Abstract:Aims Our objective was to determine the effects of elevated CO2 concentration on photosynthetic characteristics, growth rate, flowering percentage and activity of photosynthetic enzyme in Guzmania `Denise’ and Guzmania `Cherry’. Methods We measured Pn, Gs and Tr under various growth conditions using the Li-6400 and used the data to calculate WUE (water use efficiency, WUE=Pn/Tr). We determined chlorophyll and total soluble sugar levels by the method of Zhang & Qu (2003), starch content by the method of Xu et al. (1998) and rubisco and glycolic acid oxidase levels by the method of Ye et al. (1993). Important findings Under two elevated CO2 concentrations, net photosynthetic rate increased by 6.24%-31.91% and 11.92%- 41.48% over plants grown in ambient CO2 concentration during 30 d. Elevated CO2 concentration caused a marked rise in soluble sugar and starch accumulation in leaves, but significantly reduced stomatal conductance and transpiration rate. In addition, Rubisco activity was increased, and glycolate oxidase activity obviously was decreased. Plant height and leaf area increased 6.94%-14.63% and 1.66%-7.06% over plants grown in ambient CO2. There were 9.71%-20.85% and 2.87%-11.62% increases for (900± 40) μmol CO2•mol-1. Dry and fresh weights also increased with elevated CO2 concentration, as was flowering in Guzmania `Cherry’.