Salt Sensitivity of Chickpea During Vegetative Growth and at Different Humidities

Abstract

Two experiments were designed to determine whether salt stress of the salt-sensitive legume Cicer arietinum L. was associated with water stress or with ion excess. In the first experiment, shoot growth and the concentration of inorganic ions in cultivars L-550 and UC-5 were monitored for 26 days. In greenhouse solution cultures, 8-day-old plants received either no salt or 15 mM NaCl plus 7.5 mM Na2SO4 (- 0.115 MPa) and were then sampled 9 times over the 26-day growth period. Salt treatments and time period were factorially combined with two cultivars, in three replications. Control and salt-treated plants remained nearly identical in growth rate and shoot weight until about 10 days after the addition of salt. Then the relative growth rate of stressed plants declined to a steady low value. The decline corresponded with changes in shoot sodium and chloride concentrations, and not with the changes in shoot water potential and osmotic potential that occurred soon after the addition of Na salts. The shoot Na and CI concentrations gradually increased until the growth rate of the salt treated plants diverged from the controls near day 10. In the second experiment parameters of water status, ion accumulation, and ion distribution were correlated with growth of cultivars L-550 and E-100 at different humidities and salt levels. Plants grew for 6 weeks in four different growth chambers at relative humidities of 55, 75, 88 and 95%. The four salt levels were 0, 12, 24 and 36 mM Na added as sulfate and chloride in equal proportion on an equivalent basis. The lowest humidity (55%) resulted in the death of several salt-treated plants. At high humidity (95%) cv. E-100 was slightly more salt-sensitive than cv. L-550; but at low humidity (75%) cv. E-100 was the less sensitive cultivar and had the lower shoot Na concentration. Despite the confounding effects of three independent variables - salt level, cultivar, and humidity - shoot dry weight correlated closely with leaf and shoot Na concentration. None of the other measured parameters - shoot Cl, shoot water potential, or transpiration rate - correlated well with growth. Low humidity impaired growth only when it led to high shoot Na. Data from the two experiments suggest that salt primarily inhibits growth through accumulation of Na into the shoots.