Changes in 13C/12C Ratio of CO2 Evolved from CAM Plants with Light Intensities in Relation to Malic Acid Decarboxylation

Carbon dioxide evolved by CAM plants (Aloe vera, Neoregelia sp. Sansevieria guineensis) in light (δ13C = 0.8 ± 1.8%) was significantly enriched in ¹³C relative to that in dark (δ13C = -13.0 ± 1.4%). The changes in S 13C values of CO2 with light intensity revealed curves similar to those of photosynthetic rate versus light. The ratio of the amount of collected CO₂ C_c over the amount of malic acid consumed (C_m) declined sharply from low light to about 95 µmol m⁻² s⁻¹. Thereafter, this decline tended to be slow. The δ¹³C values of CO₂ evolved versus the corresponding C_c/C_m were linearly correlated, showing different slopes for each species, which is consistent with the expectations of the model established in this study. The yields of carbon dioxide for each malic acid decarboxylated evaluated from the model equation, termed N, were 3.0, 1.5, and 1.3 for S. guineensis, A. vera, Neoregelia sp., respectively.