Dual inoculation by rhizobium and mycorrhiza mediates biochemical and physiological responses in salt-stressed alfalfa

Physiological and biochemical responses to a combination of rhizobium and mycorrhizal inoculations in relation to withstanding salt stress, particularly in forage species such as alfalfa ( Medicago sativa L.), are not fully understood. Hence, alfalfa plants were exposed to three levels of salinity (0, 60, and 120 mM NaCl) and six variants of inoculation: non-inoculation, Ensifer meliloti (Rhizobium), Funneliformis mosseae (Mosseae), Rhizophagus irregularis (Irregularis), Rhizobium + Mosseae, and Rhizobium + Irregularis. Salt increased proline, H 2 O 2 , malondialdehyde, and Na + concentrations, and antioxidative enzymes activities but it decreased K + concentration, K + /Na + , leaf area and plant growth, leading to 51% decrease in the dry mass of alfalfa. The smallest malondialdehyde and H 2 O 2 concentrations and greatest activities of antioxidative enzymes of alfalfa were found in the salt-stressed plants inoculated by Rhizobium + Irregularis and Irregularis. The greatest K + and protein concentrations of salt-stressed plants belonged to alfalfa inoculated with Rhizobium + Irregularis and Rhizobium. The greatest relative water content, P concentration, and growth attributes were detected in alfalfa plants inoculated by Irregularis and Rhizobium + Irregularis. The foregone examinations of a wide range of physiological, biochemical, and growth attributes propose the suitability of inoculation by Irregularis and Rhizobium + Irregularis for enhancing P nutrition and physiological capabilities of alfalfa to withstand the currently aggravating salinity, though their practical implications particularly for farmers in arid regions warrant field examinations.