Growth of atriplex halimus L. In sodium chloride salinated culture solutions as affected by the relative humidity of the air

A. halimus plants were grown in saline nutrient solution (Knop's), in growth chambers, under two different conditions of relative humidity of the air: 27 ± 3 % (dry) and 65±3% (humid). All other climatic factors (temperature, illumination, etc.) were identical. Relative humidity was programmed to remain constant irrespective of day and night temperature changes. The salinity range was 0 to -20 atm NaCl. Under dry air conditions typical optimum growth curves were obtained (final dry weight, relative growth rate, and height), with maximum growth always at about -5 atm. Under humid conditions no such optimum curves were obtained; growth was greatest in the non-saline controls and decreased with each increment in the salinity of the growth medium. Apparently small amounts of NaCI are needed by A. halimus in order to overcome the stress caused by low relative humidity of the air. Under conditions of low evaporative demand, salinity is harmful to growth at all concentrations.