C3 photosynthesis and high temperature acclimation of CAM in opuntia basilaris engelm. and bigel.

Carbon fixation by CAM at high night temperatures was examined in the stem succulent, Opuntia basilaris. Nighttime accumulation of titratable acids was uniformly high among plants growing naturally along an altitudinal temperature gradient in Death Valley, California during the hot summer period. Plants grown at high temperature regimes (40°/30°C) had rates of CAM and C3 fixation similar to rates observed in plants maintained at a cool temperature (20°/10°C). C3 fixation comprised 30% of the total carbon fixed by the potted, well watered plants. However, when pads were excised, C3 fixation was suppressed while CAM continued unabated.