Minimum epidermal conductance – gmin (mmol � m-2 � s-1)
The gmin is the conductance to vapor diffusion across the epidermis once stomata are closed, i.e., through the cuticle and any leaky stomata. The gmin varies many-fold across species, and can be a potentially strong determinant of drought tolerance, since a lower gmin better enables maintenance of hydration based on stored water.
The gmin is calculated as the difference in leaf mass for a given drying interval divided by the vapor pressure driving force for diffusion of vapor pressure out of the leaf, normalized by leaf area. Alternatively, gmin is calculated as the slope of leaf mass vs time during drying divided by the average mole fraction driving force over the interval, normalized by leaf area.
Note that by convention for gmin, the area of both leaf surfaces is used.