title: Carbon isotope discrimination during branch photosynthesis of Fagus sylvatica: a Bayesian modelling approach.
abstract: Field measurements of photosynthetic carbon isotope discrimination ((13)Δ) of Fagus sylvatica, conducted with branch bags and laser spectrometry, revealed a high variability of (13)Δ, both on diurnal and day-to-day timescales. We tested the prediction capability of three versions of a commonly used model for (13)Δ [called here comprehensive ((13)(Δcomp)), simplified ((13) Δsimple) and revised ((13)(Δrevised)) versions]. A Bayesian approach was used to calibrate major model parameters. Constrained estimates were found for the fractionation during CO(2) fixation in (13)(Δcomp), but not in (13)(Δsimple), and partially for the mesophyll conductance for CO(2)(gi). No constrained estimates were found for fractionations during mitochondrial and photorespiration, and for a diurnally variable apparent fractionation between current assimilates and mitochondrial respiration, specific to (13)(Δrevised). A quantification of parameter estimation uncertainties and interdependencies further helped explore model structure and behaviour. We found that (13)(Δcomp) usually outperformed (13)(Δsimple) because of the explicit consideration of gi and the photorespiratory fractionation in (13)(Δcomp) that enabled a better description of the large observed diurnal variation (≈9‰) of (13)Δ. Flux-weighted daily means of (13)Δ were also better predicted with (13)(Δcomp) than with (13)(Δsimple).
authors.affiliation: Institute of Agricultural Sciences, ETH Zurich, Universitätsstrasse 2, Zurich, 8092, Switzerland; UR1263 Ephyse, INRA, Villenave d'Ornon, 33140, France.
authors.forename: Lydia
authors.initials: L
authors.lastname: Gentsch
authors.forename: Albin
authors.initials: A
authors.lastname: Hammerle
authors.forename: Patrick
authors.initials: P
authors.lastname: Sturm
authors.forename: Jérôme
authors.initials: J
authors.lastname: Ogée
authors.forename: Lisa
authors.initials: L
authors.lastname: Wingate
authors.forename: Rolf
authors.initials: R
authors.lastname: Siegwolf
authors.forename: Peter
authors.initials: P
authors.lastname: Plüss
authors.forename: Thomas
authors.initials: T
authors.lastname: Baur
authors.forename: Nina
authors.initials: N
authors.lastname: Buchmann
authors.forename: Alexander
authors.initials: A
authors.lastname: Knohl
mesh_terms: D001499:Bayes Theorem; D002138:Calibration; D002247:Carbon Isotopes; D002940:Circadian Rhythm / Q000502:physiology; D019992:Databases as Topic; D029964:Fagus / Q000502:physiology*; D008954:Models, Biological; D010788:Photosynthesis; D013557:Switzerland; D013696:Temperature; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes
keywords: Farquhar model; gas exchange; isotopologues; laser spectrometer; open branch bags; photosynthetic 13C discrimination