Night and day - Circadian regulation of night-time dark respiration and light-enhanced dark respiration in plant leaves and canopies

Abstract The potential of the vegetation to sequester C is determined by the balance between assimilation and respiration. Respiration is under environmental and substrate-driven control, but the circadian clock might also contribute. To assess circadian control on night-time dark respiration (R D ) and on light enhanced dark respiration (LEDR) – the latter providing information on the metabolic reorganization in the leaf during light-dark transitions – we performed experiments in macrocosms hosting canopies of bean and cotton. Under constant darkness (plus constant air temperature and air humidity), we tested whether circadian regulation of R D scaled from leaf to canopy respiration. Under constant light (plus constant air temperature and air humidity), we assessed the potential for leaf-level circadian regulation of LEDR. There was a clear circadian oscillation of leaf-level R D in both species and circadian patterns scaled to the canopy. LEDR was under circadian control in cotton, but not in bean indicating species-specific controls. The circadian rhythm of LEDR in cotton might indicate variable suppression of the normal cyclic function of the tricarboxylic-acid-cycle in the light. Since circadian regulation is assumed to act as an adaptive memory to adjust plant metabolism based on environmental conditions from previous days, circadian control of R D may help to explain temporal variability of ecosystem respiration.