Potential effect of non-nitrogen fixing cyanobacteria Spirulina platensis on growth promotion of wheat (Triticum aestivum L.) under salt stress

Numerous microalgae have been used as modern eco-friendly biostimulants under abiotic stress conditions; however, the application of non-nitrogen fixing cyanobacteria, such as Spirulina (Arthrospira platensis) has not been extensively investigated. In this study, the effects of A. platensis (60 mg/L) applied twice as a foliar application on the growth, photosynthetic pigments, and oxidative metabolism of Triticum aestivum seedlings grown under salt stress (150 mM) were evaluated. Under salt stress conditions, growth attributes such as shoot and roots fresh weights, lengths, and photosynthetic pigments were significantly inhibited compared to the control group. Treatment with A. platensis effectively improved all growth parameters. Under salt stress conditions, shoot fresh weight and length increased by 49% and 44%, respectively, while root fresh weight and length were enhanced by 105% and 223%. The contents of chlorophyll a, b, and carotenoids in wheat were significantly reduced by 57%, 35%, and 43%, respectively. Additionally, seedlings exposed to salinity showed improved accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), along with decreased peroxidase (POD) enzyme activity. Spirulina extract (SPE) mitigated salt and induced oxidative stress by enhancing the activities of antioxidant enzymes. Furthermore, SPE protected wheat seedlings from the detrimental effects of H₂O₂ by promoting secondary metabolite biosynthesis. Additionally, SPE increased the proline content by 25%, aiding in the regulation of osmotic stress. Taken together, the results of this study support the application of A. platensis as an effective biostimulant for improving wheat growth and food security by reducing the harmful impacts of salt stress in semi-arid regions.