CO 2) efflux, and community composition to determine the influence of heterogeneity in these watersheds on these properties. Moist, alkaline riparian soils had a higher net CO 2 efflux than drier, more acidic upland soils; soil temperature had no detectable effect on CO 2 efflux. The composition of microbial communities was also significantly correlated to variations in soil moisture content and pH. Dominant bacterial phyla in riparian soils were Proteobacteria while those in upland soils were Acidobacteria, suggesting that these components of these respective soil communities are at least partially responsible for variations in CO 2 efflux. Together, these data suggest that patchiness in subalpine soil properties within a watershed drive variation in the composition of soil microbial communities and their C cycling activities.