STOMATAL-RESISTANCE OF 3 POTATO CULTIVARS AS INFLUENCED BY SOIL-WATERSTATUS, HUMIDITY AND IRRADIANCE

Leaf stomatal resistance varies considerably in response to changes in environmental conditions. Understanding cultivar differences in the r esponse of stomata to these conditions is important for effectively si mulating water-use and growth. In this study the stomatal resistance o f three field grown potato (Solanum tuberosum L.) cultivars Atlantic, Monona and Norchip was observed in response to photosynthetic photon f lux density, leaf to air vapour pressure difference and root zone avai lable soil water. Substantial variation in stomatal resistance was acc ounted for by functions of the environmental variables for both Monona and Norchip. The explained variation for Atlantic was considerably le ss. Light saturation occurred near 500 mu mol m(-2) s(-1). Increasing stomatal resistance above 1000 mu mol m(-2) s(-1) was also observed bu t is likely an artifact of stomatal closure on days in which mid-day l eaf water potentials dropped below critical levels. Although the leaf to air vapour pressure difference was important, the high humidities i n Eastern Canada are presumably insufficient to obtain substantial eff ects. The soil water status was partially linked to the average 1000 h to 1500 h stomatal resistance on clear, sunny days. Significant diffe rences were observed among the cultivars in the response of stomata to changes in the available soil water.