Calculation of gmax
Total maximum stomatal conductance to water vapor (gmax) was calculated as the sum of the maximum conductance values for adaxial (gmax-ada) and abaxial side (gmax-aba), as given in Taylor et al ., (2012), based on the model of Brown & Escombe (1900) after Franks & Beerling (2009a). The equation used to calculate gmax-adaand gmax-aba is:
\(g_{i}=\frac{d}{v}\bullet D\bullet\frac{a_{\max}}{l+\ \frac{\pi}{2}\bullet\sqrt{\frac{a_{\max}}{\pi}}}\)(Eqn 5)
where,
the subscript gi indicates the maximum stomatal conductance to water vapor for adaxial side (gmax-ada, mol m-2 s-1) or abaxial side (gmax-aba, mol m-2s-1), d (m2s-1) is the diffusivity of water in air at 25oC, \(v\) (m3mol-1) is the molar volume of air at 25oC, D (m-2) is the stomatal density for adaxial or abaxial side, amax is the maximum stomatal pore area predicted from its relationship with stomatal size and l is the depth of stomata assumed to be equal to the guard cell widths. Stomatal density and size were measured as mentioned in previous section.