Gas exchange and carbon isotope composition of Ananas comosus in response to elevated CO2 and temperature

Ananas comosus L. (Merr.) (pineapple) was grown at three day/night temperatures and 350 (ambient) and 700 (elevated) mu mol mol(-1) CO2 to examine the interactive effects of these factors on leaf gas exchange and stable carbon isotope discrimination (Delta,parts per thousand). All data were collected on the youngest mature leaf for 24 h every 6 weeks. CO2 uptake (mmol m(-2) d(-1)) at ambient and elevated CO2, respectively, were 306 and 352 at 30/20 degrees C, 175 and 346 at 30/25 degrees C and 187 and 343 at 35/25 degrees C, CO2 enrichment enhanced CO2 uptake substantially in the day in all environments. Uptake at night at elevated CO2, relative to that at ambient CO2, was unchanged at 30/20 degrees C, but was 80% higher at 30/25 degrees C and 44% higher at 35/25 degrees C suggesting that phosphoenolpyruvate carboxylase was not CO2-saturated at ambient CO2 levels and a 25 degrees C night temperature. Photosynthetic water use efficiency (WUE) was higher at elevated than at ambient CO2. Leaf Delta-values were higher at elevated than at ambient CO2 due to relatively higher assimilation in the light, Leaf Delta was significantly and linearly related to the fraction of total CO2 assimilated at night. The data suggest that a simultaneous increase in CO2 level and temperature associated with global warming would enhance carbon assimilation, increase WUE, and reduce the temperature dependence of CO2 uptake by A. comosus.