Stomatal conductance of lettuce grown under or exposed to different light qualities

Background and Aims The objective of this research was to examine the effects of differences in light spectrum on the stomatal conductance (G(s)) and dry matter production of lettuce plants grown Under a day/night cycle with different spectra, and also the effects on G(s) of short-term exposure to different spectra. Methods Lettuce (Lactuca sativa) plants were grown with 6 It dark and 18 h light under four different spectra, red-blue (RB), red-blue-green (RBG), green (GF) and white (CWF), and G(s) and plant growth were measured. Key Results and Conclusions Conductance of plants grown for 23 d under CWF rose rapidly on illumination to a maximum in the middle of the light period, then decreased again before the dark period when it was minimal. However, the maximum was smaller in plants grown under RB, RGB and GF. This demonstrates that spectral quality during growth affects the diurnal pattern of stomatal conductance. Although G(s) was smaller in plants grown under RGB than CWF, dry mass accumulation was greater, suggesting that G(s) did not limit carbon assimilation under these spectral conditions. Temporarily changing the spectral quality of the plants grown for 23 d under CWF, affected stomatal responses reversibly, confirming studies on epidermal strips. This study provides new information showing that G(s) is responsive to spectral quality during growth and, in the short-term, is not directly coupled to dry matter accumulation. (C) 2004 Annals of Botany Company.