THE EFFECTS OF ELEVATED CO₂ ON PLANTS

Abstract

S ummary Four populations of Phlox drummondii and one population each of Datura stramonium and Abutilon theophrasti were grown in six growth chambers at 300, 600 and 900 μ l l −1 CO 2 , all other environmental variables remaining constant. Changes in timing and numbers of flowers produced were species‐ and population‐dependent. In general, P. drummondii and D. stramonium flowered earlier under high CO 2 while A. theophrasti was not affected. Significant population × CO 2 interactions were found for several flower production characters in P. drummondii , indicating differential response to elevated CO 2 levels even within a species. In D. stramonium , increased biomass in high CO 2 caused significantly larger fruits to be formed, but there was no significant increase in seed number. In A. theophrasti , individual seed weight increased with increasing CO 2 , but total seed weight per plant remained constant. These results are discussed in relation to their possible implications to plant community structure, and the effects on higher trophic levels (e.g. pollinators and plant predators). Qualitative as well as quantitative changes in plants in response to high CO 2 must be studied with care to ensure correct predictions of the effects of the global rise in CO 2 .