The ecophysiological adaptations of water hyacinth (metal hyperaccumulator) under adverse environmental conditions are not yet
clearly elucidated. This work evaluated photosynthetic pigments and chlorophyll a fluorescence in water hyacinth plants sampled
in different regions (upper, middle and lower) of ParaÃba do Sul river (PSR) and Imbé river, Brazil. Additionally Mn, Fe, Zn, Cu, Cr, Pb
and Ni were quantified on the shoots and roots. Roots were the preferential site of metal accumulation. Cromium was not detected
in the shoots. Iron and Mn were the elements detected in higher concentrations in all samples. Zinc and Cu were detected in higher
concentrations in roots of plants from middle and upper PSR, sites of higher anthropogenic activity. The highest concentrations of
almost all metals were verified in plants from middle PSR. Regarding photosynthetic adaptations, plants from middle and upper PSR
showed the highest concentrations of photosynthetic pigments, as well as the highest values of Fv/Fm and Fv/F0. The photosynthetic
performance of plants suggests that they are not under stress conditions, even in regions of higher anthropogenic activity. Positive
correlation was observed among nonphotochemical quenching and carotenoids, suggesting dissipation of energy in the form of heat
as an strategy to keep the stable photochemical photosynthesis functioning, confirmed by values of the Fv/Fm. It is possible that such
adaptative strategy is efficient as a long term response to stress factors, once literature data suggest that this is not a preferential
path for photosynthesis in stress circumstances under short time controlled conditions.
