Natural Variation of Circadian Rhythms in Kalanchoe Species

Plants have evolved an internal body clock — the circadian system — that allows the optimization of behavior during the day by anticipating regular environmental change. This timing mechanism also serves as an internal reference to control flowering time. One observable consequence of the circadian system is the rhythmic regulation of processes that underlie photosynthesis, which persists after plants are transferred to constant conditions. Many cacti and succulents use Crassulacean Acid Metabolism (CAM) as a modification of the predominant C3 method of photosynthesis to limit water loss. CAM allows the temporal separation of carbon capture from the atmosphere and the Calvin-Benson cycle, and so separates stomatal opening from some of the biochemical aspects of photosynthesis. Here we document the diversity of circadian rhythms in several Kalanchoe species and reveal differences in the period, phase and amplitude of circadian outputs derived from regulation of the photosynthetic apparatus.