Temperature and Humidity Effects on Dark CO2 Fixation by Kalanchoe pinnata

Abstract

Summary Net CO2 exchange and acid accumulation during 12 h dark periods were measured in attached leaves of K. pinnata in a range of leaf temperatures from 12–25°C and at high and low leaf-air water vapor deficits. The results showed that 1. Stomatal opening during the dark period was highly sensitive to air humidity at all temperatures tested. Reduction in stomatal conductance resulted in lowered total CO2 fixation integrated over the 12 h dark period; 2. Maximal rates of dark CO2 fixation were similar at all temperatures tested within a given range of leaf-air vapor pressure deficit. However, beginning of net dark CO2 fixation and time to reach peak rate of CO2 uptake were delayed as temperature increased. Therefore, net CO2 uptake and acid accumulated were reduced with increasing temperature during the dark period; 3. A linear relationship between net CO2 fixation and acid accumulation was obtained, its slope was parallel to the 2 : 1 acid/CO2 ratio line.