Responses to different external light rhythms by the circadian rhythm of Crassulacean acid metabolism in Kalanchoe daigremontiana

Abstract

AbstractTime series of net CO2 exchange (JCO2) and leaf conductivity for water vapour (gH2O) were measured and subsequently analysed mathematically in the Crassulacean acid metabolism (CAM) plant Kalanchoe daigremontiana (Hamet et Perrier de la Bâthie) under constant environmental conditions and under imposed external rhythms of lower and higher light intensity. The time series were analysed by Fourier methods and a correlation analysis considering the first time derivatives of JCO2, gH2Oand photosynthetically active photon flux density (PPFD). The ratio of internal to external CO2 (ci/ca) was also considered in the analysis, leading to a discussion of the interaction of stomata and carbon assimilation under periodic stimulation. It is suggested that for stimulation with frequencies close to the endogeneous circadian period, stomatal conductance and carbon assimilation oscillate synchronously, guard‐cell movements trailing behind changes in internal CO2 with a delay of 10–15 min. For stimulation frequencies far shorter than the endogeneous period, this synchrony can be disturbed due to independent responses of stomata and assimilation to light pulses, leading to an arrhythmic gas exchange pattern. These results are discussed in the context of understanding circadian oscillations as the output of a multioscillator, multisignalling pathway system on the organismic and metabolic level.