title: Circadian rhythms have significant effects on leaf-to-canopy scale gas exchange under field conditions.
abstract: 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 CO2and 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).
  
  
  
  We show direct experimental evidence at canopy scales of the circadian regulation of daytime gas exchange: 20-79 % of the daily variation range in CO2and H2O fluxes occurred under circadian entrainment in canopies of an annual herb (bean) and of a perennial shrub (cotton). We also observed that considering circadian regulation improved performance by 8-17 % in commonly used stomatal conductance models.
  
  
  
  Our results show that circadian controls affect diurnal CO2and H2O flux patterns in entire canopies in field-like conditions, and its consideration significantly improves model performance. Circadian controls act as a 'memory' of the past conditions experienced by the plant, which synchronizes metabolism across entire plant canopies.
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain. v.rescodedios@gmail.com.
authors.forename: Víctor
authors.initials: V
authors.lastname: Resco de Dios
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, Long-term Forest Ecosystem Research, 8903, Birmensdorf, Switzerland.|Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research, 15374, Müncheberg, Germany.
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain.|Departamento de Botánica, Facultad de Ciencias Naturales y Oceanográficas, Universidad de Concepción, Casilla 160-C, Concepción, Chile.
authors.forename: Juan Pedro
authors.initials: JP
authors.lastname: Ferrio
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain.|School of Environmental Sciences, University of Liverpool, Liverpool, L69 3GP, UK.
authors.forename: Josu G
authors.initials: JG
authors.lastname: Alday
authors.affiliation: Institute of Ecology, University of Innsbruck, 6020, Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Bahn
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Jorge
authors.initials: J
authors.lastname: Del Castillo
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Devidal
authors.affiliation: Instituto Madrileño de Investigación y Desarrollo Rural, Agrario y Alimentario, Finca 'El Encín', 28800, Alcalá de Henares, Madrid, Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: García-Muñoz
authors.affiliation: Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research, 15374, Müncheberg, Germany.|USDA Forest Service, Northern Research Station, Lawrence Livermore National Laboratory, Livermore, California, 94550, USA.
authors.forename: Zachary
authors.initials: Z
authors.lastname: Kayler
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Landais
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Martín-Gómez
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.|Centre National de la Recherche Scientifique, Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, Université de Montpellier, Université Paul Valéry, École Pratique des Hautes Études, F-34293, Montpellier Cedex 5, France.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Milcu
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.
authors.forename: Clément
authors.initials: C
authors.lastname: Piel
authors.affiliation: Institute for Landscape Biogeochemistry, Leibniz Centre for Agricultural Landscape Research, 15374, Müncheberg, Germany.|Institut für Biologie, Plant Ecology, Freie Universität Berlin, D-14195, Berlin, Germany.|Berlin-Brandenburg Institute of Advanced Biodiversity Research, D-14195, Berlin, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Pirhofer-Walzl
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Ravel
authors.affiliation: Erasmus Mundus Master on Mediterranean Forestry and Natural Resources Management, Universitat de Lleida, 25198, Lleida, Spain.|School of Forestry, College of Engineering, University of Canterbury, 8140, Christchurch, New Zealand.
authors.forename: Serajis
authors.initials: S
authors.lastname: Salekin
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, 2753, Australia.
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, 2753, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Tjoelker
authors.affiliation: Department of Crop and Forest Sciences Agrotecnico Center, Universitat de Lleida, 25198, Lleida, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Voltas
authors.affiliation: Ecotron Européen de Montpellier, UPS 3248, Centre National de la Recherche Scientifique, Campus Baillarguet, 34980, Montferrier-sur-Lez, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Roy
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis*; D057906:Circadian Clocks; D002940:Circadian Rhythm; D017753:Ecosystem; D003368:Gossypium / Q000502:physiology; D027805:Phaseolus / Q000502:physiology; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D054046:Plant Stomata / Q000378:metabolism; D014867:Water / Q000032:analysis*
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Circadian clock; Ecological memory; Net ecosystem exchange; Photosynthesis; Scaling; Stomatal conductance models; Transpiration