Effect of Oxygen and carbon Diozide Concentrations on Gross Dark CO₂ Fixation and Dark Respiration in Bryophyllim diagremontiaum

Abstract

Effects of O2 and CO2 concentrations on the rates of net and gross dark CO2 fixation in B. daigremontianum were examined. Raising [CO2]i from 60 to 420 µll-¹ resulted in a decrease in the rate of dark respiration, increase in the rate of gross dark fixation (GDF) and shortened the time taken to reach maximum rate of GDF. However, cumulative GDF was relatively unaffected by [CO2]i at that range. At 14°C, lowering [O2] from 21 to 1.5 % had little effect on the rates and time course of dark respiration and GDF. However, at 24°C, this caused a drop in the rate of dark respiration, changed the time dependence of GDF and slightly increased cumulative GDF. Consequently, at 24°C cumulative net CO2 uptake was 3 .3 times higher at 1 .5 % versus 21% O2. These data are discussed in view of the suggested hypothesis that the amount of available substrate, at the end of the light period, is a principal component of the regulation of the amount of gross dark fixation and dark respiration in the following dark period.