Comparative Study of the C₃/CAM Intermediate Species Clusia parviflora Saldanha et Engl. and the Obligate CAM Species Clusia hilariana Schlecht. Growing Sympatrically Exposed and Shaded in the Coastal Restinga of Brazil

Abstract

The C₃/CAM intermediate species, Clusia parviflora Saldanha et Engl., and the obligate CAM species Clusia hilariana Schlecht., occur sympatrically in the coastal sand dune vegetation of the Restinga of Brazil. Their photosynthetic activity at an exposed and at a shaded site was compared by measuring gas exchange (porometry), chlorophyll a fluorescence parameters, organic acid levels (malic and citric) and carbon isotope ratios. At the shaded site, low photosynthetic photon flux densities (PPFD) strongly restricted photosynthetic activity. However, C. parviflora could readily make use of light flecks. At the exposed site, C. parviflora was much less affected by photoinhibition than C. hilariana. The CAM species showed higher apparent rates of linear photosynthetic electron transport (ETR) and higher effective quantum yield of PSII (ΔF/F′_m) than did C. parviflora during high insolation in the middle of the day, i.e., the time of Phase III of CAM. Nevertheless, it suffered much more severe acute photoinhibition that was not reversible after 20 min of darkening during this time, and even some chronic photoinhibition not reversible overnight. Comparative studies of sympatric physiotypes with different modes of photosynthesis of a given leaf morphotype, as available in the genus Clusia, challenge some CAM dogmas, e.g., CAM may not always be superior at exposed sites and may not always provide better photoprotection at high PPFD. However, the idea that C₃/CAM plasticity allows occupation of a wider range of habitats is supported.

Key words

Clusia - chlorophyll a fluorescence - crassulacean acid metabolism (CAM) - gas exchange - morphotype - physiotype