Intensifying drought eliminates the expected benefits of elevated carbon dioxide for soybean

Stimulation of C3 crop yield by rising concentrations of atmospheric carbon dioxide ([CO2]) is widely expected to counteract crop losses that are due to greater drought this century. But these expectations come from sparse field trials that have been biased towards mesic growth conditions. This eight-year study used precipitation manipulation and year-to-year variation in weather conditions at a unique open-air field facility to show that the stimulation of soybean yield by elevated [CO2] diminished to zero as drought intensified. Contrary to the prevalent expectation in the literature, rising [CO2] did not counteract the effect of strong drought on photosynthesis and yield because elevated [CO2] interacted with drought to modify stomatal function and canopy energy balance. This new insight from field experimentation under hot and dry conditions, which will become increasingly prevalent in the coming decades, highlights the likelihood of negative impacts from interacting global change f...大气二氧化碳浓度（[CO2]）升高对C3作物（C3 crop）产量的刺激效应，长期以来被学界广泛认为可抵消本世纪干旱加剧所引发的作物减产。但此类预期均基于样本稀疏且偏向中生生长条件的田间试验。本项为期八年的研究依托一处独特的露天田间平台，通过降水调控与逐年气象条件波动开展实验，证实随着干旱程度加剧，高浓度二氧化碳（elevated [CO2]）对大豆产量的刺激效应会衰减至完全消失。与当前学界主流研究预期相悖的是，大气二氧化碳浓度升高并未缓解严重干旱对光合作用与产量的负面影响——其核心机制在于高浓度二氧化碳会与干旱产生交互作用，进而改变气孔功能与冠层能量平衡。这项在未来数十年将愈发普遍的高温干旱条件下开展的田间实验所获得的新认知，凸显了全球变化因子交互作用可能带来的负面影响……