where A is the net photosynthesis rate, gs is the stomatal conductance,
Ca is the CO2 concentration on the external side of a leaf and Ci
is the CO2 concentration on the internal side of a leaf
reported the stomatal conductance theory, in which the stomatal
conductance (gs), expressed by Eq. (4), indicates the CO2 absorption
rate. Note that, if gs is small, plants have difficulty absorbing CO2