Atmospheric CO₂ concentration is elevated globally, which has “CO₂ fertilization effects” and potentially improves plant photosynthesis, yield, and productivity. Despite the beneficial effect of CO₂ fertilization being modulated by vapor pressure deficit (VPD), the underlying mechanism is highly uncertain. In the present study, the potential roles of hormones in determining CO₂ fertilization effects under contrasting high and low VPD conditions were investigated by integrated physiological and transcriptomic analyses. Beneficial CO₂ fertilization effects were offset under high VPD conditions and were constrained by plant water stress and photosynthetic CO₂ utilization. High VPD induced a large passive water driving force, which disrupted the water balance and consequently caused plant water deficit. Leaf water potential, turgor pressure, and hydraulic conductance declined under high VPD stress. The physiological evidence combined with transcriptomic analyses demonstrated that abscisic acid (ABA) and jasmonic acid (JA) potentially acted as drought-signaling molecules in response to high VPD stress. Increased foliar ABA and JA content triggered stomatal closure to prevent excessive water loss under high VPD stress, which simultaneously increased the diffusion resistance for CO₂ uptake from atmosphere to leaf intercellular space. High VPD also significantly increased mesophyll resistance for CO₂ transport from stomatal cavity to fixation site inside chloroplast. The chloroplast “sink” CO₂ availability was constrained by stomatal and mesophyll resistance under high VPD stress, despite the atmospheric “source” CO₂ concentration being elevated. Thus, ABA- and JA-mediated drought-resistant mechanisms potentially modified the beneficial effect of CO₂ fertilization on photosynthesis, plant growth, and yield productivity. This study provides valuable information for improving the utilization efficiency of CO₂ fertilization and a better understanding of the physiological processes.

全球大气CO ₂浓度升高，具有“CO ₂施肥效应”，有可能提高植物光合作用、产量和生产力。_{尽管CO 2}施肥的有益效果是通过蒸气压不足（VPD）调节的，但其潜在机制高度不确定。在本研究中，通过综合生理学和转录组分析，研究了在对比高和低VPD条件下激素在确定CO _{2受精效果中的潜在作用。}有益的CO ₂施肥效应在高VPD条件下被抵消，并受到植物水分胁迫和光合作用CO ₂利用的限制。高VPD会产生较大的被动水驱动力，破坏水平衡，导致植物水分亏缺。在高 VPD 胁迫下，叶水势、膨压和导水率下降。生理证据与转录组分析相结合表明，脱落酸 (ABA) 和茉莉酸 (JA) 可能充当响应高 VPD 胁迫的干旱信号分子。叶面ABA和JA含量的增加触发了气孔关闭，以防止在高VPD胁迫下过度失水，同时增加了从大气到叶细胞间隙吸收CO ₂的扩散阻力。高VPD还显着增加了叶肉对CO ₂从气孔运输到叶绿体内固定位点的抵抗力。尽管大气“源”CO ₂浓度升高，但叶绿体“库”CO ₂可用性在高VPD胁迫下受到气孔和叶肉阻力的限制。因此，ABA和JA介导的抗旱机制可能改变CO ₂施肥对光合作用、植物生长和产量的有益影响。_{该研究为提高CO 2}施肥的利用效率和更好地理解其生理过程提供了有价值的信息。