PNNL

Abstract

Coastal terrestrial-aquatic interfaces (TAIs) are dynamic zones of carbon biogeochemical cycling influenced by landscape-scale salinity gradients. However, there is significant cross-system heterogeneity in salinity influences over TAI soil biogeochemical function, such as gas fluxes and dissolved organic carbon concentrations. One potential explanation for the lack of consistency is unrecognized variation in soil organic carbon chemistry and microbial communities. To provide a foundation for understanding the role of C chemistry and microbial communities on biogeochemical cycling in coastal soils, we evaluated associations among a landscape scale soil salinity gradient, molecular-level soil carbon chemistry, and microbial community assembly processes. Based on observations in related systems we hypothesized systematic shifts along the salinity gradient in organic carbon thermodynamics, biochemical transformation profiles, and heteroatom content. While the thermodynamic favorability of water soluble organic compounds in shallow soils did decrease with increasing salinity (R2=0.78, p