Co-inoculation of saline-tolerant Rhizobacteria and silica application modulates physiological responses of soybean under salinity stress

Abstract

Salinity is a major abiotic stress limiting legume productivity in coastal agroecosystems. This study investigated the efficacy of co-inoculating indigenous saline-tolerant Rhizobium sp. and Phosphate-Solubilising Bacteria (PSB) (Enterobacter cloacae), combined with silica (Si) fertiliser, on the growth and physiology of Anjasmoro soybean variety in saline soil (EC 4.12 dS m-1). The experiment employed a Factorial Randomised Block Design (3 x 3) with 3 replications. The first factor was microbial inoculation (Control, 6 g and 12 g seed-1) and the second was silica dosage (0, 150 and 300 kg ha-1). Results indicated that while vegetative morphology showed no significant variance due to high salinity suppression, physiological markers were significantly affected. Co-inoculation at 12 g seed-1 significantly increased chlorophyll content compared to the control (P < 0.05). Furthermore, inoculated plants exhibited lower proline levels compared to non-inoculated controls, suggesting successful stress mitigation by the rhizobacteria, thereby reducing physiological requirement of the plant for osmoprotectant accumulation. These findings suggest that while structural growth recovery in highly saline soils may require longer remediation, bio-inoculants effectively improve the physiological competence of soybeans.