Evaluation of the potential to measure photosynthetic rates in C-3 plants (Flaveria pringlei and Oryza sativa) by combining chlorophyll fluorescence analysis and a stomatal conductance model

The response curves of leaf photosynthesis to varying light, temperature and leaf-to-air vapour pressure deficit were measured in the C-3 plants Flaveria pringlei and Oryza sativa in normal air with a computerized open infrared gas analysis (IRCA) system, and the photochemical efficiency of photosystem II, described as (1-F-s/F'(m)) after Genty, Briantais & Baker (1989, Biochimica et Biophysica Acta 990, 87-92), was simultaneously measured with a modulated fluorometer. A model was written for rates of CO2 fixation as a function of the true rate of O-2 evolution measured by fluorescence analysis (J(O2)), mesophyll conductance and intercellular CO2 partial pressure. a second model mas developed for rates of CO2 fixation as a function of J(O2), mesophyll conductance and stomatal conductance. In the latter case, leaf stomatal conductance was simulated using the stomatal model proposed by Leuning (1995, Plant, Cell and Environment 18, 339-355). The rates of CO2 fixation predicted from the models were similar to rates measured by IRGA. The results indicate that there is potential to measure CO2 fixation in C-3 plants by combining the non-invasive measurement of J(O2) by chlorophyll fluorescence analysis with the stomatal conductance model.