It is widely predicted that atmospheric CO2 concentrations will double from 350 ppm to 700 ppm within the next one hundred years. The impact of elevated CO2 on biological systems is of considerable interest. As the amount of fixed carbon available to a plant increases, both growth and reproduction may increase. If increases in reproduction, and hence fitness occur and they increase differentially among species populations or genotypes, the increases in [CO2] may affect community structure, and/or selection within populations. While changes in reproductive output as a result of increased levels of CO2 have been shown in various species, generally these studies have focused on developing seeds and ovaries - the female half of plant reproduction; considerably less information exists about these effects on developing pollen grains - the male half of plant reproduction. Wild radish, Raphanus sativus, was used as a model organism to study the effects of elevated ambient CO2 on male reproductive success. Sibling pairs of pollen donors were grown in growth chambers in one of two CO2 levels, ambient (~ 360ppm) or elevated (~700ppm). Pollen collected from these plants was used to pollinate a set of unrelated plants. In addition to the pollinations, flowers and pollen were collected from the donors in order to measure pollen quality and quantity. Results will be discussed in terms of siring success, offspring seed weight, amount of pollen produced, and pollen germination ability.

Key words: Brassicaceae, CO2, pollen competition, pollen production, Raphanus sativus, seed paternity