Stomata play an important role in uptaking CO2 for photosynthesis while limiting water loss during transpiration. Consequently, an accurate depiction of stomatal conductance is required to study leaf energy fluxes, transpiration, and photosynthesis.
This section describes multiple models of stomatal conductance implemented in ClimaLand.
The Medlyn model is a semiempirical model that relates stomatal conductance and photosynthesis and is derived from water-use efficiency optimization theory.
Transpiration is computed using the stomatal conductance and Monin-Obukhov theory.
where
We also need the effective conductivity, given by
where
The stomatal conductance is calculated using the Medlyn stomatal conductance model (Medlyn, 2011), while omitting cuticular and epidermal losses by assuming zero minimum stomatal conductance:
where
where g1 is the slope parameter, inversely proportional to the square root of marginal water use efficiency (Medlyn, 2011). We also have A$_n$ as the biochemical demand for CO$2$ calculated using the photosynthesis model (Farquhar, 1980; Equation \eqref{eq:a_n}; units of molar flux). The resulting units are $m/s$. $g{0,m}$ is a minimum molar conductivity. (subscript
The model has the following parameters:
Constants | Symbol | Unit | Value |
---|---|---|---|
Relative diffusivity of water vapor | - | 1.6 | |
Minimum stomatal conductance | mol/$m^2$/s | 1e-4 | |
Slope parameter | 790 |