The impact of elevated CO2 on methanogen abundance and methane emissions in terrestrial ecosystems: A meta-analysis

Methane (CH₄), one of the major greenhouse gases, plays a pivotal role in global climate change. Elevated CO₂ concentration (eCO₂) increases soil carbon storage, which may provide a valuable material base for soil methanogenic microorganisms and stimulating their growth, thereby ultimately affecting CH₄ emissions. Therefore, to comprehend the effect of eCO₂ on CH₄ emissions, we conducted a meta-analysis encompassing 398 datasets from 59 publications (total of 50 sample sites). The results show that eCO₂ promotes both the abundance of the functional methanogenic gene <i>mcrA</i> and CH₄ emissions. However, this enhancement is modulated by a range of factors, such as the eCO₂ duration, land use types and soil texture, and there are significant interactions. This study offers new insights into the effects of eCO₂ on CH₄ emissions across diverse ecosystems and the underlying driving forces, vital for predicting the response of global terrestrial ecosystems in the face of future climate change.