Leaf size versus leaf numbertrade-offs in dioecious angiosperms

We explore the possible role of leaf size/number trade-offs for the interpretation of leaf size dimorphism in dioecious plant species. Total above-ground biomass (both male and female) for three herbaceous dioecious species and individual shoots (from both male and female plants) for three woody dioecious species were sampled to record individual leaf dry mass, number of leaves, dry mass of residual above-ground tissue (all remaining non-leaf biomass), number of flowers/inflorescences (for herbaceous species) and number of branches. For two out of three woody species and two out of three herbaceous species examined, male plants produced smaller leaves but with higher leafing intensityui.e. more leaves per unit of supporting (residual) shoot tissue or plant body massucompared with females. Male and female plants, however, did not differ in shoot or plant body mass or branching intensity. We interpret these results as possible evidence for a dimorphic leaf deployment strategy that promotes both male and female function, respectively. In male plants, capacity as a pollen donor may be favored by selection for a broadly spaced floral display, hence favoring relatively high leafing intensity because this provides more numerous axillary meristems that can be deployed for flowering, thus requiring a relatively small leaf as a trade-off. In one herbaceous species, higher leafing intensity in males was associated with greater flower production than in females. In contrast, in female plants, selection favors a relatively large leaf, we propose, because this promotes greater capacity for localized photosynthate production, thus supporting the locally high energetic cost of axillary fruit and seed development, which in turn requires a relatively low leafing intensity as a trade-off.