Pathways of CO₂ Fixation in the Cam Plant Kalanchoe daigremontiana. III. Correlation With δ¹³C Value During Growth and Water Stress

Abstract

Seedlings of K. daigremontiana were grown in the same controlled-environment room under nine different day temperature and light regimes. In each treatment, irrigated plants maintained dawn water potentials of approximately -5 bar whereas droughted plants ranged to -22 bar. Irrigated plants showed a characteristic stomatal opening on illumination, closure during deacidification and partial stomatal opening following deacidification. Stomata of droughted plants remained closed throughout the light period. Irrigated and droughted plants showed comparable dark acid synthesis. Low light levels and low day temperature resulted in lower dark acid synthesis and more protracted deacidification in the light. The δ¹³C value (total carbon) of old as well as newly formed leaves of irrigated plants tended to become less negative throughout the experiment except in low-light, low-day-temperature treatments. This trend was accentuated in the δ¹³C value (total carbon) of whole shoots of droughted plants. These data are consistent with an increase, with age, in the proportion of CO₂ assimilated in the dark during growth of irrigated plants, and with the greater dependence on dark CO₂ assimilation during the slower growth of droughted plants. Differences in the δ¹³C value of soluble and insoluble carbon from irrigated and droughted plants assayed at dawn appear to be consistent with the established starch to acid relationships in crassulacean plants.