Morphological and physiological adjustments to waterlogging and drought inseedlings of Amazonian floodplain trees

Plants in central Amazonian floodplains are subjected to waterlogging or co mplete submersion for 50-270 days every year. Most trees have growth reduct ions, photosynthetic activity can be reduced for some weeks to months, and leaf fall increases during the high-water period, but leaf flush, flowering and fruiting also occur in waterlogged plants. Whether flooding can trigge r the changes in phenology growth and metabolism of gy, the plants has not yet been established. The aim of this study was to analyse the extent to wh ich waterlogging was directly responsible for morphological, phenological a nd physiological changes in floodplain seedlings. In two flooding experimen ts performed at different times of the year, the effects of waterlogging su bmersion and drought were tested in seedlings of six species with different growth strategies. One experiment was performed in the period of highest p recipitation and rising river levels, and a second experiment in the period of highest river levels and the onset of the period of lowest precipitatio n. All results were comparable in the two experiments, and the morphologica l, phenological and physiological responses were linked to the treatments. Height growth and new leaf production were not severely affected in the wat erlogged seedlings. All waterlogged plants produced adventitious roots, len ticels and stem hypertrophy. Submersion and drought caused a state of rest, but soon after the water had receded, leaves resprouted. Five to 12 weeks after the end of submersion, the seedlings reached the height of the contro l plants, showing a high ability to compensate the period of rest induced b y submergence. Only the three deciduous species subjected to waterlogging s howed a different phenological behaviour in the two experiments, perhaps re lated to genetically fixed phenological rhythms which are synchronous to th ose of adult trees in the field.