Suppression of Nitrogen Deposition on Global Forest Soil CH <sub>4</sub> Uptake Depends on Nitrogen Status
Xiaoyu Cen, Nianpeng He, Mingxu Li, Li Xu, Xueying Yu, Weixiang Cai, Xin Li, Klaus Butterbach‐Bahl
Abstract
Abstract Methane (CH 4 ) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH 4 . Uptake of CH 4 by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH 4 budget. However, it remains an unsolved puzzle why N input stimulates soil CH 4 uptake in some forests while suppressing it in others. Combining previous findings and data from N addition experiments conducted in global forests, we proposed and tested a “stimulating‐suppressing‐weakened effect” (“three stages”) hypothesis on the changing responses of soil CH 4 flux ( R CH4 ) to N input. Specifically, we calculated the response factors ( f ) of R CH4 to N input for N‐limited and N‐saturated forests across biomes; the phased changes in f values supported our hypothesis. We also estimated the global forest soil CH 4 uptake budget to be approximately 11.2 Tg yr −1 . CH 4 uptake hotspots were predominantly located in temperate forests. Furthermore, we quantified that the current level of N deposition reduced global forest soil CH 4 uptake by ∼3%. This suppression effect was more pronounced in temperate forests than in tropical or boreal forests, likely due to differences in N status. The proposed “three stages” hypothesis in this study generalizes the diverse effects of N input on R CH4 , which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH 4 uptake can be significantly increased in the N‐saturated forests in tropical and temperate biomes.