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| Titel |
A kinetic model relating the leaf uptake of carbonyl sulfide (COS) to water and CO2 fluxes and 13C fractionation |
| VerfasserIn |
Ulrike Seibt, Joe Berry, Lisseth Sandoval-Soto, Uwe Kuhn, Jürgen Kesselmeier |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037997
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| Zusammenfassung |
| Carbonyl sulfide (COS) is an atmospheric trace gas that holds great promise for studies of
terrestrial carbon and water exchange. During photosynthesis, COS and CO2 follow the same
pathway and are both taken up in enzyme reactions in leaves. We have developed a simple
model of leaf COS uptake, analogous to the equations for CO2 and water fluxes. Leaf COS
uptake predicted from the new equation was in good agreement with data from
field and laboratory chambers, although with large uncertainties. We also obtained
first estimates for the ratio of conductances of COS and water vapour. Empirically
derived estimates were 2.0 ± 0.3 for laboratory data on Fagus sylvatica and 2.2 ±
0.8 for field data on Quercus agrifolia, both close to the theoretical estimate of
2.0 ± 0.2. As a consequence of the close coupling of leaf COS and CO2 uptake,
the normalized uptake ratio of COS and CO2 can be used to provide estimates
of Ci-Ca, the ratio of intercellular to atmospheric CO2, an important plant gas
exchange parameter that cannot be measured directly. Published normalized COS
to CO2 uptake ratios for leaf studies on a variety of species fall in the range of
1.5 to 4, corresponding to Ci-Ca ratios of 0.5 to 0.8. In addition, we utilize the
coupling of Ci-Ca and photosynthetic 13C discrimination to derive an estimate of 2.8
± 0.3 for the global mean normalized uptake ratio. This corresponds to a global
vegetation sink of COS in the order of 900 ± 100 Gg S yr-1. Similarly, COS and 13C
discrimination can be combined to obtain independent estimates of photosynthesis
(GPP). The new process-oriented description provides a framework for understanding
COS fluxes that should improve the usefulness of atmospheric COS data to obtain
estimates of gross photosynthesis and stomatal conductance at regional to global scales. |
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