Effects of elevated CO2 on growth and morphological characteristics of ornamental bromeliads

Three ornamental bromeliads, i.e. Aechmea ‘Maya’ (CAM), Aechmea fasciata ‘Primera’ (CAM) and Guzmania ‘Hilda’ (C3) were grown under greenhouse conditions at ambient (380 ppm) and elevated (750 ppm) CO2. The effects of long-term exposure (34 weeks) to elevated CO2 on growth and morphological traits constituting the ornamental value were assessed.Aechmea ‘Maya’ and A. fasciata ‘Primera’ showed a different growth response to elevated CO2 exposure. Aechmea ‘Maya’ showed for both CO2 concentrations an equal biomass enhancement throughout the experimental period. In accordance leaf micromorphology remained unaffected. For A. fasciata ‘Primera’ CO2 fertilisation led to a decreased biomass production (25% less fresh and dry weight) due to a reduced total leaf area (41%) and lower leaf thickness (9%). These responses of both Aechmea hybrids are quite uncommon for CAM plants.Doubling the atmospheric CO2 concentration stimulated growth for Guzmania ‘Hilda’ shown by an increase in total leaf area (34%) and leaf thickness (11%). However, the surplus in biomass production (57% more fresh weight and 69% more dry weight) was gained only in the first 22 weeks of the experiment as afterwards acclimation occurred.For all three bromeliads elevated CO2 exposure led to adverse effects on the ornamental value. Leaves from high CO2 grown plants displayed a visual paler green colour than leaves from control plants due to halving of the total chlorophyll content. Furthermore, allometric relations changed between leaf length and leaf width causing a more compact plant shape. This ultimately resulted in the loss of the typical plant shape for ornamental bromeliads with long and slender leaves.Overall the results in the current study show that long-term exposure to elevated CO2 does not always lead to enhanced biomass production. Moreover it can lead to adverse effects on the ornamental value. Thus, it is apparent that caution is needed with the application of CO2 fertilisation in commercial ornamental cultures. The CO2 plant response can seriously differ among individual species in one family and even in one genus. Therefore it is important to realise that the study of only one representative for a certain plant family or a genus is not adequate to make the proper interpretations concerning general CO2 responses!