PNNL

Abstract

As the global water cycle intensifies with ongoing climate change, we can expect increased frequency of both drought and flood. Water is an important driver of soil carbon dynamics, and it is crucial to understand how these moisture disturbances will affect carbon availability and fluxes in soils. We investigated the role of water in substrate-microbe connectivity and soil C cycling under extreme moisture conditions. We collected soils from Alaska, Florida, and Washington USA, and incubated them under Drought, Flood, and Field Moist conditions. An analysis of soil respiration, pore-water C, and microbial community composition demonstrated that drought had a stronger effect on these variables than flooding. Contrary to our expectations, soil response was not consistent across sites, and may be influenced by site-level factors like soil texture and moisture history. Sand-versus-clay content influences the potential for soil C stabilization, and differences in porosity can influence microbial access to substrates through the pore network. Further, the microbial communities are adapted to the historic stress conditions at their sites, and are therefore unlikely to respond to similar induced drought and flood stresses.