Coordination between leaf CO₂ diffusion and Rubisco properties allows maximizing photosynthetic efficiency in...

High photosynthetic efficiency intrinsically demands tight coordination between traits related to CO₂ diffusion capacity and leaf biochemistry. Although this coordination constitutes the basis of existing mathematical models of leaf photosynthesis, it has been barely explored among closely related species, which could reveal rapid adaptation clues in the recent past. With this aim, we characterized the photosynthetic capacity of 12 species of Limonium, possessing contrasting Rubisco catalytic properties, grown under optimal (WW) and extreme drought conditions (WD). The availability of CO₂ at the site of carboxylation (C_c ) determined the photosynthetic capacity of Limonium under WD, while both diffusional and biochemical components governed the photosynthetic performance under WW. The variation in the in vivo caboxylation efficiency correlated with both the concentration of active Rubisco sites and the in vitro-based properties of Rubisco, such as the maximum carboxylase turnover rate (k_cat^c ) and the Michaelis-Menten constant for CO₂ (K_c ). Notably, the results confirmed the hypothesis of coordination between the CO₂ offer and demand functions of photosynthesis: those Limonium species with high total leaf conductance to CO₂ have evolved towards increased velocity (i.e. higher k_cat^c ), at the penalty of lower affinity for CO₂ (i.e. lower specificity factor, S_c/o ).