In a 5-months' experiment with white clover grown in two CO2 atmospheres (AC = 350 and EC = 700 cm3 m-3) and two humidities (-0.2 and -0.8 MPa), changes in fluorescence induction parameters were investigated. Changes induced by EC did not coincide with those induced by moderate drought. Long-term EC significantly increased stationary fluorescence Fs and decreased the vitality coefficient Rfd. Moderate drought significantly shortened the fluorescence half-time and decreased the area above the induction curve Sc and the Fv/Fm ratio. and M. Pol, D. Gołębiowska, J. Miklewska.