Activation of Synergistic Plant-Soil-Biofertilizers Responses by Calcium and Phosphate: Mitigation of Salinity Stress

As salt-sensitive crops, the performance of legumes in resisting salinity should be improved through accessible, less expensive and commonly practiced alternatives. Our study investigated the potential benefits of coupling the activation of endogenous phosphate-solubilizing bacteria with calcium phosphate amendment, focusing on saline soil fertility, the activation of the plants' antioxidant defense mechanisms, and the phosphate solubilization efficiency of the PSBs in plants growing under salinity conditions. There were four factors in the experimental treatments; i) control (C), ii) two levels of salinity (NaCl) 0.3% and 0.9%, iii) two levels of calcium-phosphate (Ca-P): (21% Ca x 41%P), (48% Ca x 92% P) and iii) combined application (NaCl x Ca P), applied at the seedling stage. Salinity significantly reduced water uptake, physiological parameters and affected root growth strategy (-60%). PCA confirmed that stressed plants showed a positive association between antioxidant parameters which could related to overproduction of ROS, decreased phosphate solubilizing activity, destroyed soil and reduced plant tolerance to salt stress. Application of combined (NaCl x Ca-P) significantly improved the antioxidant response with accumulation of proteins and proline, increase in water uptake, chlorophyll pigments, maintain cell turgor, root hair density (70%), root hair length (71%), complete histological root formation, improved the physicochemical quality of the soil where EC decreased by about 20 % and pH became neutral, and increased the PSB number (80%). The use of Ca-P with salinity could reestablish physiological homeostasis, complete anatomy, and better plant growth. It also enhanced the physicochemical and biological properties of the saline soil. Interactivity in the plant-soil-rhizobacteria system could be a viable option to positively influence plant resilience against salt stress and saline soil rehabilitation.