Divergent Responses of CH4 Emissions and Uptake to Global Change Drivers

Abstract

Global changes strongly affect methane (CH₄) emissions and uptake. However, it is unclear how CH₄ emissions and uptake across rice paddy fields, uplands, and natural wetlands are affected by global change drivers, including nitrogen (N) addition, elevated carbon dioxide (eCO₂), warming (W), and precipitation (P). Here, we collected 1,250 observations of manipulated experiments from 303 publications during 1980–2020, encompassing 1,154 observations of single-factor experiments and 96 observations of two-paired experiments, and analyzed the effects of global change drivers on CH₄ emissions and uptake. Results showed CH₄ emissions were stimulated by eCO₂, W, and increased P (IP). CH₄ uptake was inhibited by N and IP but significantly enhanced by W and decreased P. The combined effects of the four global change drivers significantly inhibited CH₄ uptake (−9[−12, −6] %) and stimulated CH₄ emissions (13[7, 19] %). Two-factor interactions significantly reduced CH₄ emissions (−15[−27, −1] %) and insignificantly reduced uptake (−10[−19, 0] %). The interactive effects of any two global change drivers were mostly antagonistic. Random forest analysis indicated that the important factors affecting the responses of CH₄ emissions or uptake to different global change drivers varied. The structural equation model confirmed that climate, soil properties, and wetness index consistently played a remarkable role in regulating the responses of CH₄ emissions and uptake to global change drivers. This synthesis highlights an urgent need to consider the individual and interactive effects of multiple global change drivers on CH₄ emissions and uptake for a better understanding of the methane-climate feedback.