Impact of warming on microorganisms and soil organic matter cycling with depth in soils

Soils store approximately 1,300–1,600 Pg of organic carbon in the top meter. However, despite a lower carbon concentration, subsoil horizons (<0.3 m) contain more than half of global soil organic carbon. In deeper soils the cycling of soil carbon is proposed to be slower but its vulnerability to projected climate change is still under debate. As in surface soils, deep soil microorganisms are responsible for both the decomposition and the formation of soil organic matter (SOM) and their response in terms of biomass, activity, composition and function may be key to determine how environmental change will alter deep carbon turnover and nutrient cycling. Here we explore how warming across a whole soil profile impacts microbial community composition and decomposition of SOM. We have established a soil warming experiment at the Blodgett Forest Research Station, CA, with warming of +4°C to >1 m depth relative to the natural soil temperature gradient. Samples were taken along the soil profile and initial results comparing pre-warming to six months post warming initiation are being compared. Alterations in microbial community composition were analyzed via 16S rRNA gene sequencing and changes in the decomposition potential of SOM were assessed via extracellular enzyme activity measurements. In this ongoing experiment, we aim to understand the microbial contribution to the turnover of SOM at different soil depths and how microbial responses to projected increases in atmospheric temperature might impact SOM stability.