Role of exopolysaccharide secreted by Chlorella vulgaris SSAU 8 and Desertifilum salkalinema SSAU 7 in fertility enhancement of saline soil.

Soil salinization has emerged as a major constraint to global agricultural productivity, severely disrupting soil structure, nutrient cycling, and plant establishment. This study evaluates the functional potential of the cyanobacterium Desertifilum salkalinema SSAU-7 and the microalga Chlorella vulgaris SSAU-8 as bio-ameliorants for saline soils. Both isolates demonstrated high salinity tolerance and exhibited key plant growth-promoting traits, including indole-3-acetic acid (IAA) and hydrogen cyanide (HCN) production. Under escalating salt concentrations, D. salkalinema SSAU-7 and the mixed consortium maintained stable photosynthetic activity and enhanced extracellular polymeric substance (EPS) secretion, while C. vulgaris SSAU-8 showed reduced photo-physiological performance at 10 g L⁻¹ salinity. Soil microcosm experiments revealed that microbial inoculation facilitated the development of biological soil crusts (BSCs), which significantly improved soil physicochemical properties over 75 days. Notably, treated soils exhibited reduced pH (7.5-8.0), a 209% increase in total organic carbon, a 10% enhancement in porosity, and an 8% reduction in bulk density. EPS emerged as a critical driver of soil aggregation and fertility restoration by integrating essential structural components within the saline matrix. The BSC-amended soils further promoted Oryza sativa germination and early seedling vigor, underscoring the agricultural relevance of these microbial consortia. Collectively, our findings establish cyanobacteria-microalgae co-cultures as a promising eco-engineering strategy for reclaiming saline landscapes and strengthening soil resilience under salt stress.