How do moisture changes influence root-derived methane cycling in wetland soils?

Anoxic wetland soils are the biggest natural source of methane (CH4) globally. Climate-driven changes to soil moisture regimes are expected to alter wetland CH4 production, consumption, and transport in a variety of different ways. At the same time, moisture changes also influence plants and their traits, especially belowground. Wetland plants provide key carbon substrates for methanogenesis, and transport CH4 to the atmosphere but also oxygen into the soils, which can promote CH4 consumption. We tested hypotheses on these complex abiotic and biotic interactions to understand how belowground plant traits influence net CH4 emissions in wetlands. Specifically, we address the following questions 1) which root traits are most important for wetland CH4 processes? 2) how does water table manipulation influence the link between root biomass and CH4? 3) how does soil moisture influence the amount of root-derived carbon emitted as CH4? First, using a literature review, we developed a conceptual framework describing root traits that would be most related to CH4 processes, highlighting trait categories regulating CH4 substrate provision and transport. Second, using a field manipulation in an experimental rice system, we found that root biomass and CH4 emissions are positively linked, but only under low moisture conditions. Lastly, in a lab incubation, we found that the amount of root-derived C-CH4 increases with increased fresh root litter, in water saturated peat soils. Overall, our studies identify root traits and their moisture interactions that should be considered in wetland CH4 measurements and models.