Effects of temperature variation on the light-response characteristics of tobacco leaf photosynthesis

By using Li-6400 photosynthesis determination system to control leaf chamber temperature, this paper studied the photosynthetic light-response characteristics of middle tobacco leaves at their initial ripening stage at 17, 20, 25, 30, and 35 ℃. With increasing temperature, the net photosynthetic rate (Pn), maximum net photosynthetic rate (Pnmax), initial slope (α), and stomatal conductance (Gs) decreased after an initial increase, with the maximum at 20 ℃, while the Pn was inhibited obviously at 35 ℃ by strong light. The light compensation point (LCP) and dark respiration rate (Rd) increased with increasing temperature, but decreased slightly at 35 ℃, as compared with those at 30 ℃. The light saturation point (LSP) had a variation of ‘down-up-down’ with increasing temperature, being higher at 35 ℃ and 17 ℃. The transpiration rate (Tr) increased but the water use efficiency (WUE) decreased with increasing temperature. However, WUE was higher at 20 ℃ than that at the other temperatures under strong light. It was suggested that the most favorite temperature for tobacco photosynthesis was 20 ℃, at which, the water- and gas regulation capability of stomata was the strongest. High temperature over 30 ℃ would work against tobacco photosynthesis.