Research Program Area: Ecosystem & Multimedia Effects
Topic Areas: Ecosystem Impacts
The interaction between photochemical oxidants (primarily O3) and salinity on vegetation was evaluated in the field. Alfalfa, an important crop grown in the Sacramento and San Joaquin Valleys and Southern California was the test plant. Two cultivars, one salinity resistant "U.C. Salton," but of unknown O3 sensitivity, and a second salinity sensitive and moderately sensitive to O3 "Moapa," were grown at three salinity levels in soil plots at the U.S.D.A. Salinity Laboratory, Riverside, California. Salinity treatments were imposed by irrigating with waters having electrical conductivities (EC) of 0.7, 3 and 6 dS m-1 which resulted in saturated-soil-extract conductivities (ECe) of approximately 1.9, 6.2 and 9.3 dS m-1, respectively, to evaluate the effects of excess salinity in the absence or presence of O3, plants were exposed in open-top chambers to filtered or unfiltered air at ambient O3 concentrations continuously over approximately four and one-half months from July through mid-November, 1985. Important physiological measurements including net photosynthesis, stomatal conductance, water potential, and tissue elemental content, were made to determine the metabolic basis for the salinity-03 interaction. The dry matter production and distribution within the plants were evaluated at four harvests by measuring fresh weight, dry weight, number of nodes per stem, number of empty nodes per stem, and height.
There was no overall significant interaction between ambient O3 and salinity. There was little effect of O3itself on growth, yield, or physiology; only on leaf injury as measured as percent empty nodes for three of the four harvests. For two of these harvests, leaf injury occurred to the same extent in ambient and filtered chambers regardless of the salinity level; for the other harvest injury was reduced with increasing salinity. Salinity was much more detrimental than O3 in affecting plants, causing occasional reductions in fresh weight, dry weight, increased percent dry weight, decreased percent empty nodes, decreased height, decreased photosynthetic rates, more negative stem water pressure potential, and altered elemental content. There were large differences in growth and yield between the two cultivars. A large difference in alfalfa growth and physiology appeared to develop between chambers and outside plots as the growing season progressed. Outside plants tended to have higher fresh and dry weights, a higher percent dry weight, were shorter, had fewer empty nodes, and altered elemental content compared to ambient chamber plants. Overall this study indicated that salinity can reduce O3 injury to plants, but that there was little interaction between O3 and salinity on plant growth, yield, or physiology. At the levels tested, salinity would affect plants much more than O3in areas where both stresses occur. Experimental designs which use open-top chambers to evaluate air pollution x other environmental stress interactions may not adequately represent field conditions due to complex interactions between the chambers themselves and the stresses.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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