Compensatory effects of elevated CO2 concentration on the inhibitory effects of high temperature and irradiance on photosynthetic gas exchange in carrots

Abstract

We determined the interactive effects of irradiance, elevated CO 2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3 levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m-2 s-1), 3 leaf chamber temperatures (15, 20, 30°C), and 2 external CO2 concentrations (C a), AC and EC (350 and 750 μmol mol -1, respectively). Rates of net photosynthesis (P N) and transpiration (E) and stomatal conductance (g s ) were measured, along with water use efficiency (WUE) and ratio of internal and external CO 2 concentrations (C i/C a). P N revealed an interactive effect between PAR and C a. As PAR increased so did P N under both C a regimes. The g s showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters. Maximum WUE occurred at 15°C and 1 200 μmol m-2 s - 1 PAR under EC. The C i /C a was influenced independently by temperature and C a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on P N and WUE. © 2007 Institute of Experimental Botany, ASCR.