The influence of irradiance and external CO2-concentration on photosynthesis of different tomato genotypes

With 4 genotypes of tomato, irradiance and CO₂-response curves of net photosynthesis were analysed by means of curve fitting. Estimated values of the light compensation point I_c showed small but significant differences between the genotypes, the overall value being in the order of 8 W m^?2. The photochemical efficiency (α_n) and the maximum net photosynthesis per unit leaf area basis (P_nm) reached the highest values for ‘F6 IVT’ (13.3 μg CO₂ J^?1 resp. 0.549 mg CO₂ m^?2 s^?1), the lowest value of α_n with ‘Bonabel’ (9.9 μg CO₂ J^?1), and the lowest value of P_nm with ‘PI 114969’ (0.424 mg CO₂ m^?2 s^?1). The CO₂-compensation point (C_c) was relatively high (177–245 mg m^?3). ‘F6 IVT’ demonstrated the highest value of C_c, the lowest carboxylation efficiency and the highest maximum rate of net photosynthesis. The results clearly demonstrate that the latter genotype requires a much higher external CO₂-concentration than the other genotypes in order to exhibit the highest rate of net photosynthesis.