Implementation and evaluation of the unified stomatal optimization approach in the Functionally Assembled Terrestrial Ecosystem Simulator (FATES)
<p>Stomata play a central role in regulating the exchange of carbon dioxide and water vapor between ecosystems and the atmosphere. Their function is represented in land surface models (LSMs) by conductance models. The Functionally Assembled Terrestrial Ecosystem Simulator (FATES) is a dynamic...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-06-01
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| Series: | Geoscientific Model Development |
| Online Access: | https://gmd.copernicus.org/articles/15/4313/2022/gmd-15-4313-2022.pdf |
| Summary: | <p>Stomata play a central role in regulating the exchange of carbon
dioxide and water vapor between ecosystems and the atmosphere. Their
function is represented in land surface models (LSMs) by conductance models.
The Functionally Assembled Terrestrial Ecosystem Simulator (FATES) is a
dynamic vegetation demography model that can simulate both detailed plant
demographic and physiological dynamics. To evaluate the effect of stomatal
conductance model formulation on forest water and carbon fluxes in FATES, we
implemented an optimality-based stomatal conductance model – the Medlyn
(MED) model – that simulates the relationship between photosynthesis (<span class="inline-formula"><i>A</i></span>) and
stomatal conductance to water vapor (<span class="inline-formula"><i>g</i><sub>sw</sub></span>) as an alternative to the FATES
default Ball–Woodrow–Berry (BWB) model. To evaluate how the behavior of
FATES is affected by stomatal model choice, we conducted a model sensitivity
analysis to explore the response of <span class="inline-formula"><i>g</i><sub>sw</sub></span> to climate forcing, including
atmospheric CO<span class="inline-formula"><sub>2</sub></span> concentration, air temperature, radiation, and vapor
pressure deficit in the air (VPD<span class="inline-formula"><sub>a</sub></span>). We found that modeled <span class="inline-formula"><i>g</i><sub>sw</sub></span> values
varied greatly between the BWB and MED formulations due to the different
default stomatal slope parameters (<span class="inline-formula"><i>g</i><sub>1</sub></span>). After harmonizing <span class="inline-formula"><i>g</i><sub>1</sub></span> and
holding the stomatal intercept parameter (<span class="inline-formula"><i>g</i><sub>0</sub></span>) constant for both model
formulations, we found that the divergence in modeled <span class="inline-formula"><i>g</i><sub>sw</sub></span> was limited to
conditions when the VPD<span class="inline-formula"><sub>a</sub></span> exceeded 1.5 kPa. We then evaluated model
simulation results against measurements from a wet evergreen forest in
Panama. Results showed that both the MED and BWB model formulations were
able to capture the magnitude and diurnal changes of measured <span class="inline-formula"><i>g</i><sub>sw</sub></span> and <span class="inline-formula"><i>A</i></span> but underestimated both by about 30 % when the soil was
predicted to be very dry. Comparison of modeled soil water content from
FATES to a reanalysis product showed that FATES captured soil drying well,
but translation of drying soil to modeled physiology reduced the models'
ability to match observations. Our study suggests that the parameterization
of stomatal conductance models and current model response to drought are the
critical areas for improving model simulation of CO<span class="inline-formula"><sub>2</sub></span> and water fluxes
in tropical forests.</p> |
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| ISSN: | 1991-959X 1991-9603 |