| Elevated atmospheric CO2 concentration ([CO2]) has profound effects on plant growth and development by increasing photosynthesis and enhancing yield in terms of seed production. To study the reproductive response of trees and agricultural crops in terms of seed production under elevated atmospheric [CO2], two approaches were used. First, Pinus taeda L. seeds that developed under ambient or elevated (ambient + 200 mu1-1) CO2 were collected from Duke Forest, North Carolina, USA in October 1998. Seeds were germinated in nutrient-deficient soil in either ambient or elevated greenhouse chambers and allowed to grow for 120 d. Seeds that developed in elevated [CO2] had 91% and 265% greater weight and lipid content, respectively, and three times the germination success compared to those developed in current ambient [CO2]. The elevated CO2 seed source generally produced taller seedlings when grown under elevated [CO2]. Seedlings from the elevated seed source also had greater root length, greater specific root length, more needles, and higher nitrogen concentration regardless of greenhouse chambers. Due to deficient soil nutrients, seedlings grown in greenhouse chambers with elevated [CO2] exhibited down-regulation of photosynthesis, regardless of seed source, compared to the ambient seed sources.;Second, the reproductive responses of agricultural crops to CO2 enrichment were reviewed from the primary literature. My objective was to determine if the particular CO2 response of a species can be predicted from its usual reproductive biology. Three agricultural and one weed crop were reviewed as case studies. It was found that doubling of [CO 2] generally enhances the basic reproductive response of these plants either by producing greater numbers of seeds or increasing the seed size. At ambient [CO2], total seed yield is limited by carbohydrate limitations. Under CO2 enrichment, however, plants tend to increase their seed yield simply by enhancing photosynthesis and/or reproductive organs. The seed yield of a plants may, therefore, be regulated by one of the following three reproductive modes: (1) plants with clusters of flowers and exclusive indeterminate growth habit, tend to produce more seeds, (2) plants with clusters of flowers and with exclusive determinate growth habit tend to produces larger seeds, and (3) plants with single flowers, tend to produce both more and larger seeds with the possibility of more seeds if abortion is not a limiting factor. |
