Figure 1

The response of net photosynthesis ( A ) to intercellular CO ₂ concentration ( C _i ) at three different irradiances ( Q = 400, 200 and 50 μmol m⁻² s⁻¹, 400–700 nm) for a representative foliage sample. Linear relationships between A and C_i were fitted for each Q level and their intersections averaged to yield a point which when projected to the A axis was taken as the rate of day respiration (R_d^*) and when projected to the C_i axis was taken as the intercellular CO₂ compensation concentration in the absence of day respiration (C_i^*). The mitochondrial CO₂ compensation concentration (Γ^*) was calculated as Γ^* = C_i^* + R_d^* / g_m (von Caemmerer [2000]), where g_m is mesophyll conductance to CO₂ transfer. Method originally proposed by Laisk, A. (von Caemmerer [2000]) to determine C_i^* and R_d. This figure is equivalent to the one presented by De Lucia et al. ([2003]) but with data drawn from this study.