Expression of modes of photosynthesis (C-3, CAM) in Clusia criuva Camb. ina cerrado gallery forest transect

The large majority of the cc. 150 species of the neotropical shrub and tree genus Clusia have the potential to perform Crassulacean acid metabolism (C AM). They are either obligate CAM plants or C-3/CAM intermediate plants. On ly a very small percentage of the plants studied so far are apparently obli gate C-3 species. Among these was C. criuva, until recent laboratory studie s showed that it may also have a certain CAM capacity under artificial stre ss conditions. Measurements of stomatal conductance (porometry) and chlorop hyll fluorescence variables of C. criuva occurring along a transect from de ep shade inside a gallery forest across the semi-shaded ecotone towards a c errado and into the exposed cerrado itself in central Brazil now show that it can adapt its photosynthetic apparatus to effective performance of C, ph otosynthesis under highly different photosynthetic photon flux densities. I n addition, however, it does have a certain potential for CAM and cannot be considered as a strictly obligate C, plant, Should a basic capacity for pe rforming CAM be a general property of the genus, the quest for CAM traits i n other remaining putatively obligate C3 species of the genus ought to be p ursued.