The Dark Fixation of Carbon Dioxide as a Factor in Photoperiodism

Abstract

Studies were conducted to determine the relationships existing between the fixation of CO2 in the dark and photo-periodic induction in a long-day species, Wintex barley, and in two short-day species, Biloxi soybean and Xanthium commune. Inhibition of floral initiation occurred when soybean and Xanthium plants were exposed to long dark periods in air essentially free of CO2. Similar conditions only slightly inhibited initiation of barley. Photoinduction promoted the fixation of CO2 in the dark in all three species tested. CO2 fixation rates during a long dark period appeared to be different in barley than in Xanthium and soybean. Night interruption treatments promoted a loss of CO2 fixed in the preceding part of the dark period and lowered the rate of CO2 fixation in the following part of the dark period in Xanthium and soybean but not in barley. The fixation of CO2 in the dark is suggested as a specific physiological factor in the photoperiodic induction of the soybean and Xanthium.