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Abstract

We tested if two Amazonian floodplain tree species, , Laetia corymbulosa (Flacourtiaceae) and Pouteria glomerata (Sapotaceae), react in a similar way to the extreme changes of hydrologic conditions. They have several features in common and both belong to the "alternative energy metabolism" strategy. A strong leaf loss and significant reduction of new leaf production was observed in L. corymbulosa in a period of unusually strong drought, accompanied by a significant decrease in predawn leaf water potential. P. glomerata was not affected by drought, but showed a complete inhibition of new leaf production in the period of highest water levels. Photosynthetic activity in L. corymbulosa was highest in the terrestrial phase (13 µmol CO2 m-2 s-1). In the first week after inundation net CO2-exchange rates were comparable to those of the terrestrial phase, but dropped drastically to 3 µmol CO2 m-2 s-1 after approx. six months of waterlogging. In contrast, assimilation rates of P. glomerata were nearly constant during the whole annual cycle, ranging between 8 and 12 µmol CO2 m-2 s-1. The results show that L. corymbulosa reacts more sensitively to both drought and long-term waterlogging than P. glomerata. Both species which belong to the same strategy group as defined by root metabolism show predictable reactions to the changing hydrological conditions, and the reactions are linked to the hydric environment. On the other hand, they show very different phenological and physiological patterns and thus stand for the high diversity of species and of strategies of trees of Várzea floodplains.