Wetland CH4 and CO2 emissions show opposite temperature dependencies along global climate gradients

Abstract

Methane (CH₄) and carbon dioxide (CO₂) are the two largest contributors to the anthropogenically-driven greenhouse effect, which are the dominant gaseous end-products of wetland C decomposition. However, given our limited understanding of the spatial heterogeneity of wetland CH₄ and CO₂ emissions, it is uncertain how future warming may impact the emissions of these dangerous emissions. Here, we show opposite temperature dependencies of CH₄ and CO₂ emissions along global climate gradients using data from 45 widely distributed wetlands in the FLUXNET-CH₄ database. Specifically, the temperature dependence of CH₄ emissions increased as mean annual temperature (MAT) rose, while the dependence of CO₂ emissions decreased, suggesting that in warmer areas, there is a greater risk for increased wetland CH₄ emissions accompanying lower CO₂ emissions in response to global warming. The ratio of wetland CH₄ to CO₂ emissions increased linearly with increasing temperature only when MAT and mean annual precipitation (MAP) are greater than 4.7 °C and 483 mm, respectively. This response indicates that, compared with those in cold and dry climates, wetland ecosystems in warmer and wetter climates are more prone to methanogenesis as temperatures rise. Our results suggest that neglecting spatial variation of temperature dependencies in models may underestimate wetland CH₄ and CO₂ emissions compared to the use of a static and consistent temperature dependence parameter when only considering temperature effects. These findings highlight the importance of incorporating climate-related variation in the temperature dependencies of CH₄ and CO₂ emissions into models to improve predictions of wetland C-climate change feedbacks in the Anthropocene.