Non-linear response of carbon dioxide and methane emissions to oxygen availability in a drained histosol

Organic-rich wetland soils in the histosol soil order represent the largest soil carbon (C) pool globally. Carbon accumulation in these ecosystems is largely due to oxygen (O2) limitation of decomposition. Increased O2 availability from wetland drainage and climate change may stimulate C decomposition overall and affect the balance of carbon dioxide (CO2) and methane (CH4) greenhouse gas release. Characterizing relationships, including non-linearity, between soil O2 and C gas emissions is therefore critical to predict the partitioning and rate of C release from histosols under greater O2 availability. We varied gas-phase O2 concentration from 0.03 to 20 % in incubations of a sapric histosol and measured resulting CO2 and CH4 emissions. Efflux of CO2 increased and CH4 emissions decreased at higher O2 concentrations, and rates were best described by log-linear model fits. The non-linear response of CO2 and CH4 emissions to O2 concentration indicates that moist, C rich histosols may be highly sensitive to increases in O2 availability, even below concentration thresholds typically classified as anoxic.