Brazil plans to construct many new hydroelectric dams in the Amazon region. The new conditions of flooding promoted by reservoirs can alter photosynthetic processes, and the study of physiological responses of trees can be used for selected suitable species to reforest these altered areas. The present study analyzed changes in pigment content and photosynthetic performance in floodtolerant and flood-intolerant species that are common in the floodplains along the Uatuma˜ River and on islands in the reservoir of the Balbina Hydroelectric Dam. Their photosynthetic responses were tested using chloroplast pigment content and chlorophyll a fluorescence. Flooding caused a significant reduction in pigment content in all of the three flood-intolerant species and in one of the seven flood-tolerant species studied. Flood-tolerant species were unaffected and neither a change in their chlorophyll contents nor a decrease in the efficiency of energy use in the photosynthetic process was observed. From chlorophyll a fluorescence transients (OJIP transients) was calculated the performance index (PIABS), a parameter derived from the OJIP transient by means of the JIP-test (translation of original fluorescence measurements into biophysical expressions quantifying the stepwise flow of energy through photosystem II). This parameter was a very sensitive indicator of the physiological status of trees under field and was shown to be a particularly sensitive indicator of stress tolerance in flood-intolerant species during inundation, whereas flood-tolerant species had only minor reductions in their photosynthetic performance. We suggest that tree species selection for reforestation around reservoirs can benefit from species-specific measurements of photosynthetic response using the JIP-tes.
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