Analysis of two indexes water use efficiency in Dactylis glomerata L

The instaneous and the intrinsic water use efficiency were analysed in order to study the mechanisms of water use optimization in Dactylis glomerata L. during the growing season. Net assimilation rate(A), transpiration rate (E) and stomatal conductance (gs) were measured in the leaf of Dactylis glomerata L. and the instantaneous (A/E) and intrinsic water use efficiency(A/gs) were calculated by A, E, gs. In the early stages of biological cycle of Dactylis glomerata L and until May the A/E was higher than A/gs. Early in summer when the water deficit was higher the two indexes seem to be similar. Our results provide indications of water use efficiency optimization during the dry season, decreasing and maintaining more or less the value of gs constant.