Responses of some North American CAM plants to freezing temperatures and doubled CO2concentrations: implications of global climate change for extending cultivation

Environmental influences on the cultivation of Crassulacean acid metabolism (CAM) plants, which are especially well adapted to arid regions with limited rainfall, were evaluated with respect to two aspects of global climate change. Cellular uptake of a vital stain, which occurs in living cells only, was halved at −6 ± 1°C for the cultivated CAM speciesAgave salmiana,Opuntia ficus-indicaandStenocereus queretaroensisgrowing at day/night air temperatures of 30°C/20°C compared with −12°C for the wild speciesOpuntia humifusa. When plants were grown at reduced temperatures of 10°C/0°C, stain uptake was halved at about −8°C for the cultivated species but at −24°C forO. humifusa. The greater low-temperature sensitivity and the lesser low-temperature acclimation of the cultivated species severely limit the regions where they can presently be grown, but such regions will expand as air temperatures rise accompanying global climate change. When the atmospheric CO2concentration was doubled from the current ambient value of 360 μmol mol−1to 720 μmol mol−1, net CO2uptake over 24-h periods increased 36% forA. salmianaandS. queretaroensis; about one-third of the increase resulted from higher net CO2uptake rates in the last 4 h of daytime and two-thirds from higher rates during the first 8 h of the night. The doubled atmospheric CO2concentration predicted to occur before the end of the twenty-first century will increase CO2uptake and hence biomass productivity of such CAM species, further expanding the regions where they may be profitably cultivated.