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| Titel |
Modeling Water Flux through Crops based on the Optimum Water Use Hypothesis |
| VerfasserIn |
Atefeh Hosseini, Sebastian Gayler, Wilfried Konrad, Thilo Streck |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087707
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| Publikation (Nr.) |
 EGU/EGU2014-3026.pdf |
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| Zusammenfassung |
| Vegetation models can be used to predict plants response to altering climate conditions.
Stomatal conductance (gs) controls diffusion of CO2 from the atmosphere to the
leaf and water loss through transpiration and allows plants to adjust themselves to
fluctuating environmental conditions. The hypothesis that stomata adapt optimally to
its environment to maximize assimilation (A) for a given amount of water loss
through transpiration (E) was introduced by Cowan and Farquhar (1977). This theory
provides a framework for modeling the interactions between vegetation dynamics and
soil moisture that does not rely on empirical calibration as long as photosynthetic
canopy properties and total amount of water available for transpiration are known.
The current study introduces a new approach to implement optimization theory of
stomatal conductance into a canopy gas exchange model. The adequacy of the new
approach was tested in a real case study by comparing predicted diurnal cycles
of assimilation and transpiration rates as well as variability of soil moisture with
observations at a winter wheat (Triticum aestivum cv.Cubus) field in southwest
Germany. For analyzing the impact of soil texture on stomata regulation, three soil
types were compared in a drying soil simulation scenario. Soil water balance was
calculated from measured precipitation and simulated transpiration using a single
bucket model, where the soil within the root zone was assumed to be homogeneous.
Since the model focused on fully developed vegetation canopies, soil evaporation is
considered negligible. Marginal water use efficiency can be expressed as partial
derivative of assimilation with respect to transpiration (-A--E =λ). Daily values
of λ were determined using the formalism of Lagrangian multipliers. Potential
evapotranspiration (Penman-Monteith) and effective reduction factor of root water
uptake under unfavorable soil moisture conditions were used to estimate amounts of
plant available water per day. The present study shows that the model based on the
optimal water-use hypothesis produced reasonable results for different soil textures
under drying conditions. When water becomes less available, the gradual increase of
λ reflects the differences in soil water retention properties. Moreover, the model
could delineate the diurnal cycle of transpiration and assimilation of winter wheat
during the development stages with higher discrepancies over leaf senescence period. |
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