Carbon Dioxide Assimilation,Transpiration, and Leaf Conductance of Bean (Phaseolus Vulgaris L.) Under Blue and Red Radiation

In bean (Phaseolus vulgaris L.) seedlings well supplied with water, rates of transpiration (E) and CO₂ assimilation (P_N) of the primary leaves were measured under blue (BR) or red (RR) irradiance of 150 µmol(photon) m^–2 s^–1. The leaf conductance to H₂O vapour transfer (g_H2O), as well as the intercellular concentrations of H₂O vapour (e_i) and of CO₂ (C_i) were calculated. Under BR, g_H2O was significantly greater, but P_N was lower, and E similar as compared with corresponding values found under RR. The increase of stomata aperture under BR was evident although C_i was higher and e_i was lower than under RR. Results agree with the suggestion that BR directly activates guard cell metabolism and in well watered plants determines mainly the stomata aperture.