Growth and ion distribution in salt stressed Melilotus indica (L.) All. and Medicago sativa L.

Abstract

Responses of two populations of Melilotus indica (L.) All., one from a non-saline soil and the other from a salt-affected field, to NaCl were assessed in a pot experiment and compared to alfalfa (Medicago sativa L.) whose salt tolerance had already been determined in a number of previous studies. Both populations of M. indica produced significantly greater shoot fresh and dry biomass than M. sativa after six weeks growth under varying NaCl concentrations. The M. indica population from salt-affected area was slightly superior to that of the normal population. The salt tolerant population of M. indica contained higher amounts of shoot Na+, K+ and Ca2+ contents per plant than M. sativa. Relatively high K/Na and Ca/Na ratios and K versus Na selectivity accounted for its vigorous growth. By contrast, the relatively low biomass producing M. sativa retained large proportions of Na+ and Cl− in its roots with little transport of these ions to shoots. Roots also accumulated high amounts of both K+ and Ca2+ which maintained root K/Na and Ca/Na ratios high under saline conditions. The non-saline population of M. indica had similar Na+ in the shoots as M. sativa, bud had the highest K/Na ratios. Thus the saline population of M. indica possesses higher salt tolerance than M. sativa. Ecotypic variation in salt tolerance exists in M. indica. In this study salt tolerance of M. indica is associated with ion inclusion and this species maintained shoot K/Na and Ca/Na ratios and K versus Na selectivity high.