PERSPECTIVES IN COMPARATIVE ECOPHYSIOLOGY OF SOME BRAZILIAN VEGETATION TYPES: LEAF CO2 AND H2O GAS EXCHANGE, CHLOROPHYLL A FLUORESCENCE AND CARBON ISOTOPE DISCRIMINATION

Abstract

Photosynthetic activity is responsible for the energy plants use for growth, defense and reproduction. Therefore, photosynthesis is fundamental to plant metabolism However, the effects of environmental factors on net CO₂ assimilation rates are as yet poorly known in Brazilian vegetation types. A decrease in net CO₂ uptake may be related to a decrease in CO, diffusion to the carboxylation sites due to partial or total stomata closure and to direct inhibition 01' primary and secondary photosynthetic processes in the chloroplasts. Photosynthetic carbon reduction is one of the rnost important pathways for the utilization of light energy. Hence, lower rates of CO, uptake may cause an excess of excitation energy through the photosystems and consequently le ad to a decline in the efficiency of photosynthetic energy conversion. The study of comparative ecophysiology of native species is essential for understanding the mechanisms that lead to the high diversity of the Brazilian flora. CO, and H₂O gas exchange, chlorophyll a fluorescence and carbon isotope discrimination are powerful and predictive tools for addressing the influence of multi pie environmental factors on plant performance in situ. Here 1 discuss the results of comparative plant physiological ecology studies in several Brazilian vegetation types.