Wheat cultivars responses to drought stress and atmospheric CO2 concentration variability

The objective of this study was to assess the growth and biochemical responses of 23 wheat cultivars to different soil moisture levels (40% and 75% depletion of available soil water) and atmospheric CO₂ concentrations (400 ± 50 and 700 ± 50 μmol mol⁻¹). The findings showed that water scarcity stress lowered grain weight and shoot dry weight (ShDW) by decreasing leaf area (LA), Fv/Fm, chlorophyll, and carotenoid content, while increasing catalase activity (CAT), ascorbate peroxidase activity (APX), guaiacol peroxidase activity (GPX), 2,2-diphenyl-1-picrylhydrazyl scavenging capacity (DPPH), and leaf proline content (LPC). The effect of water deficit on the measured traits varied depending on the CO₂ concentration. On average, the effect of water deficit stress on decreasing grain weight and LA, and increasing root dry weight (RDW), APX, LPC, and DPPH under ambient CO₂ was greater than under elevated CO₂. Furthermore, the impact of elevated CO₂ on the studied traits was dependent on the soil moisture profile. Its effect on increasing ShDW and RDW was greater under control conditions, while its effect on decreasing APX, DPPH, Chla, Chlb, and Car content was greater under water deficit conditions. The effects of water stress and elevated CO₂ were also found to be cultivar-specific. Principal component analysis revealed relationship among genotypes and traits. In summary, selecting wheat cultivars should be done separately for different CO₂ and water conditions due to their varied responses. Cultivars #22 (Hidhab) and #16 (Sistan) perform well under ambient CO₂ and control soil moisture, while #22 (Hidhab) and #5 (Karaj) show potential for adapting to different CO₂ and soil moisture levels, resulting in significant grain weight. These cultivars hold promise for future research studies. Consequently, it is critical to consider atmospheric CO₂ levels when designing breeding and yield improvement programs for wheat cultivars under changing climate conditions, as it affects their drought tolerance traits.