Figure 2
Graphic description of the constant J method to determine transfer conductance. (a) The rate of net photosynthesis (A; open circles) and photochemical efficiency of photosystem II (ΦPSII; solid triangles) as a function of the intercellular CO2 concentration (Ci) for a representative foliage sample. Solid lines represent a least-squares fit to the A/Ci and ΦPSII/Ci response. Open squares are observed values used to estimate mesophyll conductance (gm). These values are within the portion of the A/Ci response where ΦPSII indicated that electron transport rate was constant. (b) The variance of estimated electron transport rates, J, for different values of gm. Values of J were estimated for each of the four A values indicated as open squares in Figure 2a using the equation given by Harley et al. ([1992]). The gm that minimized the variance of J estimates for this foliage sample was 0.054 mol m−2 s−1 bar−1. This figure is equivalent to the one presented by Harley et al. ([1992]) and De Lucia et al. ([2003]) but with data drawn from this study.