where Ca is the atmospheric CO2 concentration, R is the apparent
respiration rate, which is assumed to be constant, z is the leaf thickness,
and k is the leaf surface and boundary layer conductance for
CO2 diffusion. In this study, the atmospheric CO2 concentration (Ca)
and leaf thickness (z) are constant for the experimental time. The
value of k depends on the diffusion coefficient of CO2 (D). The value
of D is expressed as