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| Titel |
A kinetic analysis of leaf uptake of COS and its relation to transpiration, photosynthesis and carbon isotope fractionation |
| VerfasserIn |
U. Seibt, J. Kesselmeier, L. Sandoval-Soto, U. Kuhn, J. A. Berry |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 1 ; Nr. 7, no. 1 (2010-01-28), S.333-341 |
| Datensatznummer |
250004385
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| Publikation (Nr.) |
 copernicus.org/bg-7-333-2010.pdf |
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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. In leaves, COS follows
the same pathway as CO2 during photosynthesis. Both gases are taken up in
enzyme reactions, making COS and CO2 uptake closely coupled at the leaf
scale. The biological background of leaf COS uptake is a hydrolysis reaction
catalyzed by the enzyme carbonic anhydrase. Based on this, we derive and test
a simple kinetic model of leaf COS uptake, and relate COS to CO2 and water
fluxes at the leaf scale. The equation was found to predict realistic leaf
COS fluxes compared to observations from field and laboratory chambers. We
confirm that COS uptake at the leaf level is directly linked to stomatal
conductance. As a consequence, the ratio of normalized uptake rates (uptake
rates divided by ambient mole fraction) for leaf COS and CO2 fluxes can
provide an estimate of Ci/Ca, the ratio of intercellular to atmospheric
CO2, an important plant gas exchange parameter that cannot be measured
directly. The majority of 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. COS can now be implemented in the same model framework as
CO2 and water vapour. Atmospheric COS measurements can then provide
independent constraints on CO2 and water cycles at ecosystem, regional and
global scales. |
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