Microbial mechanisms of interactive climate-driven changes in soil N₂O and CH₄ fluxes: A global meta-analysis

Soils represent both a source of and sink for greenhouse gases (GHG). Elevated temperature (eT) affects both the physical and biological factors that drive GHG emissions from soil and thus understanding the effects of rising global temperatures on terrestrial GHG emission is needed to predict future GHG emissions, and to identify mitigation strategies. However, uncertainty remains about the interactive effects of multiple climate factors across different ecosystems, complicating our ability to develop robust climate change projections. Therefore, a global meta-analysis of 1337 pairwise observations from 150 peer-reviewed publications (1990-2023) was conducted to assess the individual effect of eT and its combined effects with eCO₂ (eT + eCO₂), drought (eT + drought) and increased precipitation (eT + ePPT) on soil N₂O and CH₄ fluxes, microbial functional genes, and soil extracellular enzyme activities across grassland, cropland, and forestland ecosystems. Across the dataset, eT significantly increased N₂O emissions (21%) and CH₄ uptake (36%). Nitrogen cycling was consistently stimulated by eT, with NO₃^- and NH₄⁺ and the abundance of amoA-AOB gene increasing by 6%, 10%, and 18%, respectively. Soil water content (SWC) was reduced, whereas increases of 9% in soil organic carbon (SOC), 14% in microbial biomass carbon (MBC), and 10% in total plant biomass were found under eT. The stimulation of soil N₂O emissions by eT was maintained for all ecosystems when combined with other global change factors (ie., eT + eCO₂, eT + ePPT, and eT + drought). By contrast, effects of eT on CH₄ uptake and emissions were more variable when combined with other factors; for instance, eT + eCO₂ and eT + ePPT suppressed CH₄ uptake in grasslands. This study highlights the urgent need to study the microbial mechanisms responsible for combined global change effects on N₂O and especially CH₄ fluxes.