The Role of Arbuscular Mycorrhizal Fungi in Alleviation of Salt Stress

Soil salinity is a major abiotic stress adversely affecting plant growth and crop production worldwide. Increased salinization of arable land is expected to have destructive universal effects, resulting in 30 % land loss within the next 25 years and up to 50 % by the middle of twenty-first century (Porcel et al. 2012; Kapoor et al. 2013; Abdel Latef and Chaoxing 2014). The term ‘‘salinity’’ refers to the accumulation of excessive salts, in the sodic (or alkaline) and saline soils. Sodic soils having a poor soil structure generally are found over arid and semiarid regions, with high concentrations of Na at the exchangeable site of clay particles in the soil. Accordingly, the soil would have a great pH (greater than 8.5) with a high exchangeable sodium percentage (ESP [15). Saline soils can be generally found in arid regions, estuaries, and coastal fringes. Such kind of soils are dominated by Na ions with electrical conductivity (EC) more than 4 dS/m corresponding to the approximate concentration of 40 mM NaCl. Moreover, saline soils exhibit ESP of\15 and much lower pH values than the sodic soils (Horie et al. 2012). According to the potentail of plants to grow on high salt medium, plants are glycophytes or halophytes. Most plants are glycophytes and are not tolerant to salt stress. The early signs of salinity in plants are: