Physiology of Trees in the Floodplains of the Amazon.

In Central Amazonian floodplains (várzea), trees are subjected to the ‚flood pulse‘, periodic predictable flooding which lasts up to seven months. Linked to the flooding periodicity, the trees show seasonal variations of phenology and physiological activities, as e.g. photosynthetic CO2-assimilation. Under flooding, leaf senescence increases and photosynthetic assimilation declines. Many trees shed their leaves, but before the end of flooding new leaves are flushed and CO2-assimilation rises when the trees are still waterlogged. Phenological and physiological activities are maintained high despite the prolongued period of unfavourable conditions when the roots and stems are flooded, as shown in six species of trees which were measured continuously. They showed high photosynthetical assimilation in a considerable part of the aquatic phase, where values were reached that were comparable or even higher than those of the terrestrial phase. Anatomical, morphological and physiological adaptations supposedly are responsible for this capacit