Role of beneficial microbial gene pool in mitigating salt/nutrient stress of plants in saline soils through underground phytostimulating signalling molecules

Abstract

Soil salinity diminishes soil health and reduces crop yield, which is becoming a major global concern. Salinity stress is one of the primary stresses, leading to several other secondary stresses that restrict plant growth and soil fertility. The major secondary stresses induced in plants under saline-alkaline conditions include osmotic stress, nutrient limitation, and ionic stress, all of which negatively impact overall plant growth. Under stressed conditions, certain beneficial soil microflora are known to have evolved phytostimulating mechanisms, such as the synthesis of osmoprotectants, siderophores, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity, phosphate solubilization, and hormone production, which enhance plant growth and development while mitigating nutrient stress. Beneficial soil-borne bacterial species such as Bacillus, Pseudomonas, and Klebsiella and fungal strains such as Trichoderma, Aspergillus, Penicillium, Alternaria, and Fusarium also aid in reducing salinity stress. Phosphate-solubilizing microorganisms also assist in nutrient acquisition via both enzymatic and non-enzymatic processes. In the case of enzymatic processes, they produce different enzymes such as alkaline phosphatases and phytases, whereas non-enzymatic processes produce organic acids such as gluconic, citric, malic, and oxalic acids. The native halotolerant/halophilic soil microbial gene pool with multifunctional traits and stress-induced gene expression can be developed as suitable bio-inoculants to enhance stress tolerance and optimize plant growth in saline soils.