Association between CH4 uptake and N2O emission in grassland depends on nitrogen inputs

Abstract

Increasing nitrogen (N) input has been recognized as one of the important factors influencing methane (CH4) uptake and nitrous oxide (N2O) emission in arid and semiarid grasslands. Numerous studies have examined the spatiotemporal variations of CH4 and N2O fluxes in various ecosystems; however, the variation of the interplay between CH4 uptake and N2O emission with increasing N has not yet been well understood. This study explored the relationship between CH4 uptake and N2O emission in a semiarid grassland in Inner Mongolia, northern China, under a gradient of 12-year N additions. We found a synergistic relationship at low-N levels, where CH4 uptake and N2O emission are positively correlated. Conversely, an antagonistic interaction emerged with a negative correlation between CH4 uptake and N2O emission observed at high-N levels, which was evidenced by a 33.62% decrease in CH4 uptake and a 264.91% increase in N2O emission. Further independent analysis, covering at least five N addition levels across grassland ecosystems in China, confirmed the general pattern: three of four cases showed a synergistic relationship at low-N levels and an antagonistic relationship at high-N levels. Given the increasing N deposition in the future, the dynamics between CH4 uptake and N2O emission are critical for understanding the impact of external N input on net greenhouse gas emission and consequent global climate change.