Comparison of seasonal variations in water-use efficiency calculated from the carbon isotope composition of tree rings and flux data in a temperate forest.
Tree-ring δ(13) C is often interpreted in terms of intrinsic water-use efficiency (WUE) using a carbon isotope discrimination model established at the leaf level. We examined whether intra-ring δ(13) C could be used to assess variations in intrinsic WUE (W(g), the ratio of carbon assimilation and stomatal conductance to water) and variations in ecosystem WUE (W(t) , the ratio of C assimilation and transpiration) at a seasonal scale. Intra-ring δ(13) C was measured in 30- to 60-µm-thick slices in eight oak trees (Quercus petraea). Canopy W(g) was simulated using a physiologically process-based model. High between-tree variability was observed in the seasonal variations of intra-ring δ(13) C. Six trees showed significant positive correlations between W(g) calculated from intra-ring δ(13) C and canopy W(g) averaged over several days during latewood formation. These results suggest that latewood is a seasonal recorder of W(g) trends, with a temporal lag corresponding to the mixing time of sugars in the phloem. These six trees also showed significant negative correlations between photosynthetic discrimination Δ calculated from intra-ring δ(13) C, and ecosystem W(t), during latewood formation. Despite the observed between-tree variability, these results indicate that intra-ring δ(13) C can be used to access seasonal variations in past W(t).
Michelot
Alice
A
Univ Paris-Sud, Laboratoire Ecologie Systématique et Evolution, UMR8079, Orsay, F-91405, France. alice.michelot@u-psud.fr
Eglin
Thomas
T
Dufrêne
Eric
E
Lelarge-Trouverie
Caroline
C
Damesin
Claire
C
D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis; D017753:Ecosystem; D004777:Environment; D008954:Models, Biological; D010788:Photosynthesis; D018526:Plant Transpiration; D029963:Quercus / Q000254:growth & development / Q000378:metabolism* / Q000502:physiology; D012621:Seasons; D013997:Time Factors; D014867:Water / Q000378:metabolism*
D002247:Carbon Isotopes; D014867:Water; D002245:Carbon Dioxide