Effects of humic acid application on physiological and biochemical characteristics of safflower cultivars under salinity and cadmium contamination

This study aimed to assess the impact of humic acid application on three safflower genotypes (AC-Sterling, Arack 2811, and C111) cultivated in cadmium contaminated soil with varying levels of salinity (0, 50, 100, and 150 mM NaCl). The experiment showed that the salinity decreased the K/Na ratio, photosynthesis rate, chlorophyll content, root volume as well as shoot and root dry weight, while it increased the cadmium concentration and the activities of catalase, peroxidase and ascorbate peroxidase. Of particular interest, the C111 genotype demonstrated the lowest decline in K/Na ratio and photosynthesis and exhibited the least increase in cadmium absorption. Furthermore, the salinity-induced increase in the antioxidant activity was most pronounced in catalase. The humic acid application led to increased activities of antioxidant enzymes, K/Na ratio, photosynthesis rate, chlorophyll content, root volume, shoot dry weight, and root dry weight. The humic acid application, however, resulted in decreased cadmium concentration in Arak 2811 while it increased cadmium concentration in AC-Sterling and C111. This indicates that the positive effects of humic acid on biomass were more pronounced in the C111 genotype under lower salinity levels and mostly manifested in root growth rather than shoot growth. The superiority of C111 in terms of the response to humic acid was more attributed to catalase and peroxidase activation compared to ascorbate peroxidase. Overall, the results showed a significant variation among safflower genotypes regarding the plant physiological attributes and the cadmium content in response to the salinity and the humic acid application.