Effects of Rhizobium leguminosarum Inoculation on Growth, Nitrogen Uptake and Mineral Assimilation in Vicia faba Plants under Salinity Stress

Salt stress constitutes one of the most significant environmental constraints that limit legume production, especially in arid and semiarid regions. This study aimed to evaluate the effect of salt stress (0, 60, and 120 mM of NaCl) on growth, nodulation process, nitrogen uptake and mineral nutrition content of Vicia faba L. plants inoculated with native Moroccan rhizobia isolated from root nodules of faba bean plants grown in the MarrakechHaouz region. Three Rhizobium leguminosarum strains (RhOF34, RhOF125 and RhOF15), which had different tolerance to salinity, were used to inoculate faba bean plants. The results showed that chronic exposure to salinity affected growth and symbiotic parameters of V. faba differently. Shoot biomasses were reduced under salinity stress especially in the plants inoculated with the salt sensitive strain (RhOF15). The nodulation of faba bean roots sharply decreased under 120 mM salt treatment, particularly with the sensitive Rhizobium strain. The total nitrogen content decreased with increasing salinity, except for the plants inoculated with the tolerant strain RhOF34, which kept a high nitrogen content. Sodium and calcium concentration increased sharply in plant tissues with increasing salt stress, while the potassium concentration decreased. RhOF34 strain reduced Na^+, Ca^2+ and K^+ absorption by faba bean plants. Inoculation with the salt tolerant strains RhOF125 and RhOF34 led to an increased plant biomass, nodules number, and nitrogen content; and seemed to protect faba bean plants against the toxic effects of salinity.