Search results

There is increasing evidence that the circadian clock is a signif- icant driver of photosynthesis that becomes apparent when environmental cues are experimentally held constant. We studied whether the composition of photosynthetic pigments is under circadian regulation, and whether pigment oscillations lead to rhythmic changes in photochemical efficiency. To address these questions, we maintained canopies of bean and cotton, after an entrainment phase, under constant (light or darkness) conditions for 30–48 h. Photosynthesis and quantum yield peaked at subjective noon, and non-photochemical quenching peaked at night. These oscillations were not associ- ated with parallel changes in carbohydrate content or xantho- phyll cycle activity. W e observed robust oscillations of Chl a/b during constant light in both species, and also under constant darkness in bean, peaking when it would have been night dur- ing the entrainment (subjective nights). These oscillations could be attributed to the synthesis and/or degradation of tri- meric light-harvesting complex II (reflected by the rhythmic changes in Chl a/b), with the antenna size minimal at night and maximal around subjective noon. Considering together the oscillations of pigments and photochemistry, the observed pattern of changes is counterintuitive if we assume that the plant strategy is to avoid photodamage, but consistent with a strategy where non-stressed plants maximize photosynthesis. ; The authors acknowledge the support of the following re- search grants: UPV/EHU-GV IT-624-13 and IT-1018-16 from the Basque Government and CTM2014-53902-C2-2-P from the Spanish Ministry of Economy and Competitiveness (MINECO) and the ERDF (FEDER). This study benefited from the CNRS human and technical resources allocated to the Ecotrons Research Infrastructures as well as from the state allocation 'Investissement d'Avenir' ANR-11-INBS- 0001, ExpeER FP7 Transnational Access programme, Ramón y Cajal fellowships (RYC-2012-10970 to V.R.D. and RYC-2008-02050 to J.P.F.), the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR) and internal grants from UWS- HIE to V.R.D. and ZALF to A.G. EHU postdoctora ellowship and JdC-Incorporation fellowship (IJCI-2014- 22489) to B.F.M. are also acknowledged. We remain indebted to E. Gerardeau, D. Dessauw, J. Jean, P. Prudent (Aïda CIRAD), J.-J. Drevon, C. Pernot (Eco&Sol INRA), B. Buatois, A. Rocheteau (CEFE CNRS), S. Devidal, C. Piel, O. Ravel and the full Ecotron team, J. del Castillo, P. Martín, A. Mokhtar, A. Pra, S. Salekin (UdL), S. García-Muñoz (IMIDRA), Z. Kayler and K. Pirhofer-Walzl (ZALF) for out- standing technical assistance during experiment setup, plant cultivation or subsequent measurements.

Molecular clocks drive oscillations in leaf photosynthesis, stomatal conductance, and other cell and leaf-level processes over ~24 h under controlled laboratory conditions. The influence of such circadian regulation over whole-canopy fluxes remains uncertain; diurnal CO2 and H2O vapor flux dynamics in the field are currently interpreted as resulting almost exclusively from direct physiological responses to variations in light, temperature and other environmental factors. We tested whether circadian regulation would affect plant and canopy gas exchange at the Montpellier European Ecotron. Canopy and leaf-level fluxes were constantly monitored under field-like environmental conditions, and under constant environmental conditions (no variation in temperature, radiation, or other environmental cues). ; This study benefited from the CNRS human and technical resources allocated to the Research Infrastructure Ecotrons, as well as from the state allocation 'Investissement d'Avenir' ANR-11-INBS-0001; ExpeER Transnational Access program; Ramón y Cajal fellowships (RYC-2012-10970 to VRD and RYC-2008-02050 to JPF); the Erasmus Mundus Master Course Mediterranean Forestry and Natural Resources Management (MEDfOR); and internal grants from the Leibniz Centre for Agricultural Landscape Research to AG, and from the Western Sydney University's Hawkesbury Institute for the Environment and the Spanish Government (AGL2015-69151-R) to VRD.