COMPARATIVE WATER-USE EFFICIENCIES OF 3 SPECIES OF PEPEROMIA (PIPERACEAE) HAVING DIFFERENT PHOTOSYNTHETIC PATHWAYS

Water-use efficiencies (WUE) were compared among three species of Pepe romia (Piperaceae) selected for their diversity in photosynthetic path ways. Peperomia obtusifolia is a C-3 plant that exhibits a small degre e of CAM-cycling; P. camptotricha is a C-3-CAM intermediate, having re latively high rates of CO2 uptake during both the day and the night; a nd P. scandens is a CAM plant. All three congeners have succulent leav es and share a similar ecological niche; they typically grow as epiphy tes (occasionally as terrestrials) in tropical and subtropical forests . Thus, these species of Peperomia provide an ideal set of truly compa rable plants to test the long-held, but recently challenged, generaliz ation that the WUE of CAM plants is substantially greater than that of non-CAM species. Although daytime values of WUE were lower in P. scan dens than in P. obtusifolia and P. camptotricha, values of nighttime W UE and 24-hour WUE for the CAM species greatly exceeded corresponding values for the other two Peperomia species. Thus, the results of this study support past generalizations that a high WUE is a consequence of the CAM photosynthetic pathway.