Under natural condition and without water deficit, assimilation of CO2 (A) and transpiration (E) rates, stomatal conductance (g) and photosyntetic efficiency of water use (E/A), were monitored daily on maize (C4), rice (C3) and wheat (C3). In all species, the shape of response curves of A in function of irradiance (I), was a retangular hyperbole. However, luminic saturation was not observed in maize. Stomatal conductance response curve in function of I was also a retangular hyperbole, while E was linear in all species. Due to differential response of A and E, as a function of I as well as g, the ratio E/A was increased with the increase of I. The C3 species (rice and wheat) showed higher values of E/A than the C4 specie (maize), in all levels of I and g, showing the better C4 adaptation when stomatal limitation aperture occurs.
rice; Oryza sativa L.; maize; Zea mays L.; wheat; Triticum aestivum L.; photosynthesis; transpiration