Biomass production, nodulation, and acetylene reduction activity of alfalfa grown under salinity stress

The effect of salinity on biomass production, nodule formation and root acetylene reduction activity (ARA) in alfalfa (Medicago sativa L.) was investigated under field conditions. Seeds of alfalfa cv. Batini inoculated with one of four different Rhizobium strains were planted in washed loamy sand-filled transparent PVC cylinders arranged concentrically in plastic pots embedded in soil with the rims just above the soil surface. Salinization of plants commenced one week after emergence up to 16 weeks. Nitrogen (N)free nutrient solutions of different concentrations (full strength and 0.05 strength) were also applied during this period. Tap water (0.8 dS m^-1) served as control for the nutrient solution treatments as well as the salinity treatments which included 6.4 dS m^-1 and 12.2 dS m^-1 prepared with NaCl. The Rhizobium strains were TAL 380, TAL 1372, TAL 1373, and Buraimi. Increased salinity was associated with reduced shoot dry weights, root nodulation and ARA. Of the four Rhizobium strains, the order of efficiency in nodulation was Buraimi > TAL 1372 > TAL 1373 > TAL 380. This order was maintained in biomass the production. The detrimental effects of salinity appeared to be ameliorated by application of nutrient solutions, with the full strength being more effective than the 0.05 strength.