A new framework for interpreting ex situ wetland methane production and consumption rates—data and code

Ex situ incubations are the primary method used to quantify rates of gross methane production and consumption, which together determine net wetland methane emissions. However, a clear framework for interpreting this data is lacking, and it remains unknown whether ex situ rates and their environmental drivers conform to trends expected from in situ ecological theory. We synthesized published rates of methanogenesis, aerobic methane oxidation, and anaerobic methane oxidation and used boosted regression tree models to identify key drivers. We found median aerobic methane oxidation rates were 2.7 times greater than those of methanogenesis—a paradox given wetlands are net methane sources. We demonstrate this discrepancy is an artifact of methodology: aerobic methane oxidation is measured as a potential rate, whereas methanogenesis is commonly measured as a substrate-limited rate. Within our methanogenesis dataset, potential rates were an order of magnitude higher than substrate-limited rates (p<0.001), confirming that these two assay types yield quantitatively distinct results. Our driver analysis suggests that 1. rates of methanogenesis are strongly controlled by labile carbon availability from the soil surface, 2. the balance between methanogenesis and anaerobic methane oxidation is shifting with warming, and 3. species-specific plant effects structure all pathways of methane production and consumption via rhizosphere interactions. This synthesis demonstrates the value of ex situ data for generating mechanistic hypotheses while highlighting the need for future research to prioritize minimally disruptive in situ measurements to obtain accurate rate magnitudes.