Gas exchange and photosynthetic water use efficiency in response to light, CO2 concentration and temperature in Vicia faba.

Light and temperature-response curves and their resulting coefficients, obtained within ecophysiological characterization of gas exchanges at the leaf level, may represent useful criteria for breeding and cultivar selection and required tools for simulation models aimed at the prediction of potential plant behaviour in response to environmental conditions. Leaf-scale gas exchanges, by means of an IRGA open-flow system, were measured in response to light intensity (8 levels from 0 up to 2000 micromol m(-2) s(-1)), CO(2) concentrations (ambient-350 micromol mol(-1) and short-term enriched-700 micromol mol(-1)) and air temperature (from 7 up to 35 degrees C) on three Vicia faba L. genotypes, each representing one of the three cultivated groups: major, equina and minor. The net assimilation rate response to light intensity was well described by an exponential rise to max function. The short-term CO(2) enrichment markedly increased the values of light response curve parameters such as maximum photosynthetic rate (+80%), light saturation point (+40%) and quantum yield (+30%), while less homogenous behaviour was reported for dark respiration and light compensation point. For each light intensity level, the major and minor genotypes studied showed assimilation rates at least a 30% higher than equina. The positive effects of short-term CO(2) enrichment on photosynthetic water use efficiency (WUE) indicate a relevant advantage in doubling CO(2) concentration. In the major and minor genotypes studied, similar assimilation rates, but different WUE were observed. The optimum leaf temperature for assimilation process, calculated through a polynomial function, was 26-27 degrees C and no relevant limitations were observed in the range between 21 and 32 degrees C. Analysis at the single leaf level provided both rapid information on the variations in gas exchange in response to environmental factors and selection criteria for the screening of genotypes.