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| Titel |
Modeling stomatal conductance in the earth system: linking leaf water-use efficiency and water transport along the soil–plant–atmosphere continuum |
| VerfasserIn |
G. B. Bonan, M. Williams, R. A. Fisher, K. W. Oleson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 5 ; Nr. 7, no. 5 (2014-09-30), S.2193-2222 |
| Datensatznummer |
250115729
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| Publikation (Nr.) |
 copernicus.org/gmd-7-2193-2014.pdf |
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| Zusammenfassung |
| The Ball–Berry stomatal conductance model is commonly
used in earth system models to simulate biotic regulation of
evapotranspiration. However, the dependence of stomatal conductance
(gs)
on vapor pressure deficit (Ds) and soil moisture must be
empirically parameterized. We evaluated the Ball–Berry model used in the
Community Land Model version 4.5 (CLM4.5) and an alternative stomatal
conductance model that links leaf gas exchange, plant hydraulic constraints,
and the soil–plant–atmosphere continuum (SPA). The SPA model simulates
stomatal conductance numerically by (1) optimizing photosynthetic carbon gain
per unit water loss while (2) constraining stomatal opening to prevent leaf
water potential from dropping below a critical minimum. We evaluated two
optimization algorithms: intrinsic water-use efficiency (ΔAn
/Δgs, the marginal carbon gain of stomatal opening) and
water-use efficiency (ΔAn /ΔEl, the
marginal carbon gain of transpiration water loss). We implemented the
stomatal models in a multi-layer plant canopy model to resolve profiles of
gas exchange, leaf water potential, and plant hydraulics within the canopy,
and evaluated the simulations using leaf analyses, eddy covariance fluxes at
six forest sites, and parameter sensitivity analyses. The primary differences
among stomatal models relate to soil moisture stress and vapor pressure
deficit responses. Without soil moisture stress, the performance of the SPA
stomatal model was comparable to or slightly better than the CLM Ball–Berry
model in flux tower simulations, but was significantly better than the CLM
Ball–Berry model when there was soil moisture stress. Functional dependence
of gs on soil moisture emerged from water flow along the
soil-to-leaf pathway rather than being imposed a priori, as in the CLM
Ball–Berry model. Similar functional dependence of gs on
Ds emerged from the ΔAn/ΔEl
optimization, but not the ΔAn /gs
optimization. Two parameters (stomatal efficiency and root hydraulic
conductivity) minimized errors with the SPA stomatal model. The critical
stomatal efficiency for optimization (ι) gave results consistent with
relationships between maximum An and gs seen in leaf
trait data sets and is related to the slope (g1) of the Ball–Berry
model. Root hydraulic conductivity (Rr*) was consistent
with estimates from literature surveys. The two central concepts embodied in
the SPA stomatal model, that plants account for both water-use efficiency and
for hydraulic safety in regulating stomatal conductance, imply a notion of
optimal plant strategies and provide testable model hypotheses, rather than
empirical descriptions of plant behavior. |
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