Microalgae- and cyanobacteria-derived phytostimulants for mitigation of salt stress and improved agriculture

Soil salinization poses severe abiotic stress that adversely affects plant growth and development, ultimately threatening global food security by inducing physiological abnormalities. In response to escalating nutrient demands, with global requirements quantified at 76 % for nitrogen and 87 % for phosphorus, modern agriculture is increasingly adopting sustainable practices to enhance nutrient recycling and reduce reliance on external inputs. Emerging sources of plant phytostimulants, such as microalgal and cyanobacterial biomass, show promise in augmenting crop yields and bolstering plant resistance to various abiotic factors, including salt stress. The efficacy of these microorganisms stems from their simplistic cellular structure, superior photosynthetic efficiency, capacity for heterotrophic growth, adaptability to varying environmental conditions, potential for metabolic engineering, and the abundance of valuable biomolecules (such as soluble amino acids, micronutrients, polysaccharides, and phytohormones) within their biomass. This review provides an analysis of the current research landscape concerning microalgae- and cyanobacteria-derived phytostimulants, highlighting their promise as an innovative and sustainable alternative to synthetic fertilizers in the agricultural sector. Moreover, it identifies various adaptive responses of plants to salinity stress and assesses the potential and challenges associated with the use of microalgae and cyanobacteria-based metabolites for developing new sustainable strategies to enhance crop tolerance to salinity stress.