Impact of water stress under ambient and elevated carbon dioxide across three temperature regimes on soybean canopy gas exchange and productivity

The present study investigated the interactive effects of three environmental stress factors elevated CO₂, temperature, and drought stress on soybean growth and yield. Experiments were conducted in the sunlit, controlled environment Soil-Plant-Atmosphere-Research chambers under two-level of irrigation (WW-well water and WS-water stress-35%WW) and CO₂ (aCO_2-ambient 400 µmol mol^-1 and eCO₂-elevated 800 µmol mol^-1) and each at the three day/night temperature regimes of 24/18 °C (MLT-moderately low), 28/22 °C (OT-optimum), and 32/26 °C (MHT-moderately high). Results showed the greatest negative impact of WS on plant traits such as canopy photosynthesis (P_Cnet), total dry weight (TDwt), and seed yield. The decreases in these traits under WS ranged between 40 and 70% averaged across temperature regimes with a greater detrimental impact in plants grown under aCO₂ than eCO₂. The MHT had an increased P_Cnet, TDwt, and seed yield primarily under eCO_2, with a greater increase under WW than WS conditions. The eCO₂ stimulated P_Cnet, TDwt, and seed yield more under WS than WW. For instance, on average across T regimes, eCO₂ stimulated around 25% and 90% dry mass under WW and WS, respectively, relative to aCO₂. Overall, eCO₂ appears to benefit soybean productivity, at least partially, under WS and the moderately warmer temperature of this study.