Ananas comosus L. (Merr.) (pineapple) was grown at three day/night temperatures and 350 (ambient) and 700 (elevated) µmol mol -1 CO 2 to examine the interactive effects of these factors on leaf gas exchange and stable carbon isotope discrimination (∆,‰). All data were collected on the youngest mature leaf for 24 h every 6 weeks. CO 2 uptake (mmol m -2 d -1 ) at ambient and elevated CO 2 , respectively, were 306 and 352 at 30/20°C, 175 and 346 at 30/25°C and 187 and 343 at 35/25°C. CO 2 enrichment enhanced CO 2 uptake substantially in the day in all environments. Uptake at night at elevated CO 2 , relative to that at ambient CO 2 , was unchanged at 30/20°C, but was 80% higher at 30/25°C and 44% higher at 35/25°C suggesting that phosphoenolpyruvate carboxylase was not CO 2 -saturated at ambient CO 2 levels and a 25°C night temperature. Photosynthetic water use efficiency (WUE) was higher at elevated than at ambient CO 2 . Leaf ∆-values were higher at elevated than at ambient CO 2 due to relatively higher assimilation in the light. Leaf ∆ was significantly and linearly related to the fraction of total CO 2 assimilated at night. The data suggest that a simultaneous increase in CO 2 level and temperature associated with global warming would enhance carbon assimilation, increase WUE, and reduce the temperature dependence of CO 2 uptake by A. comosus.
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