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| Titel |
Carbon Isotope Discrimination in Leaves of C3 Plants |
| VerfasserIn |
M. Cuntz, G. Gleixner |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028434
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| Zusammenfassung |
| Carbon isotope composition is regarded as a powerful tool in understanding carbon cycling,
both as a tracer and as a process recorder. However, accurate predictions of, for example,
partitioning the net carbon flux into its components or obtaining climate information from
tree rings, requires a good understanding of plant metabolism and related isotopic
fractionations. Mechanistic models have concentrated largely on photosynthetic pathways
and their isotopic composition. This cannot be said for respiratory processes. The mechanistic
models of leaf isotope discrimination hence do not describe dawn, dusk and night
very realistically or not at all. A new steady-state approach of the carbon isotope
distribution in glucose potentially addresses the time of twilight and night (Tcherkez et al.
2004).
Here, a new model of 13C discrimination in leaves of C3 plants is presented. The model is
based on the steady-state approach of Tcherkez et al. (2004) but with much reduced
complexity while retaining its general characteristics. In addition, the model introduces some
new concepts such as a day-length dependent starch synthesis, night-length dependent starch
degradation, energy-driven biosynthesis rates, and continuous leaf discrimination calculation
for the whole diel cycle. It is therefore well adapted for biosphere-atmosphere exchange
studies.
The model predicts enriched sucrose and starch pools in the leaf compared to assimilated
CO2. Biosynthesis on the other hand acts as the sink of the remaining, depleted carbon. The
model calculates slightly different absolute starch compositions from the Tcherkez et al.
(2004) model but this depends on chosen fractionation factors. The greatest difference
between the two models is during dawn, dusk and night. For example, while Tcherkez et al.
has changing phloem sucrose isotope composition during night, the model here predicts
constant sucrose export composition. Observations seem to support rather constant
phloem isotope composition but no adequate assessment is possible based on current
data.
References
Tcherkez G., Farquhar G.D., Badeck F.-W. & Ghashghaie J. (2004) Theoretical considerations about carbon isotope
distribution in glucose of C3 plants, Functional Plant Biology 31, 857-877 |
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