Physiological and Isotopic Aspects of Photosynthesis in Peperomia

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Abstract
Physiological and isotopic aspects of several Peperomia species were investigated. All but one species had C3-like stomatal behavior, in that stomata were open during the day and closed during the night. In these species, most atmospheric CO2 uptake occurred during the day. Concurrent with this stomatal behavior, there were Crassulacean acid metabolism-like acid fluctuations in most species. Carbon and hydrogen isotope ratios of cellulose nitrate from Peperomia reflect their physiological behavior. The δ13C values of cellulose nitrate from Peperomia species were similar to values observed in C3 plants and consistent with the daytime uptake of exogeneous CO2 via the C3 photosynthetic pathway. The δD values of cellulose nitrate from Peperomia species approach those of Crassulacean acid metabolism plants. These elevated δD values are caused by fractionations occurring during biochemical reactions and not as a consequence of water relations.