Comparaison du comportement hydrique et de la capacité photosynthétique du maïs et du tournesol en condition de contrainte hydrique. Conclusions sur l'efficience de l'eau

Abstract

Various indices of water stress sensitivity lead to contradictory conclusions as to the choice of irrigated crop between corn and sunflower. We propose an additional analysis of leaf gas exchanges after flowering to field analysis on dry matter and crop water use. Gas exchanges indicated that soil water depletion induces stomatal closure in both plants. For corn, this stomatal closure was accompanied by a reduction in photosynthesis when predawn leaf water potential decreased below -0.2 MPa. Without water stress, stomatal conductance and transpiration were between two and three times higher for sunflower than for corn. The reduction in leaf photosynthesis in sunflower began at a predrawn leaf water potential below -0.5 MPa. For a given value of stomatal conductance, corn leaf photosynthesis was always higher than that of sunflower. Complementary information on physiological mechanisms at leaf level was derived; this should contribute to a better irrigation efficiency at field level.