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 (O-2) limitation of decomposition. Increased O-2 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 O-2 and C gas emissions is therefore critical to predict the partitioning and rate of C release from histosols under greater O-2 availability. We varied gas-phase O-2 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 O-2 concentrations, and rates were best described by log-linear model fits. The non-linear response of CO2 and CH4 emissions to O-2 concentration indicates that moist, C rich histosols may be highly sensitive to increases in O-2 availability, even below concentration thresholds typically classified as anoxic.