plant biomass accumulation over several months of treatment [120] or leaf CO 2 assimilation rates mon-
itored over the entire 24-hr diel period when plants were well irrigated [121]. In contrast, phase IV CO 2
assimilation that commences in the late daylight period and overall plant growth rates were consistently
higher in the CO 2 -enriched, water-limited plants [120,121]. Plants of Kalanchoealso did not show en-
hanced rates of CO 2 uptake under supranormal growth [CO 2 ] [122,123]. For Agave desertiandFero-
cactus acanthodes, when growth [CO 2 ] was raised 300 ppm above ambient, short-term net CO 2 uptake
over 24 hr and long-term dry biomass gain over 1 year were enhanced about 30% for both plants [124].
InOpuntia ficus-indica, long-term CO 2 enrichment increased net CO 2 uptake, water use efficiency, root
growth, stem thickness, and biomass production but decreased activities of PEPC and Rubisco [30,125].
Doubling the ambient [CO 2 ] also increased levels of glucose, starch, and nocturnal malate production
and enhanced activities of sucrose synthase and soluble starch synthase for this perennial CAM species
[126].RESPONSES TO RISING CO 2 AND CLIMATE CHANGE 41Figure 2 Leaf area (A), aboveground dry weight (B), juice volume (C), and leaf photosynthesis (D) of
sugarcane (cv. CP 73-1547) grown in sunlit temperature-gradient greenhouses under [CO 2 ] of 360 and 700 ppm
and temperatures at 2 and 6.5°C above outdoor ambient temperature (Ta). The four treatments were T1 360
ppm CO 2 / Ta 2°C; T2 360 ppm CO 2 / Ta 6.5°C; T3 700 ppm CO 2 / Ta 2°C; T4 700 ppm CO 2 /Ta
6.5°C.