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

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Abstract
The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent T. 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 C3 gas exchange pattern. Subsequent analyses of diurnal CO2 and H2O exchange patterns under well-watered conditions and after 3, 5 and 7 days of drought confirmed these findings, though low rates of nocturnal CO2 uptake were observed on the 5th night after continuous drought. Finally, the .delta.13C/12C value of this succulent, -27.8 .permill., emphasizes the insignificance of any nocturnal CO2 uptake in the lifelong accumulation of carbon in this species. Apparently, T. calycinum is a C3 plant with some CAM characteristics, including the ability to re-fix respiratory CO2 at night under all moisture regimes, potentially resulting in a conservation of C and occasionally to fix atmospheric CO2 at night. These findings may prove to be common among rock outcrop succulents.