The energetic cost for a plant to produce reproductive structures is termed reproductive effort and is most frequently expressed as the ratio of reproductive biomass to total plant biomass. This expression may lead to an incorrect analysis of reproductive effort unless an account is taken of (a) the cost of producing male flowers or male flower parts, and (b) the photosynthetic contribution (reproductive assimilation) of reproductive structures to propagule production.
An analysis was made of the carbon budget for reproduction in Ambrosia trifida L., based on measurements of CO2 flux, and the elaboration of seed by excised immature pollinated inflorescences in the absence of carbohydrate from the main stem. Reproductive assimilation accounted for 41 and 57 % respectively of the carbohydrate required to produce male and female inflorescences on intact plants. Individual flowers retain their ability to elaborate seed even after being removed from the parent plant at the time of pollination.