Effect of elevated CO2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO2 enrichment (1000 μmol mol−1 vs. control of 380 μmol mol−1). H. undatus plants enriched with CO2 demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO2, in total daily net CO2 uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO2 were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO2, under conditions of CO2 enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO2 uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO2. These results indicate the high potential of CAM plants to respond to CO2 enrichment. It is thus apparent that S. megalanthus grown under CO2 enrichment may benefit from elevated CO2 to a greater extent than H. undatus grown under sub-optimal growth conditions.