C3 Photosynthesis and Crassulacean Acid Metabolism in a Kansas Rock Outcrop Succulent, Talinum calycinum Engelm. (Portulacaceae)

The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent Talinum calycinum in central Kansas. Field studies revealed CAM-like diurnal acid fluctuations in these plants. These fluctuations persisted under all moisture and temperature regimes in the laboratory. Despite this CAM-like acid metabolism, simultaneous gravimetric determinations of day- and nighttime transpiration rates indicated the presence of a C(3) gas exchange pattern. Subsequent analyses of diurnal CO(2) and H(2)O exchange patterns under well-watered conditions and after 3, 5, and 7 days of drought confirmed these findings, though low rates of nocturnal CO(2) uptake were observed on the fifth night after continuous drought. Finally, the delta(13)C/(12)C value of this succulent, -27.8 per thousand, emphasizes the insignificance of any nocturnal CO(2) uptake in the lifelong accumulation of carbon in this species. Thus, it is proposed that T. calycinum is a C(3) plant with some CAM characteristics, including the ability to re-fix respiratory CO(2) at night under all moisture regimes, potentially resulting in a conservation of carbon, and occasionally to fix atmospheric CO(2) at night. These findings may prove to be common among rock outcrop succulents.