Divergent terrestrial responses of soil N2O emissions to different levels of elevated CO2 and temperature

Understanding the responses of soil nitrous oxide (N2O) emissions from terrestrial ecosystems to future CO2 enrichment and warming is critical for the development of mitigation and adaptation policies. The effects of continuous increase in elevated CO2 (EC) and elevated temperature (ET) on N2O emissions are not fully known. We synthesized 209 measurements from 70 published studies and carried out a meta‐analysis to examine individual and interactive effects of EC and ET on N2O emissions from grasslands, croplands and forests. On average, a significant increase of 23% in N2O emissions was observed under EC across all case studies. EC did not affect N2O emissions from grasslands or forests, but significantly increased N2O emissions in croplands by 38%. The extent of ET effects on N2O emissions was nonsignificant and there was no significant difference in N2O emission responses among these three terrestrial systems. ET only promoted N2O emissions in forest by about 32% when ET was less than 2°C. The interactive effect of EC and ET on N2O emissions was significantly synergistic, showing a greater increase than the sum of the effects caused by EC and ET alone. Our findings indicated that the combination of EC and ET substantially promoted soil N2O and highlighted the urgent need to explore its mechanisms to better understand N2O responses under future climate change.