Sexual dimorphism and seasonal changes of leaf gas exchange in the dioecious tree Ilex paraguariensis grown in two contrasted cultivation types

Yerba mate (Ilex paraguariensis, Aquifoliaceae) is a Subtropical, evergreen, dioecious, South American tree. In one preliminary study, it was observed that file functional strategy of yeirba mate females, aiming to finish reproductive process, was increased transpiration relative to photosynthetic rates compared with males, oil self-shaded leaves. We hypothesised that the long-term gas exchange response of males and females call evolve independently of phenological stage and cultivation type. In this spirit, the primary aim of the study was to analyse the physiological sexual dimorphism of this species, evaluating fluctuations of gas exchanges related to microclimate and phenological stages. A field study was conducted oil adult plants of yerba mate cultivated ill monoculture (MO) and in forest understorey (FUS), and measurements carried Out in situ oil microclimate and leaf gas exchange parameters. The photosynthetic photon flux density that was attained at leaf level in FUS was reduced roughly 10-fold compared with that in MO. Various leaf age Populations were observed during a 2-year period at 2-month intervals and grouped into four categories: young, young-fully-expanded, fully-expanded and old. Young and youngfully-expanded leaves were the most active in photosynthesis. Leaves of female plants showed greater photosynthetic rate than those of male plants, which was expressed oil all leaf age categories in MO, but Only during vegetative stages previous to flowering and fruit ripening. The photosynthesis of young-fully-expanded leaves of females grown in FUS Was Superior to males but only during winter growth pause. The stomatal conductance differed ill relation to cultivation type and leafage but did not show the sexual differentiation. Physiological sexual dimorphism in yerba mate is shown to be plastic, responding to environmental conditions. The cost associated to the reproduction of yerba mate could be most easily met showing physiological differentiation of both sexes. A higher reproductive investment of females might be compensated for by exhibiting greater leaf photosynthesis than males that occurs in vegetative stages that precede flowering and fruit ripening.154229130