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| Titel |
Leaf oxygen isotope exchange in water vapor and carbon dioxide of Fagus sylvatica under field conditions |
| VerfasserIn |
A. Hammerle, L. Gentsch, M. Barthel, R. Siegwolf, P. Sturm, A. Knohl |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069422
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| Zusammenfassung |
| The stable isotope 18O in water and carbon dioxide is a powerful tracer to investigate
ecological processes, such as the coupled carbon-water cycle and can provide a constraint on
the contribution of terrestrial ecosystems to the global carbon and water cycles. Recently,
laser spectroscopic techniques for isotope measurements have been developed which allow
for field deployable, high accuracy and high frequency measurements of these isotopic
gas-exchanges with the atmosphere.
Here we present a unique dataset of δ18O of water vapor fluxes as well as carbon dioxide
fluxes during leaf gas-exchange, measured simultaneously by two laser spectrometers
under field conditions, using steady-state through-flow branch chambers. The study
was conducted on beech trees (n=3) in a mixed-deciduous forest in Switzerland in
2010.
The effective path-length (L), an important parameter in respect to leaf water enrichment,
was constrained by using a Bayesian inversion scheme in combination with the
Péclet-modified Craig Gordon model and frequently taken leaf water samples. Using the
determined value of L, modeled 18O values of leaves inside the chambers were compared
with values derived from the branch chamber transpiration measurements. The good
agreement between these two approaches implies a very good performance of the chamber
system in measuring isotopic gas-exchange of water. Given this validation of the measured
leaf water enrichment values in 18O, carbonic anhydrase efficiency was calculated from
these leaf water enrichment values and the measured apparent “discrimination” of
C18OO. Our results support the few recent findings of other groups, that carbonic
anhydrase efficiency measured under field conditions is lower compared to lab derived
values.
In summary, this study provides (i) a Bayesian inversion scheme to estimate L of beech
leaves, (ii) a long dataset of parallel measurements of 18O in water vapor and carbon dioxide
gas exchange measured on branch level under field conditions and (iii) an estimate of the
carbonic anhydrase efficiency of beech trees. |
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