Figure 6.

(a) Diagram comparing two cell‐type C₄ photosynthesis and a rice leaf with low capacity C₄ photosynthesis occurring around the veins. In the latter, C₃ photosynthesis occurs in all mesophyll cells (rectangular cells) and in bundle sheath cells (cells inside circles), in addition to C₄ photosynthesis occurring only in mesophyll cells adjacent to bundle sheath cells. (b) Modelled CO₂ assimilation rates of a rice leaf with low capacity C₄ photosynthesis occurring around the veins (purple line). Also shown are rice leaf with C₃ photosynthesis (blue line), a standard high capacity C₄ photosynthesis (red line), and the C₄ photosynthesis around the vein contributing to the enhanced photosynthesis rate of the purple line (dark red line). C₃ leaf photosynthesis has been modelled with RuBisCO maximal activity, V_cmax = 90 µmol m⁻² sec⁻¹ and electron transport rate, J = 150 µmol m⁻² sec⁻¹. The standard C₄ photosynthesis was modelled with V_cmax = 40 µmol m⁻² sec⁻¹ and PEP carboxylase maximal activity, V_pmax = 300 µmol m⁻² sec⁻¹. The low capacity C₄ photosynthesis around the veins was modelled with V_cmax = 5 µmol m⁻² sec⁻¹ and V_pmax = 25 µmol m⁻² sec⁻¹. In the combined C₃ and C₄ photosynthesis, the total V_cmax was maintained at 90 µmol m⁻² sec⁻¹. C₃ RuBisCO kinetic constants by von Caemmerer (2000) were used together with the Michaels constant for CO₂ of PEPC of 154 µbar (Boyd et al., 2015).