Effect of mycorrhizal inoculation on growth, nitrogen fixation and nutrient uptake in alfalfa (Medicago sativa) under salt stress

Abstract

Most legumes in natural conditions form a symbiosis with arbuscular mycorrhizal (AM) fungi. AM fungi in saline soils have been reported to improve salinity tolerance and growth in plants. In the present study, interaction between mycorrhizal fungus, Glomus mosseae, and salinity stress in relation to plant growth, nitrogen fixation, and nutrient accumulation was evaluated in alfalfa (Medicago sativa). Two alfalfa cultivars (Bami and Yazdi) were compared under different levels of salinity with and without mycorrhizal inoculations. Salt stress resulted in a noticeable decline in shoot and root dry matter accumulation, resulting in a decline in the shoot to root ratio (SRR) in all plants. However, Bami was found to be more tolerant to salinity than Yazdi. Inoculated plants exhibited better growth and biomass accumulation under stressed as well as unstressed conditions. Mycorrhizal colonization (MC) was reduced with increasing salinity levels, but the mycorrhizal dependency (MD) increased, which was more evident in Yazdi. Nodulation was completely inhibited under salt stress conditions for both non - AM inoculated alfalfa varieties. Nodulation only occurred in inoculated plants. Nitrogenase activity was reduced with increasing salt concentrations. AM inoculated plants had considerably higher nodule numbers, dry weights, and nitrogenase activity under nonsaline environments. Bami had a comparatively lower Na+ concentration and higher K+ and Ca2+ concentrations than Yazdi. Although nitrogen (N) and phosphorus (P) contents declined with increasing salinity, Bami had higher levels of N and P, as compared with Yazdi. Plants inoculated with Glomus mosseae had better plant growth and nitrogen fixation under salt stress.