Warming reduces soil CO2 emissions but enhances soil N2O emissions: A long-term soil transplantation experiment

Climate warming can accelerate soil organic matter decomposition and stimulate soil CO₂ and N₂O emissions. However, long-term climate warming and land-use changes in relatively high-latitude regions on soil CO₂ and N₂O emissions remain largely unexplored, posing challenges to climate change research. Therefore, we conducted a long-term soil transplant experiment (8 years) across three relatively high-latitude northeastern regions in China to study the impacts of climate warming and land-use changes (from cropland to grassland) on soil CO₂ and N₂O emissions. As the temperature increased by 3 °C and 5 °C, the soil CO₂ emissions from cropland were reduced by 59.07% and 56.87%, respectively, and those from grassland were reduced by 17.11% and 10.62%, respectively. The experiment duration, soil C storage, soil microbial abundance and soil moisture may be the main factors that explain why warming did not stimulate soil CO₂ emissions. Soil N₂O emissions increased by 76.57% in cropland and 263.81% in grassland as the temperature increased by 5 °C. Higher soil CO₂ and N₂O emissions were observed in grassland compared to cropland. Warming promoted aboveground plant biomass and indirectly promoted soil N₂O emissions, particularly in grassland. The effects of long-term warming on soil CO₂ and N₂O emissions exhibited contrasting patterns, with CO₂ emissions in relatively high-latitude and cold regions showing sensitivity to climate warming. When taking strategies to enhance soil C sequestration, consideration should be given to whether these strategies will be offset by stimulating soil N₂O emissions, which is crucial for mitigating global warming. Overall, the impacts of long-term natural field warming and land-use changes on soil CO₂ and N₂O emissions and associated controls provide new insights for mitigating climate change.