Comparing Hydraulic Strategies Across Three Species of Clusia Differing in Expression of CAM Photosynthesis

Crassulacean acid metabolism (CAM), the night time fixation of CO2 and daytime stomatal closure, may be linked to differences in hydraulic traits in the plants in which it is expressed. Three species of Panamanian Clusia, expressing differing levels of CAM strength (measured as a factor of their carbon isotope discrimination) were measured on variables of water relations. Leaves of the strong CAM species Clusia rosea showed a high modulus of elasticity (ε), high relative water content at turgor loss point (RWCTLP), and a low absolute capacitance at full turgor (CFT*), suggesting a strategy that retains water better than the intermediate CAM species Clusia uvitana, with a low ε, RWCTLP, and a high CFT*. With C. rosea expressing a high level of growth habit variability, and increased strength of CAM over C. uvitana in the same region, may represent a development of different strategies allowing these two plants to persist in the same habitat – with CAM strength potentially contributing to an increase in ability to adapt to multiple growth habits. The C3/facultative CAM Clusia pratensis, also persisting in the same geographic range, showed values intermediate of C. rosea and C. uvitana, and its persistence primarily as a tree, with limited CAM expression, may also be an adaptation to coexist in the same range as C. rosea and C. uvitana