Temperature Dependence of Dark CO₂ Fixation and Acid Accumulation in Kalanchoe daigremontiana

Abstract

Kalanchoe daigremontiana was grown at 25/15 and 34/24°C and net CO₂ fixation and acid synthesis were measured at 8, 15 and 24°. The ratio of net dark CO₂ fixation to acid accumulation was nearly 1 at all temperatures tested. Although the increased contribution of respiratory CO₂ to total acid synthesis at high temperatures was demonstrated by incubating leaf discs in CO₂-free air, it was not enough to account for the reduction of dark CO₂ fixation. Plants grown at 25/15° temperature regime showed maximal rates of nocturnal acid accumulation at 15°, the rates decreasing markedly at 24°. Plants grown at 24/34° showed similar rates at 15 and 24°, but acid accumulation was significantly lower at 8°. Measurements of dark acid accumulation in CO₂-free air indicated that 34/24° plants have reduced respiration rates in comparison with 25/15° plants. These observations are discussed in relation to hypotheses seeking to account for effects of temperature on crassulacean acid metabolism.