Rising atmospheric [CO₂] influences plant growth, development, productivity and stress responses. Soybean is a major oil crop. At present, it is unclear how elevated [CO₂] affects the physiological and biochemical pathways of soybean under drought stress. In this study, changes in the photosynthetic capacity, photosynthetic pigment and antioxidant level were evaluated in soybean at flowering stages under different [CO₂] (400 μmol mol⁻¹ and 600 μmol mol⁻¹) and water level (the relative water content of the soil was 75–85% soil capacity, and the relative water content of the soil was 35–45% soil capacity under drought stress). Changes in levels of osmolytes, hormones and signal transduction enzymes were also determined. The results showed that under drought stress, increasing [CO₂] significantly reduced leaf transpiration rate (E), net photosynthetic rate (P_N) and chlorophyll b content. Elevated [CO₂] significantly decreased the content of malondialdehyde (MDA) and proline (PRO), while significantly increased superoxide dismutase (SOD) and abscisic acid (ABA) under drought stress. Elevated [CO₂] significantly increased the transcript and protein levels of calcium-dependent protein kinase (CDPK), and Glutathione S- transferase (GST). The content of HSP-70 and the corresponding gene expression level were significantly reduced by elevated [CO₂], irrespective of water treatments. Taken together, these results suggest that elevated [CO₂] does not alleviate the negative impacts of drought stress on photosynthesis. ABA, CDPK and GST may play an important role in elevated CO₂-induced drought stress responses.

大气[CO ₂ ]的升高会影响植物的生长，发育，生产力和胁迫响应。大豆是主要的油料作物。目前，尚不清楚[CO ₂ ]的升高如何影响干旱胁迫下大豆的生理和生化途径。在这项研究中，在不同[CO ₂ ]（400μmolmol ^-1和600μmolmol ^-1）下，在开花期评估了大豆光合能力，光合色素和抗氧化剂水平的变化。）和水位（在干旱胁迫下，土壤的相对含水量为75-85％的土壤容量，土壤的相对含水量为35-45％的土壤容量）。还确定了渗透压，激素和信号转导酶水平的变化。结果表明，在干旱胁迫下，增加的[CO ₂ ]显着降低了叶片的蒸腾速率（E），净光合速率（P _N）和叶绿素b含量。升高的[CO ₂ ]显着降低了干旱胁迫下丙二醛（MDA）和脯氨酸（PRO）的含量，同时显着增加了超氧化物歧化酶（SOD）和脱落酸（ABA）的含量。升高[CO ₂]显着增加了钙依赖性蛋白激酶（CDPK）和谷胱甘肽S-转移酶（GST）的转录本和蛋白质水平。升高[CO ₂ ]可以显着降低HSP-70的含量和相应的基因表达水平，而与水处理无关。综上所述，这些结果表明升高的[CO ₂ ]不能减轻干旱胁迫对光合作用的负面影响。ABA，CDPK和GST可能在升高的CO ₂诱导的干旱胁迫响应中起重要作用。