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 3 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, and 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 × 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浓度上升可能对土壤碳储量产生显著影响，但目前针对这类影响的预测仍缺乏严格约束。本研究在玉米-大豆农田生态系统的增二氧化碳（浓度提升200 ppm）实验开展至第9至11年期间，实施了为期3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，并采用基于过程的生态系统模型（process-based ecosystem model，DayCent）模拟增温与二氧化碳富集对土壤碳的年代际影响。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，未观测到温度与二氧化碳的交互作用。所有处理组的颗粒态有机质与总土壤碳均随时间下降，且二氧化碳富集样地的碳储量低于环境空气对照样地，但不同增温处理组间无显著差异。我们推测，这类碳储量下降反映了激发效应（priming effect）：二氧化碳浓度升高下碳输入量增加，驱动了老土壤碳的损耗。增温样地的模型模拟结果与实测数据吻合，且预测经100年增温后，土壤有机碳将损失约15%；但针对二氧化碳富集处理的模拟未能复现观测到的碳损耗，反而预测无论是否伴随增温，土壤有机碳均会增加约4%。尽管模型存在不确定性，但本研究的实测结果表明，二氧化碳富集与增温共同作用下，农业土壤的碳储量将出现长期下降。