Mesophyll cell properties for some C₃ and C₄ species with high photosynthetic rates

Abstract

Abstract Leaves of twelve C 3 species and six C 4 species were examined to understand better the relationship between mesophyll cell properties and the generally high photosynthetic rates of these plants. The CO 2 diffusion conductance expressed per unit mesophyll cell surface area (g CO2 cell ) cell was determined using measurements of the net rate of CO 2 uptake, water vapor conductance, and the ratio of mesophyll cell surface area to leaf surface area (A mes /A). A mes /A averaged 31 for the C 3 species and 16 for the C 4 species. For the C 3 species g CO2 cell ranged from 0.12 to 0.32 mm s ‐1 , and for the C 4 species it ranged from 0.55 to 1.5 mm s ‐1 , exceeding a previously predicted maximum of 0.5 mm s ‐1 . Although the C 3 species Cammissonia claviformis did not have the highest g CO2 cell , the combination of the highest A mes and highest stomatal conductance resulted in this species having the greatest maximum rate of CO 2 uptake in low oxygen, 93 μmol m ‐2 s ‐1 (147 mg dm ‐2 h ‐1 ). The high g CO2 cell of the C 4 species Amaranthus retroflexus (1.5 mm s ‐1 ) was in part attributable to its thin cell wall (72 nm thick).