Methane emissions from thermokarst lakes amplified by nutrient release upon permafrost thaw

Thermokarst lakes have been widely observed to function as strong atmospheric methane (CH₄) sources. The warming-induced development of thermokarst lakes is simultaneously accompanied by a considerable release of nutrients, which may in turn exhibit reverberation on CH₄ emissions. However, the effect of a coupled carbon and nutrient cycle on CH₄ emissions has yet been explored in any experimental studies. Here, by conducting in-situ nutrient addition experiments at two representative sites, coupled with incubating sediments from thermokarst lakes at 30 sites across a 1,100-km permafrost transect on the Tibetan Plateau, we explore the response of CH₄ emissions to nutrient input across thermokarst lakes. We find that nitrogen input accelerates CH₄ emissions by 38.6-54.4%, while phosphorus input doesn’t generate additional effects. Random forest model analysis reveals that methanogen is the dominant driver for the intensity of positive nitrogen effect, which is confirmed by the increased RNA-methanogenic abundance after nitrogen input. These results demonstrate that nutrient release upon permafrost thaw will enhance CH₄ emissions from thermokarst lakes, highlighting that their enhancements should be considered by land surface models when projecting CH₄ fluxes in permafrost regions under warming climate.