EFFECT OF ELEVATED CO2 ON GROWTH AND CRASSULACEAN-ACID-METABOLISM ACTIVITY OF KALANCHOE-PINNATA UNDER TROPICAL CONDITIONS

Kalanchoe pinnata (Lam.) Pers. (Crassulaceae), a succulent-leaved cras sulacean-acid-metabolism plant, was grown in open-top chambers at ambi ent and elevated (two times ambient) CO2 concentrations under natural conditions at the Smithsonian Tropical Research Institute, Republic of Panama. Nocturnal increase in titratable acidity and nocturnal carbon gain were linearly related, increased with leaf age, and were unaffec ted by CO2 treatments. However, under elevated CO2, dry matter accumul ation increased by 42-51%. Thus, the increased growth at elevated CO2 was attributable entirely to increased net CO2 uptake during daytime i n the light. Malic acid was the major organic acid accumulated overnig ht. Nocturnal malate accumulation exceeded nocturnal citrate accumulat ion by six- to eightfold at both CO2 concentrations. Basal (predawn) s tarch levels were higher in leaves of plants grown at elevated CO2 but diurnal fluctuations of starch were of similar magnitude under both a mbient and elevated CO2. In both treatments, nocturnal starch degradat ion accounted for between 78 and 89% of the nocturnal accumulation of malate and citrate. Glucose, fructose, and sucrose were not found to e xhibit marked day-night fluctuations.