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

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Abstract
The differences in the costs of reproduction between males and females of dioecious plants should lead to differences in life history evolution, but photosynthesis of reproductive structures can reduce the cost of these structures. We hypothesised that the greater costs of reproduction would select for greater photosynthetic capacity in reproductive structures of female plants of the dioecious species Aciphylla glaucescens. However, measurements of gas exchange using a portable infra‐red gas analysis sytem showed that the photosynthetic capacity of male inflorescences is greater, and their total mass is half that of females. Thus, male inflorescences contribute more to their own carbon and energy costs. Estimates of the contribution of inflorescence photosynthesis suggest that much of the reproductive biomass is attributable to import of photo‐synthate from the leaves. Total nitrogen investment in reproductive structures was much greater in females. Life history differences between males and females may be driven by nitrogen or ecological factors rather than by carbon acquisition or energy requirements.