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Responses of Pineapple to Elevated CO2 and Temperature
Zhu, J., Goldstein, G. and Bartholomew, D.P. 1999. Gas exchange and carbon isotope composition of Ananas comosus in response to elevated CO2 and temperature. Plant, Cell and Environment 22: 999-1007.

What was done
Pineapple, an agriculturally-important CAM plant, was grown in controlled environment chambers for six months at atmospheric CO2 concentrations of 350 and 700 ppm. In addition, plants were subjected to day/night growth temperatures of 30/20 (which is "optimal" for pineapple growth under ambient CO2), 30/25, and 35/25C to determine their response to elevated CO2 when concomitantly exposed to higher air temperatures characteristic of computer-predicted global warming scenarios.

What was learned
When pineapples were grown at ambient CO2, the total amount of carbon assimilated over a 24-hour period declined by 43 and 39% as day/night growth temperatures were raised from 30/20 to 30/25 and 35/25C, respectively. However, when grown at elevated CO2, the total amount of carbon assimilated over a 24-hour period did not decline with rising air temperatures. In fact, total carbon assimilation was 15, 97, and 84% greater for CO2-enriched plants than it was for ambiently-grown plants at air temperature regimes of 30/20, 30/25, and 35/25C, respectively. In addition, plant photosynthetic water-use efficiency was always significantly greater in CO2-enriched plants, regardless of growth temperature.

What it means
As the atmospheric CO2 concentration continues to rise, CAM plants (like pineapple), which rely heavily upon C4 photosynthesis for assimilating carbon, will likely respond by exhibiting increases in photosynthesis, water-use efficiency, and biomass production. This key paper may have been the first to address the interactive responses of a CAM plant to elevated CO2 and temperature; and it clearly demonstrates that CO2 uptake via C4 photosynthesis can be substantially increased by atmospheric CO2 enrichment, particularly under conditions of higher-than-ambient air temperatures. In fact, the assimilation data from CO2-enriched plants was so robust, it led the authors to suggest that the primary carboxylating enzyme utilized by both C4 and CAM plants (phosphoenolpyruvate carboxylase) "was not CO2 saturated at ambient CO2 and a night temperature of 25C." Thus, the results of this paper also support the notion that C4 plant responses to elevated CO2 need to be re-evaluated, as they certainly are much greater than once thought by some researchers in this field.

Reviewed 1 November 1999