Seasonal variation in photosynthesis and diel carbon balance under natural conditions in two Peperomia species that differ with respect to leaf anatomy1

Abstract

Abstract The occurrence of crassulacean acid metabolism (CAM) and C3 photosynthetic activities in Peperomia species has been linked to the differential distribution of C3 and C4 photosynthetic enzymes within the distinct leaf tissue layers. Our objectives were to test if relative thickness of the spongy mesophyll layer is an indication of CAM and if the distribution of water in the leaf tissue changes in response to drought. Under field conditions we studied photosynthesis and water relations of Peperomia obtusifolia and P. macrostachya, species that differ in leaf anatomy. Gas exchange and titratable acidity were measured over a complete 24 hour photoperiod. Plant water status was determined at dawn while chlorophyll a fluorescence data were collected during the day (12 noon). Thickness of the distinct leaf layers was determined with the aid of a calibrated light microscope. Gas exchange and titratable acidity showed that when well-hydrated, P. obtusifolia has typical C3 activity and P. macrostachya has ...