Response of stomatal conductance to light in tobacco plants

Stomata regulates key plant processes, inluding CO₂ assimilation and water use. Although stomatal conductance models evaluate stomatal regulation by plant leaves, model fits have been often different from research and environmental factors. To compare the applicability of stomatal conductance models in tobacco plants, light-response curves of stomatal conductance were measured in this study. The field study was conducted under controlled CO₂ concentration and temperature using the Li-6400 photosynthesis determination system. CO₂ concentration was maintained at 390 μmol·mol^-1 under different temperatures of 20 ℃, 25 ℃, 30 ℃ and 35 ℃. Stomatal conductance of tobacco across the temperature treatments were fitted with the Ball-Berry model (BB model) and subsequent refinements made by Leuning correction model (BBL model), as well as a mechanism model deduced by Ye Zipiao and Yu Qiang (BBY model). The fitting effects eventually compared. The stomatal conductance model and the emendatory light response model of net photosynthesis were coupled (coupling model) to study the light response characteristics of tobacco stomatal conductance. The results were compared with that from Jarvis model. The fitting results showed that compared with the BB and BBL models, the BBY model better described the relationship between stomatal conductance and net photosynthesis of tobacco across the temperature treatments. Both the coupling and Jarvis models well fitted the response of stomatal conductance to light. However, the fitting effects of the coupling model were better, which directly estimated the maximum stomatal conductance along with the corresponding saturation light intensity. Also the coupling model could be used to study the extent of synchronization of maximum stomatal conductance and net photosynthetic rate. The study showed no synchronization of maximum stomatal conductance and maximum net photosynthetic rate of tobacco across the temperature treatments. At 20 ℃, tobacco stomatal conductance reached the maximum value earlier than net photosynthetic rate. At other temperature treatments, however, tobacco stomatal conductance reached the maximum value later than net photosynthetic rate.