Effects of Spirulina platensis Extract on Growth, Photosynthesis, Metal Uptake, and Antimicrobial Activity in Moringa oleifera Under Salt Stress

Soil salinity is a major abiotic stress limiting crop productivity, particularly in arid and semi-arid regions. This study investigates the biostimulant and antimicrobial potential of Spirulina platensis (S. platensis) extract in enhancing the growth and physiological performance of Moringa oleifera under salinity stress (2000 ppm NaCl). Seeds were primed with aqueous Spirulina platensis extracts at 1%, 3%, and 5% for two hours prior to sowing. Results showed that 3% extract significantly improved seed germination (100%), chlorophyll a and b, carotenoids, and root length, while 5% extract enhanced shoot elongation and dry biomass. Nutrient analysis revealed elevated calcium, magnesium, and protein contents at 3% concentration, alongside enhanced carbohydrate accumulation. Antioxidant and stress-mitigating effects were attributed to bioactive compounds identified by GC-MS, including oleic and palmitic acids, 2,4-di-tert-butylphenol, linoleic acid esters, glycoside-like molecules, and prostaglandin A2-biotin. Moreover, the extract exhibited selective antimicrobial activity, particularly against Staphylococcus aureus and Proteus vulgaris. These findings suggest that Spirulina platensis extract serves as a multifunctional natural biostimulant capable of enhancing salt tolerance, nutrient assimilation in Moringa oleifera, and microbial resistance supporting its practical application in saline agriculture.