© 1991 Heron Publishing—Victoria, Canada
Net CO2 assimilation of cacao seedlings following dark chilling
Robert J. Joly and Daniel T. Hahn
Department of Horticulture, Purdue University, West Lafayette, IN 47907 USA / Received December 27, 1990
Summary
Overnight exposure of cacao (Theobroma cacao L.) seedlings to chilling temperatures between 4.7 and 15.8 °C reduced net CO2 assimilation rate (A) and stomatal conductance to water vapor (gs), with temperatures below 10 °C causing severe inhibition. Net CO2 assimilation rates of chilled seedlings recovered to those of nonchilled plants within 7 days. No differences in daytime
intercellular CO2 concentration (ci) with overnight temperature were observed on the first day after the chilling treatment, which indicates that the reduction
in photosynthesis was not caused by the reduction in stomatal conductance. However, ci of chilled plants was much less than that of nonchilled plants on the second day after treatment, which suggests that chilling
caused a change in stomatal response to CO2 concentration. Even 7 days after treatment, when A had recovered to control values, gs of chilled leaves was only approximately 70% that of controls. Chilling did not inhibit A through an effect on leaf water potential, which was higher in chilled plants than in unchilled plants.
