Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration.
• 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).
Wingate
Lisa
L
School of GeoSciences, University of Edinburgh, Edinburgh, UK. l.wingate@ed.ac.uk
Ogée
Jérôme
J
Burlett
Régis
R
Bosc
Alexandre
A
Devaux
Marion
M
Grace
John
J
Loustau
Denis
D
Gessler
Arthur
A
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*
D002247:Carbon Isotopes; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon