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

Abstract

The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent Talinum calycinum in central Kansas. Field studies revealed CAM-Iike diurnal acid fluctuations in these plants. These fluctuations persisted under all moisture and temperature regimes in the laboratory. Despite this CAM-Iike acid metabolism, simultaneous gravimetric determinations of day- and nighttime transpiration rates indicated the presence of a d gas exchange pattern. Subsequent analyses of diurnal CO; and H2O exchange patterns under wellwatered conditions and after 3, 5, and 7 days of drought confirmed these findings, though low rates of nocturnal CO, uptake were observed on the fifth night after continuous drought. Finally, the 6 I 3 C / "C value of this succulent, - 27.8%c, emphasizes the insignificance of any nocturnal CO.. uptake in the lifelong accumulation of carbon in this species. Thus, it is proposed that T. calycinum is a ( \ plant with some C AM characteristics, including the ability to re-fix respiratory COj at night under all moisture regimes, potentially resulting in a conservation of carbon, and occasionally to fix atmospheric CO. at night. These findings may prove to be common among rock outcrop succulents.