Photosynthetic efficiency of young Rhizophora mangle L. in a mangrove in southeastern Brazil.

The study proposes to evaluate the photosynthetic plasticity of Rhizophora mangle L. in four mangrove sites distributed along with the Great Vitória Estuarine System. The variation in organic matter content, which implies the higher essential nutrient availability, contributed to better energy flux performance related to electron transport. Furthermore, salinity damaged the reaction centers (RC), since the site with the highest salinity showed changes in the number and size of active photosynthetic RC and in the specific energy flows per active RC (absorption flux, trapped energy flux, and dissipated energy flux), but the plasticity of the species in response to salt stress was confirmed by the increase of performance index for energy conservation (PI_Total), net photosynthetic rate (P _N), and the water-use efficiency (WUE). Also, the results showed that the luminous intensity available compromises the functionality of PSII, in turn, it increases WUE. The results indicate the effect of the chlorophyll a content, which provides more substrate for light absorption, on the electron flow and PI_Total is related to P _N and WUE. The study indicates the ecological plasticity of R. mangle to the conditions of the evaluated area.