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 degrees C and 5 degrees 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 degrees 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.