title: Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration.
abstract: • Photosynthetic carbon (C) isotope discrimination (Δ(Α)) labels photosynthates (δ(A) ) and atmospheric CO(2) (δ(a)) with variable C isotope compositions during fluctuating environmental conditions. In this context, the C isotope composition of respired CO(2) within ecosystems is often hypothesized to vary temporally with Δ(Α). • We investigated the relationship between Δ(Α) and the C isotope signals from stem (δ(W)), soil (δ(S)) and ecosystem (δ(E)) respired CO(2) to environmental fluctuations, using novel tuneable diode laser absorption spectrometer instrumentation in a mature maritime pine forest. • Broad seasonal changes in Δ(Α) were reflected in δ(W,) δ(S) and δ(E). However, respired CO(2) signals had smaller short-term variations than Δ(A) and were offset and delayed by 2-10 d, indicating fractionation and isotopic mixing in a large C pool. Variations in δ(S) did not follow Δ(A) at all times, especially during rainy periods and when there is a strong demand for C allocation above ground. • It is likely that future isotope-enabled vegetation models will need to develop transfer functions that can account for these phenomena in order to interpret and predict the isotopic impact of biosphere gas exchange on the C isotope composition of atmospheric CO(2).
authors.affiliation: School of GeoSciences, University of Edinburgh, Edinburgh, UK. l.wingate@ed.ac.uk
authors.forename: Lisa
authors.initials: L
authors.lastname: Wingate
authors.forename: Jérôme
authors.initials: J
authors.lastname: Ogée
authors.forename: Régis
authors.initials: R
authors.lastname: Burlett
authors.forename: Alexandre
authors.initials: A
authors.lastname: Bosc
authors.forename: Marion
authors.initials: M
authors.lastname: Devaux
authors.forename: John
authors.initials: J
authors.lastname: Grace
authors.forename: Denis
authors.initials: D
authors.lastname: Loustau
authors.forename: Arthur
authors.initials: A
authors.lastname: Gessler
mesh_terms: D000332:Aerobiosis; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D002940:Circadian Rhythm / Q000502:physiology; D017753:Ecosystem; D010788:Photosynthesis / Q000502:physiology*; D018547:Plant Stems / Q000378:metabolism*; D012621:Seasons; D012987:Soil / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon