Microbial inoculants and their potential application in salinity management

Soil salinity is one of the main abiotic stresses limiting plant growth and health, thus affecting productivity and subsistence agriculture in tropical semiarid regions. Soil- and plant-associated microorganisms use efficient strategies for the healthy development of plants even under salt stress. Legumes have been recommended for the recovery of saline soils due to their ability to perform symbiosis with nitrogen-fixing bacteria. Plants inoculated with Rhizobia, in addition to absorbing more nutrients, show an improvement in the water status of their leaves and produce organic solutes that protect plant cells against desiccation. Arbuscular mycorrhizal fungi (AMF) establish physiological mechanisms that promote the absorption of nutrients by plants, making them efficient in water absorption, osmoregulation, and photosynthesis, thus reinforcing cell structure and antioxidant metabolism. In addition to mycorrhizae, a group of endophytic fungi known as dark septate endophytes (DSEs) is directly involved in plant resistance to salt stress. Plant growth-promoting bacteria (PGPB) also have mechanisms that induce salinity protection through induced systemic tolerance processes, such as biofilm formation, exopolysaccharide production, and osmotic adjustment. Furthermore, PGPB can produce ACC deaminase that blocks the biosynthesis of ethylene produced under saline conditions, hence triggering the development of arbuscular mycorrhiza. Coinoculation of AMF and PGPB can improve the growth and resistance of plants in saline soils, and it may be an efficient strategy to recover degraded environments.