Association of Dark Opening of Stomata with Air Pollution Sensitivity of Irish Potatoes

The magnitude of dark opening of stomata on leaves of Irish potato (Solanum tuberosum L.) Has studied to determine if th is opening was related to the high sensitivity of these plants to air pollutants. Stomatal opening was studied over diurnal periods both in the field and in controlled environments. In both environments, stomatal conductance decreased rapidly at the initiation of dark to 0.1 cm.s(-1) hut then increased to 0.2 cm.s(-1) over the dark period, However conductance was always less in the dark than in the light (0.3 to 0.9 cm.s(-1)). During the early part of the dark period, stomatal conductance in controlled environments was not as great as in the field, but conductance was similar in both environments over the latter part of the dark period. Cultivars Norchip and Kennubec had smaller conductances during the First hours of the dark than Haig or Katahdin, and all cultivars increased in conductance over the dark period. 'Haig' show cd slightly higher conductance than the other three during the last 4 hours of the dark period. Injury to 'Haig' from 3-hour fumigations with sulfur dioxide (SO2) or ozone (O-3) demonstrated that exposures during the day generally produced more injury than during the night, although exposures with SO2 during the last 3 hours of the light period produced similar injury to exposures at the end of the dark period, Thus, although partial opening during the dark mag be permitting some pollution injury, it is concluded that previous published reports of similar opening of stomata on Irish potatoes during the light and dark periods, and equal or greater pollution injury during the dark compared with the light period, were not substantiated and apparently resulted from procedural artifacts.