Cross-Response of Sugar Beet to Different Salt Concentrations Under Drought Stress

Salinity and drought are two significant abiotic stresses that restrict crop production globally. While past research has primarily concentrated on crop responses to individual stresses, recent studies indicate that comprehending the combined effects of drought and salinity is essential for enhancing crop tolerance and productivity. This study aims to investigate the impact of single and combined stresses at varying concentrations of salt and drought on sugar beet. Chlorophyll content, net photosynthesis, stomatal conductance, intercellular CO₂, and transpiration in sugar beet increased by 13%, 15%, 4%, and 4%, respectively, while growth parameters also improved under low salinity conditions. Conversely, under drought and high salinity conditions, the carotenoid content and indicators of oxidative damage (malondialdehyde and electrolyte leakage) in sugar beet plants increased significantly by 50% and 67%, respectively, leading to a marked reduction in photosynthesis and severely inhibiting plant growth. However, under the combined effect of low salinity and drought, the relative water content, water potential, and chlorophyll content increased sequentially to 17%, 20%, and 29% percent, photosynthetic efficiency, nutrient content, and potassium (K⁺) content of the plants increased significantly. On the other hand, sodium (Na⁺) content decreased significantly compared to the single drought condition. Meanwhile, the activities of antioxidant enzymes, such as catalase, ascorbate peroxidase, peroxidase, and superoxide dismutase, were down-regulated by 10%, 19%, 3%, and 40% sequentially in plants under this combined condition. This suggests that under the combined conditions of low salinity and drought, sugar beet effectively mitigated the negative effects of drought on growth through mechanisms such as improved nutrient uptake, maintenance of water and ion balance, and regulation of antioxidant enzyme activities and that this synergistic effect was mainly attributed to the positive impact of ion balance and osmoregulation. In contrast, the combination of high salinity and drought exacerbated the adverse effects caused by individual stressors.