Peperomia is a large pantropicalgenus ofmore than 600 species, manyofwhich are epiphytes. A survey indicates that 50% or more ofthe species have Crassulacean acid metabolism (CAM) or CAMcycling. Our assessment of93 taxa is based on the enzymic activities ofP-enolpyruvate carboxylase (PEPc) and pyrophosphate: fructose 6-phosphate phosphotransferase (PFP), diurnal organic acid fluctuation, and nocturnal gas exchange and stomatal opening. During development, the leaves ofthe CAM Peperomia spp. shift from C3-photosynthesis to CAM as evidenced by the appearance of PEPc, the commencement of diurnal organic acid fluctuation, and by a shift from daytime gas exchange to nocturnal gas exchange. There
is some evidence that water-stress will accelerate the induction ofCAM during development. CAM activity may be seasonal in some species, with more activity during the spring and summer than in the winter when growing in glasshouses. Since the photosynthetic mode ofPeperomia may change in response to environmental perturbations such as water-stress, changing photoperiods, seasonally, and during development, the assignment ofa particular mode to a species may be equivocal. Thus, it is possible that all species have some CAM capacity. The presence of CAM metabolism in this epiphytic genus suggests adaptation to drought and water-stress conditions.
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