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.) was studied to determine if this 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 but 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 Kennebec 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' showed 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 (SO 2) or ozone (O3) demonstrated that exposures during the day generally produced more injury than during the night, although exposures with SO 2 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 may 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. on 15 April 1984, at 30 cm in-row spacing and 90 cm between- row spacing. The field was fertilized with N, P, and K at planting and additional nitrogen at emergence and hilling. Herbicides were used at planting, fungicides were used weekly for blight, and insecticides applied as needed. Overhead irrigation was used. Stomatal data were collected from 11 to 20 June, when plants had four to five branching stems and 9 to 12 leaves over 5 cm in length on each stem. Temperature, irradiance, and humidity were re- corded manually at about 2 h intervals at the field site. During the period of sampling reported in this paper (11 to 12 and 19 to 20