Leaf Diffusion Resistance, Illuminance, and Transpiration

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Abstract
Stepwise increases in fluorescent illuminance, imposed as a single variable in a controlled environment, induced progressive stomatal opening in 8 plant species, as evidenced by a consistent decrease in leaf diffusion resistance (RL), ranging from 15 to 70 sec cm−1 in darkness to about 1 sec cm−1 at approximately 40 kilolux. The minimum RL values were the same for the upper and the lower epidermis, provided that stomatal density was adequate. Saturation illuminance was not achieved in any species; extrapolation indicates that 50 kilolux would bring about full stomatal opening (RL ≤ 0.1 sec cm−1).