Carbon Dioxide Exchange Patterns of Cacti from Different Environments

The succulent nature of cacti and their acid metabolism create unusual patterns of CO 2 exchange. Carbon dioxide exchange rates fluctuate at constant temperatures and maintain near normal patterns under abnormal environmental conditions. The typical pattern (i.e., CO 2 release during the day and uptake at night) can be used to determine optimum environmental conditions for maximum net CO 2 uptake and therefore net photosynthesis in cacti. Two species of hedgehog cactic from high elevations are shown to differ in internal nighttime temperature requirements for net CO 2 uptake, an indication of their adaptation to different environments.