Despite the potential impact of rising global CO2 levels, only a limited number of studies have been conducted on the effects of ambient and elevated CO2 on plants having Crassulacean acid metabolism (CAM). To our knowledge, there are no studies for pineapple [Ananas comosus (L.) Merr.], the most commercially important CAM plant. Pineapple plants were grown at CO2 levels of ≈330 (ambient) and ≈730 (elevated) μmol·mol-1 in open-top chambers for 4 months. The mean air temperature in the chambers was ≈39 °C day/24 °C night. Average plant dry mass at harvest was 180 g per plant at elevated CO2 and 146 g per plant at ambient CO2. More biomass was partitioned to stem and root but less to leaf for plants grown at elevated CO2; leaf thickness was 11% greater at elevated than at ambient CO2. The diurnal difference in leaf titratable acidity (H+) at elevated CO2 reached 347 mmol·m-2, which was up to 42% greater than levels in plants grown in ambient CO2. Carbon isotopic discrimination (Δ) of plants was 3.75% at ambient CO2 and 3.17% at elevated CO2, indicating that CO2 uptake via the CAM pathway was enhanced more by elevated CO2 than uptake via the C3 pathway. The nonphotochemical quenching coefficient (qN) of leaves was ≈45% lower in the early morning for plants grown at elevated than at ambient CO2, while afternoon values were comparable. The qN data suggested that the fixation of external CO2 was enhanced by elevated CO2 in the morning but not in the afternoon when leaf temperature was ≥40 °C. We found no effect of CO2 levels on leaf N or chlorophyll content. Pineapple dry matter gain was enhanced by elevated CO2, mainly due to increased CO2 dark fixation in environments with day temperatures high enough to suppress C3 photosynthesis.
Characterization of Early Morning Crassulacean Acid Metabolism in Opuntia erinacea var Columbiana (Griffiths) L. Benson
