Stomatal Conductance of Differentially Salinized Plants

Abstract

Stomatal resistance was measured daily with a stomatal diffusion porometer during a 4-week period in leaves of bean (Phaseolus vulgaris L., var. Bush Blue Lake) and barley (Hordeum vulgare L., var. Liberty) plants having roots equally split between two differentially salinized nutrient solutions. The stomatal conductance (reciprocal of stomatal resistance) of plants with half their roots in saline solutions was intermediate between the stomatal conductances of plants grown in non-saline solutions and those grown in saline solutions. Results from a previous experiment (4) showed that the degree of osmotic adjustment and the rate of growth of bean and barley plants were functions of the proportion of the root system exposed to saline conditions. Stomatal resistances were not measured in that study. The purpose of the experiment reported here was to determine the stomatal conductance of leaves when divided root systems were exposed to solutions of different osmotic potential. MATERIALS AND METHODS Experimental procedures were the same as reported before (4), except stomatal resistance was measured with a stomatal diffusion porometer (2). Water and osmotic potential energies of excised plant leaves were determined with thermocouple psychrometers at intervals during a 4-week period (February 1-March 4, 1971) in leaves of bean (Phaseolus vulgaris L., var. Bush Blue Lake) and barley (Hordeum vulgare L., var. Liberty) plants having roots equally divided between two differentially salinized nutrient solutions. Bean plants were grown in a growth chamber (25 C during day; 20 C during night; 12 hr light; 12 hr dark; 60 to 80% relative humidity; light quanta flux density during day of 45 nanoEinsteins cm-2sec'), and barley plants were grown in a growth room (30 C during day; 25 C during night; 15 hr light; 9 hr dark; 30 to 45% relative humidity; light quanta flux density during day of 24 nano-Einsteins cm-2sec-1). Both bean and barley plants were 21 days old at the beginning of the experiment. The bean plants were salinized in two-2-bar steps on February 1 and February 2 by addition of NaCl. The treatments applied are designated by the number pairs 0-0 (control), 0-4 (split root), and 4-4 (high salt), where the paired numbers indicate the absolute value of the decrease in osmotic potential in bars by salination of each half of the 1 Published with the permission of the Director of the University of Wisconsin Agricultural Experiment Station. root system. Nutrient solution only was the 0-0 treatment. When salination of the beans was begun, the first trifoliolate leaves were beginning to expand. Barley plants were salinized in two-7.5-bar steps on February 1 and February 2. The treatments applied were 0-0 (control), 0-15 (split root), and 15-15 (high salt). When salination of the barley was begun, the plants were about 25 cm tall. Barley roots were not rotated between the two solutions, as in the previous experiment (4). There were seven replicate bean plants and seven replicate barley plants for each of the three treatments. Three bean plants and three barley plants, one from each treatment, were harvested at intervals during the experiment to obtain dry weight measurements. Water potential, osmotic potential, and stomatal conductance values reported are for the three bean plants and the three barley plants which were not harvested until the last day of the experiment. Plants harvested prior to this time had values similar to those for the three bean or barley plants reported. RESULTS Figure 1 shows the stomatal conductance of the first tri-foliolate leaf of bean plants and Figure 2 the stomatal con-ductance of the second unfurled leaf of barley. Stomatal con-ductance was measured between 0900 and 1100 hr. Stomatal 0.6 0.5-ai Ln