Relationship between Respiration and CAM-Cycling in Peperomia camptotricha

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Abstract
Mature leaves of well-watered Peperomia camptotricha show Crassulacean acid metabolis (CAM). Young leaves show CAM-cycling in which CO2 uptake occurs during the day concomitant with a marked diurnal fluctuation of organic acids as in CAM. Evidence is presented suggesting that respiration is the source of CO2 for nocturnal acid synthesis in leaves exhibiting CAM-cycling. Respiratory quotients for these leaves were consistently much less than unity despite the fact that the leaves metabolize starch. The conservation of CO2 by refixation into acids at night represents about 17% of the total photosynthetically fixed CO2 and about 50% of the total respiratory CO2.