Abstract
BackgroundMolecular 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).ResultsWe show direct experimental evidence at canopy scales of the circadian regulation of daytime gas exchange: 20–79 % of the daily variation range in CO2 and 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.ConclusionsOur results show that circadian controls affect diurnal CO2 and 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13742-016-0149-y) contains supplementary material, which is available to authorized users.
Highlights
Terrestrial ecosystems play a major role in the global carbon and water cycles
We entrained the bean and cotton canopies for 5 days under average daily patterns of air temperature (Tair) and vapour pressure deficit (VPD) for an August day in Montpellier, albeit with lower photosynthetically active radiation (PAR, up to 500 μmol m-2 s-1, Fig. 1 E-F)
Diurnal variation during the entrainment phases would have been largely attributed to direct environmental effects of PAR, Tair and VPD on physiological processes (Sellers et al, 1997; Hollinger et al, 1994; Richardson et al, 2007; Jones, 2014; Schwalm et al, 2010)
Summary
Terrestrial ecosystems play a major role in the global carbon and water cycles. It is currently estimated that ~30% of fossil fuel emissions are sequestered by land (Canadell et al, 2007), and that ~60% of annual precipitation is returned to the atmosphere through evapotranspiration, a flux largely dominated by transpiration (Schlesinger and Jasechko, 2014). A significantly smaller body of research has sought to disentangle whether, apart from responses to exogenous factors, endogenous processes could play a role (Resco et al., 2009). It has been documented, for instance, how for a given level of water potential and concentration of abscisic acid (ABA), stomatal conductance is higher in the morning than in the afternoon (Mencuccini et al, 2000). There are additional processes creating endogenous flux variation, but only the circadian clock will be addressed here
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
