Limitation of net CO2 assimilation rate by internal resistances to CO2 transfer in the leaves of two tree species (Fagus sylvatica L. and Castanea sativa Mill.)

Abstract

Using a combination of gas‐exchange and chlorophyll fluorescence measurements, low apparent CO 2/O 2 specificity factors (1300 mol mol−1) were estimated for the leaves of two deciduous tree species (Fagus sylvatica and Castanea sativa). These low values contrasted with those estimated for two herbaceous species and were ascribed to a drop in the CO 2 mole fraction between the intercellular airspace (C i) and the catalytic site of Rubisco (C c) due to internal resistances to CO 2 transfer. C c. was calculated assuming a specificity of Rubisco value of 2560 mol mol−1. The drop between C i and C c was used to calculate the internal conductance for CO 2 (g i). A good correlation between mean values of net CO 2 assimilation rate (A) and g i was observed within a set of data obtained using 13 woody plant species, including our own data. We report that the relative limitation of A, which can be ascribed to internal resistances to CO 2 transfer, was 24–30%. High internal resistances to CO 2 transfer may explain the low apparent maximal rates of carboxylation and electron transport of some woody plant species calculated from A/C i curves.