Elevated atmospheric CO2 concentration mitigates salt damages to safflower: Evidence from physiological and biochemical examinations.

The physiological and biochemical responses of salt-stressed safflower to elevated CO 2 remain inadequately known. This study investigated the interactive effects of high CO 2 concentration (700 ± 50 vs. 400 ± 50 μmol mol−1) and salinity stress levels (0.4, 6, and 12 dS m−1, NaCl) on growth and physiological properties of four safflower (Carthamus tinctorius L.) genotypes, under open chamber conditions. Results showed that the effects of CO 2 on biomass of shoot and grains depend on salt stress and plant genotype. Elevated CO 2 conditions increased shoot dry weight under moderate salinity stress and decreased it under severe stress. The increased CO 2 concentration also increased the safflower genotypes' relative water content and their K+/Na + concentrations. Also enriched CO 2 increased total carotenoid levels in safflower genotypes and improved membrane stability index by reducing H 2 O 2 levels. In addition, increased CO 2 level led to an increase in seed oil content, under both saline and non-saline conditions. This effect was particularly pronounced under severe saline conditions. Under conditions of high CO 2 and salinity, the Koseh genotype exhibited higher grain weight and seed oil content than other genotypes. This advantage is due to the higher relative water content, maximum quantum efficiency of photosystem II (Fv/Fm) , and K+/Na+, as well as the lower Na+ and H 2 O 2 concentrations. Results indicate that the high CO 2 level mitigated the destructive effect of salinity on safflower growth by reducing Na + uptake and increasing the Fv/Fm , total soluble carbohydrates, and membrane stability index. This finding can be used in safflower breeding programs to develop cultivars that can thrive in arid regions with changing climatic conditions. • Elevated CO 2 reduced Na + uptake, mitigating the adverse effects of salinity. • Elevated CO 2 levels increased seed oil concentration, especially in severe saline conditions. • Koseh and C411 genotypes exhibited the highest positive response in grain weight to increasing CO 2 concentrations. • The superior grain weight and oil content of the Koseh genotype under high CO 2 and salinity were attributed to maintained K+/Na+, RWC and Fv/Fm levels. • Safflower's ability to withstand the interplay between atmospheric CO 2 , salt stress, and physiological functions as a resilient alternative crop. [ABSTRACT FROM AUTHOR]