Salinity-Driven Shifts in PGPR Activity in Thane Mangrove Ecosystems

Mangrove ecosystems, such as those in Thane Creek, Maharashtra, exhibit pronounced zonation in plant species composition corresponding to salinity gradients—from oligohaline (low salinity) to polyhaline (high salinity) zones. These variations influence not only the above-ground flora but also the below-ground microbial communities, especially Plant Growth-Promoting Rhizobacteria (PGPR), which play a critical role in nutrient cycling, stress mitigation, and plant resilience. This study investigates the salinity-mediated functional diversity of PGPR in rhizospheric soils from five representative sites across the salinity gradient of Thane Creek. Bacterial strains were isolated and assessed for halotolerance and key plant-beneficial traits such as indole-3-acetic acid (IAA) production, nitrogen fixation, phosphate solubilization, potassium and zinc mobilization, and hydrolytic enzyme activities (amylase, cellulase, protease). Soil physicochemical parameters were also analyzed to correlate environmental conditions with microbial functionality. Results revealed significant shifts in PGPR activity across zones, with halotolerant strains from polyhaline zones exhibiting enhanced enzyme production and nutrient mobilization capabilities. These findings suggest that salinity is a major ecological driver shaping PGPR functional potential. Understanding such microbe-plant-environment interactions provides valuable insights for deploying PGPR in sustainable agriculture, particularly for crop improvement in saline and marginal lands. The study also underscores the potential of mangrove-associated microbes in biotechnological applications and reforestation programs in salt-affected areas.