Data from: Elevated CO2 and temperature increase soil C losses from a soybean-maize ecosystem

Warming temperatures and increasing CO2 are likely to have large effects on the amount of carbon stored in soil, but predictions of these effects are poorly constrained. We elevated temperature (canopy: +2.8 °C; soil growing season: +1.8 °C; soil fallow: +2.3 °C) for three years within the 9th-11th years of an elevated CO2 (+200 ppm) experiment on a maize-soybean agroecosystem, measured respiration by roots and soil microbes, then used a process-based ecosystem model (DayCent) to simulate the decadal effects of warming and CO2 enrichment on soil C. Both heating and elevated CO2 increased respiration from soil microbes by ~20%, but heating reduced respiration from roots and rhizosphere by ~25%. The effects were additive, with no heat x CO2 interactions. Particulate organic matter and total soil C declined over time in all treatments and were lower in elevated CO2 plots than in ambient plots, but did not differ between heat treatments. We speculate that these declines indicate a priming effect, with increased C inputs under elevated CO2 fueling a loss of old soil carbon. Model simulations of heated plots agreed with our observations and predicted loss of ~15% of soil organic C after 100 years of heating, but simulations of elevated CO2 failed to predict the observed C losses and instead predicted a ~4% gain in soil organic C under any heating conditions. Despite model uncertainty, our empirical results suggest that combined, elevated CO2 and temperature will lead to long term declines in the amount of carbon stored in agricultural soils.气温升高与二氧化碳（CO₂）浓度上升均可能对土壤碳储量产生显著影响，但当前对这类影响的预测尚缺乏严格约束。本研究在一个玉米-大豆农田生态系统的二氧化碳浓度升高（+200 ppm）实验的第9至11年间，开展了为期三年的增温处理：冠层增温2.8℃，土壤生长季增温1.8℃，土壤休耕期增温2.3℃；期间测定了根系与土壤微生物的呼吸速率，并基于过程型生态系统模型（DayCent）模拟了增温与二氧化碳富集对土壤碳的十年尺度影响。增温与二氧化碳浓度升高均使土壤微生物呼吸速率提升约20%，但增温会使根系与根际呼吸速率降低约25%。二者的影响呈加和效应，未观测到增温与二氧化碳的交互作用。各处理组的颗粒态有机质与总土壤碳均随时间推移出现下降，且二氧化碳浓度升高样地的该指标显著低于对照样地，但不同增温处理组间无显著差异。我们推测，这类下降现象反映了激发效应：二氧化碳浓度升高下碳输入的增加，促进了老旧土壤碳的流失。增温样地的模型模拟结果与实测数据吻合，预测经过100年增温后，土壤有机碳将损失约15%；但针对二氧化碳浓度升高处理的模型模拟未能契合实测的碳流失现象，反而预测在任意增温条件下，土壤有机碳均会出现约4%的增幅。尽管模型存在不确定性，但本研究的实测结果表明，二氧化碳浓度升高与气温升高的共同作用将导致农田土壤碳储量出现长期下降。