Data and code for: Suppression of nitrogen deposition on global forest soil CH4 uptake depends on nitrogen status

Methane (CH4) is the second most important atmospheric greenhouse gas (GHG) and forest soils are a significant sink for atmospheric CH4. Uptake of CH4 by global forest soils is affected by nitrogen (N) deposition; clarifying the effect of N deposition helps to reduce uncertainties of the global CH4 budget. However, it remains an unsolved puzzle why N input stimulates soil CH4 flux (RCH4) 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 RCH4 to N input. Specifically, we calculated the response factors (f) of RCH4 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 CH4 uptake budget to be approximately 11.2 Tg yr–1. CH4 uptake hotspots were located predominantly in temperate forests. Furthermore, we quantified that current level of N deposition reduced global forest soil CH4 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 RCH4, which could help improve experimental design. Additionally, our findings imply that by regulating N pollution and reducing N deposition, soil CH4 uptake can be significantly increased in the N-saturated forests in tropical and temperate biomes.

Specifically, Data Set S1 (CH4_exp dataset in main text) was used to derive the response factors of soil CH4 flux to N input in global forests; Data Set S2 (CH4_obs dataset in main text) was used to estimate the soil CH4 fluxes in global forests; Data Sets S3–S7 were used to classify the N-limited and N-saturated forests on global level; Data Set S8 contains environmental factors (MAT, MAP, soil texture, etc.) for global estimations on grid level; Data Set S9 contains global forest soil CH4 budgets reported in previous studies. The data analysis process and produced figures can be replicated with the uploaded R script (Code S1).