Nearly all of earth's plant life responds favorably to increases in the air's CO2 content by exhibiting enhanced rates of photosynthesis and biomass production. However, most research in this area has been conducted on agricultural, forage and tree species. Thus, it is important to determine how horticultural species - especially flowers - respond to atmospheric CO2 enrichment, as well as how floral characteristics of other types of plants respond.
In a complex experiment conducted by Niu et al. (2000), yellow and primrose pansies (Viola x wittrockiana) increased their total dry weights by 10 to 30% in response to a 600-ppm increase in the CO2 content of the air. In addition, atmospheric CO2 enrichment increased flower size by 4 to 10%. Similarly, Lake and Hughes (1999) found that a 380-ppm increase in the air's CO2 concentration elicited a 35% increase in the total plant biomass of nasturtiums (Tropaeolum majus). Atmospheric CO2 enrichment did not affect flower size in this species, however; but total flower nectar volume produced by the CO2-enriched nasturtiums was 2.4-fold greater than that produced by ambiently-grown control plants. Likewise, Dag and Eisikowitch (2000) reported that atmospheric CO2 enrichment up to 1,000 ppm doubled both the average nectar volume and sugar production per flower in greenhouse-grown melons (Cucumis melo).
In the study of Johnson and Lincoln (2000), an annual plant native to the southeastern USA (Heterotheca subaxillaris) increased its total biomass by 20% in response to a 300-ppm increase in the air's CO2 content. Moreover, elevated CO2 increased reproductive flower biomass and induced flowering much earlier in CO2-enriched plants than it did in ambiently-grown plants. In the interesting study of Aloni et al. (2001), a 450-ppm increase in the air's CO2 content completely ameliorated a 75% high temperature-induced reduction in bell pepper (Capsicum annuum L.) pollen production that was observed under ambient CO2 concentrations. In addition, although high temperature reduced the number of seeds produced per fruit in ambiently-grown plants by 68%, it only reduced this parameter by 9% in CO2-enriched plants. Lastly, twice-ambient concentrations of atmospheric CO2 have also been reported to increase pollen production in ragweed by 61% at the stand-level (Wayne et al., 2002).
These several observations suggest that flowers in a CO2-enriched world will likely produce greater amounts of pollen and nectar, which should favor their pollination, seed production and survival.
References
Aloni, B., Peet, M., Pharr, M. and Karni, L. 2001. The effect of high temperature and high atmospheric CO2 on carbohydrate changes in bell pepper (Capsicum annuum) pollen in relation to its germination. Physiologia Plantarum 112: 505-512.
Dag, A. and Eisikowitch, D. 2000. The effect of carbon dioxide enrichment on nectar production in melons under greenhouse conditions. Journal of Apicultural Research 39: 88-89.
Johnson, S.L. and Lincoln, D.E. 2000. Allocation responses to CO2 enrichment and defoliation by a native annual plant Heterotheca subaxillaris. Global Change Biology 6: 767-778.
Lake, J.C. and Hughes, L. 1999. Nectar production and floral characteristics of Tropaeolum majus L. grown in ambient and elevated carbon dioxide. Annals of Botany 84: 535-541.
Niu, G., Heins, R.D., Cameron, A.C. and Carlson, W.H. 2000. Day and night temperatures, daily light integral, and CO2 enrichment affect growth and flower development of pansy (Viola x wittrockiana). Journal of the American Society of Horticultural Science 125: 436-441.
Wayne, P., Foster, S., Connolly, J., Bazzaz, F. and Epstein, P. 2002. Production of allergenic pollen by ragweed (Ambrosia artemisiifolia L.) is increased in CO2-enriched atmospheres. Annals of Allergy, Asthma, and Immunology 88: 279-282.