Hydrological controls on soil carbon dynamics: from pores to cores

Core-scale soil carbon fluxes are ultimately regulated by pore-scale dynamics of substrate availability and microbial access, which are strongly influenced by soil water. The global water cycle is intensifying, and moisture extremes like drought and flood are increasing in frequency and intensity. It is therefore important to understand how these changing moisture regimes will affect carbon availability and fluxes in soils. We conducted two laboratory incubation experiments to investigate how drought and flood altered soil carbon availability and mineralization. Antecedent moisture conditions were found to be an important control on soil carbon availability, as soil respiration and carbon availability showed distinct hysteresis during drying and rewetting. Additionally, when comparing impacts of drought and flood across different soils, the soil carbon response was not consistent across sites, and was influenced by site-level pedological and environmental factors such as soil texture and historic stress conditions. These studies highlight the importance of pore-scale physicochemical and biochemical properties when studying soil biogeochemical transformations at the core scale.