The Effects of Thermoperiod on the Carbon Dioxide Uptake and Compensation Point of the Pineapple Plant, Ananas comosus (L.) Merr.

Connelly, Paul Raymond
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The effects of several thermoperiods on the co2 compensation points and CO2 uptake rates of the youngest fully expanded leaf of pineapple (Ananas comosus (L.) Merr.) were measured. Three to nine days of adaptation at a specific thermoperiod were required to obtain uniform uptake rates. CO2 compensation points, determined just after the lights were turned on, varied from a high of 170 ppm at a 35 C light-15 C dark thermoperiod to O ppm at a constant temperature of 25 C. Values for the other thermoperiods generally decreased as the difference between the light and dark temperature was decreased. The results indicate involvement of different enzyme systems in CO2 fixation at the different thermoperiods. The CO2 equilibrium, with no CO2 supplied, was monitored continuously for periods up to 4 days. At 20 C in the dark essentially all the CO2 was extracted from the sealed chamber. Extraction efficiency of the leaf in the dark decreased with increasing temperature. In the light at a 35 C light-30 C dark thermoperiod, the CO2 concentration ranged from 69 to 200 ppm. Lower maxima were measured at a dark temperature of 20 C and at a 25 C light-20 C dark thermoperiod. No diurnal cycling in the CO2 concentration was observed in continuous light or dark at constant temperatures of 20 or 25 C. When the co2 concentration was maintained at 300 ppm, co2 uptake was maximal at the constant thermoperiods and ranged from 53 to 109 mg dm-2 for 24 hours as temperature was increased from 15 to 30 C. Fixation decreased to 50 percent of the maximum at a constant temperature of 35 C. At a constant dark temperature, the mg of co2 fixed in the light and total mg for 24 hours decreased as the temperature of the light period was increased from 15 to 40 C. When the difference between the light and dark temperatures was 5 C or greater, 15 to 20 mg co2 dm-2 were fixed in the dark even at temperatures of 30 C. The percent of CO2 fixed in the dark ranged from Oat a constant temperature of 25 C to 86 at a 40 C light-25 C dark thermoperiod. Total co2 fixation decreased as the percent of CO2 fixed in the dark increased. The dominant factor determining CO2 fixation rates of pineapple under these conditions appeared to be the amount of CO2 fixed in the dark. Dark fixation was determined primarily by the difference between the light and dark temperature and, to a lesser degree, by the actual temperature.
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