Aftereffects of Low and High Temperature Pretreatment on Leaf Resistance, Transpiration, and Leaf Temperature in Xanthium1


Leaf resistance for water vapor (total diffusion resistance minus boundary layer resistance), transpiration, and leaf temperature were measured in attached leaves of greenhouse-grown Xanthium strumarium L. plants that had been pretreated for 72 hours with high (40 C day, 35 C night), or low (10 C day, 5 C night) air temperatures. Measurements were made in a wind tunnel at light intensity of 1.15 cal cm−2 min−1, air temperatures between 5 and 45 C, and wind speed of 65 cm sec−1. Leaf resistances in low temperature pretreated plants were higher (8 to 27 sec cm−1) than in controls or high temperature pretreated plants (0.5 to 3 sec cm−1) at leaf temperatures between 5 and 25 C. Thus, the pretreatment influenced stomatal aperture.

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