Inflorescence photosynthesis and investment in reproduction in the dioecious species Aciphylla glaucescens (Apiaceae)

The differences in the costs of reproduction between males and females of d ioecious plants should lead to differences in life history evolution, but p hotosynthesis of reproductive structures can reduce the cost of these struc tures. We hypothesised that the greater costs of reproduction would select for greater photosynthetic capacity in reproductive structures of female pl ants of the dioecious species Aciphylla glaucescens. However, measurements of gas exchange using a portable infra-red gas analysis sytem showed that t he photosynthetic capacity of male inflorescences is greater, and their tot al mass is half that of females. Thus, male inflorescences contribute more to their own carbon and energy costs. Estimates of the contribution of infl orescence photosynthesis suggest that much of the reproductive biomass is a ttributable to import of photosynthate from the leaves. Total nitrogen inve stment in reproductive structures was much greater in females. Life history differences between males and females may be driven by nitrogen or ecologi cal factors rather than by carbon acquisition or energy requirements.