Effects of elevated CO2 on time of flowering in four short-day and four long-day species

Abstract

This study was undertaken to determine if the effect of elevated CO2 on flowering phenology is a function of the photoperiodic response of the species involved. Four long-day plants, Achillea millefolium, Callistephus chinensis, Campanula isophylla, and Trachelium caeruleum, and four short-day plants, Dendranthema grandiflora, Kalanchoe blossfeldiana, Pharbitis nil, and Xanthium pensylvanicum, were grown under inductive photoperiods (9 h for short day and 17 h for long day) at either 350 or 1000 μL/L CO2. Time of visible flower bud formation, flower opening, and final plant biomass were assessed. Elevated CO2 advanced flower opening in all four long-day species and delayed flowering in all four short-day species. In the long-day species, the effect of CO2 was primarily on bud initiation; all four species formed buds earlier at high CO2. Bud development, the difference in time between flower opening and bud initiation, was advanced in only one long-day species, Callistephus chinensis. Mixed results were obtained for the short-day species. Elevated CO2 exerted no effects on bud initiation but delayed bud development in Dendranthema and Kalanchoe. In Xanthium, bud initiation rather than bud development was delayed. Data on bud initiation and development were not obtained for Pharbitis. The negative effect of CO2 upon phenology in the short-day species was not associated with negative effects on growth. Elevated CO2 increased plant size in both long-day and short-day species. Key words: phenology, bud initiation, flower opening, size at flowering, photoperiodism.