Quantum yields for uptake of carbon dioxide in C₃ vascular plants of contrasting habitats and taxonomic groupings

The maximum quantum yields (φ{symbol}_a,c) for CO₂ uptake in low-oxygen atmospheres were determined for 11 species of C₃ vascular plants of diverse taxa, habitat and life form using an Ulbricht-sphere leaf chamber. Comparisons were also made between tissues of varied age within species. The species examined were Psilotum nudum (L.) P. Beauv., Davallia bullata Wall. ex Hook., Cycas revoluta Thunb., Araucaria heterophylla (Salisb.) Franco, Picea abies (L.) Karst., Nerium oleander L., Ruellia humilis Nutt., Pilea microphylla (L.) Karst., Beaucarnea stricta Lem., Oplismenus hirtellus (L.) P. Beauv. and Poa annua L. Quantum yields were calculated from the initial slopes of the response of CO₂ uptake to the quantity of photons absorbed in conditions of diffuse lighting. Regression analysis of variance of the initial slopes of the response of CO₂ uptake to photon absorption failed to show any statistically significant differences between age classes within species or between the mature photosynthetic organs of different species. The constancy of φ{symbol}_a,c was apparent despite marked variation in the light-saturated rates of CO₂ uptake within and between species. The mean φ{symbol}_a,c was 0.093±0.003 for 11 species. By contrast, surface absorptance varied markedly between species from 0.90 to 0.60, producing proportional variation in the quantum yield calculated on an incidentlight basis. The ratio of variable to maximum fluorescence emission at 695 nm for the same tissues also failed to show any statistically significant variation between species, with a mean of 0.838±0.008. Mean values of φ{symbol}_a,c reported here for C₃ species, in the absence of photorespiration, are higher than reported in previous surveys of vascular plants, but consistent with recent estimates of the quantum yields of O₂ evolution.