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Salinity-Ozone Interactions on Pinto Bean: Integrated Response to Ozone Concentration and Duration¹

ABSTRACT

This investigation was conducted to determine the integrated effects of concentration and duration of ozone exposure on the injury, growth, and mineral composition of pinto bean (Phaseolus vulgaris L.) during rapid vegetative growth and to evaluate the interactive effects of salinity.

Plants were grown in controlled environment chambers in non-saline and two saline nutrients solution cultures having osmotic potentials of –0.4, –2.4, and –4.4 bars, respectively. Ozone-free plants were compared with plants treated daily for 2 weeks with ozone doses of from 0.15 to 0.90 ppm-hour.

Plant injury and reduction in growth were sigmoidal functions of ozone dose. Plant tolerance thresholds were found for both concentration and duration of ozone exposure. Daily exposures above threshold levels produced cumulative injury that progressed from the primary leaves to subsequent trifoliate leaves. Although salinity suppressed plant growth, it extended the tolerance threshold for duration of ozone exposure and significantly reduced the injury by ozone. Ozone decreased Ca, Mg, K, and N contents of the leaves, increased stem contents of these elements, and had relatively little effect on root contents. However, no serious nutritional imbalances were observed.

Key Words: plant growth • leaf ozone injury • plant mineral composition • oxidant • air pollution • osmotic potential

¹ Contribution from the U. S. Salinity Laboratory, Western Region, ARS, USDA, P. O. Box 672, Riverside, Calif. 92502.

² Plant Physiologist, Agricultural Engineer, Supervisory Soil Scientist, and Soil Scientist, respectively.

Received for publication September 7, 1972.