Halotolerant Microbes for Amelioration of Salt-Affected Soils for Sustainable Agriculture

Abstract

Soil salinity is one of the major abiotic stresses that adversely affect the sustainable agricultural production globally. About 20% of the total land area is affected by salinity, and the area is increasing at an alarming rate. There is a damaging effect of salinity on soil microbial communities, and their activities have been reported in majority of the studies. Excess accumulation of salts in the root zone often deteriorates the soil properties, viz. physical, chemical and biological to such an extent that crop production is adversely affected. Also, salt-affected soils are poor in organic matter content and thus the biomass as well as microbial activity, thereby affecting the microbiologically mediated processes required for plant growth. The methods available for reclamation of salt-affected soils are not cost effective, and further the availability of good-quality waters required for leaching salts in saline soils and mineral gypsum or organic amendments for sodic soils is scarce. Halotolerant and halophilic microorganisms having plant growth-promoting (PGP) traits have the potential to assuage salt stress and enhance plant growth and production in salt-affected soils. These plant growth-promoting rhizobacteria (PGPR) tolerate wide range of salt stress and thus enable plants to withstand salinity by different mechanisms such as hydraulic conductance, osmotic accumulation, sequestering toxic Na+ ions, maintaining the higher osmotic conductance and photosynthetic activities. The halophilic microbes have the potential to influence direct growth promotion of plants by fixing atmospheric nitrogen, solubilizing insoluble nutrients and secreting hormones such as IAA, GAs and kinetins besides ACC deaminase production, which helps in regulation of ethylene. Some of the recent researchers have confirmed the possibility of using halophiles in recovery of salt-affected soils and sustain agricultural production in degraded lands. We also observed beneficial effects of using PGP halophilic bacteria isolated from the native salty soils for enhancing crop production under salt stress conditions. For easy application in agriculture, liquid bioformulations have been prepared for efficient strains, and their use has enhanced the yield of rice and wheat by 11–14% and also for other crops like mustard, vegetables and fodder crops under salt stress conditions. Therefore, the bioremediation approach being cheap and eco-friendly is being promoted to optimize crop yields under sodic and saline-sodic soils of the Indo-Gangetic plains of north India.