Warming temperatures and elevated CO₂ are inextricably linked global change phenomena, but they are rarely manipulated together in field experiments. As a result, ecosystem-level responses to these interacting facets of global change remain poorly understood. Here we report on a four-year field manipulation of warming and elevated CO₂ in a coastal wetland. Contrary to our expectations, elevated CO₂ combined with warming reduced the rate of carbon accumulation due to increases in plant-mediated oxygen flux that stimulated aerobic decomposition via oxygen priming. Evidence supporting this interpretation includes an increase in soil redox potential and a decrease in the nominal oxidation state of the dissolved organic carbon pool. While warming alone stimulated methane (CH₄) emissions, we found that elevated CO₂ combined with warming reduced net CH₄ flux due to plant–microbe feedbacks. Together, these results demonstrate that ecosystem responses to interacting facets of global change are mediated by plant traits that regulate the redox state of the soil environment. Thus, plant responses are critical for predicting future ecosystem survival and climate feedbacks.

气温升高和 CO ₂升高与全球变化现象有着千丝万缕的联系，但它们很少在实地实验中同时进行处理。因此，人们对生态系统层面对全球变化这些相互作用方面的反应知之甚少。在这里，我们报告了对沿海湿地变暖和 CO ₂升高的四年实地操作。与我们的预期相反，升高的 CO ₂由于植物介导的氧通量增加，通过氧气启动刺激有氧分解，因此与变暖相结合降低了碳积累的速度。支持这种解释的证据包括土壤氧化还原电位的增加和溶解有机碳库标称氧化态的降低。虽然单独变暖刺激了甲烷 (CH ₄ ) 排放，但我们发现 CO ₂升高与变暖相结合减少了净 CH ₄植物-微生物反馈引起的通量。总之，这些结果表明，生态系统对全球变化相互作用方面的反应是由调节土壤环境氧化还原状态的植物性状介导的。因此，植物反应对于预测未来生态系统的生存和气候反馈至关重要。