Plants in central Amazonian floodplains are subjected to waterlogging or complete
submersion for 50-270 days every year. Most trees have growth reductions, 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 trigger the changes in phenology, growth and metabolism
of the plants has not yet been established. The aim of this study was to analyse the
extent to which waterlogging was directly responsible for morphological, phenological
and physiological changes in floodplain seedlings. In two flooding experiments performed
at different times of the year, the effects of waterlogging, submersion and drought
were tested in seedlings of six species with different growth strategies. One experiment
was performed in the period of highest precipitation and rising river levels, and
a second experiment in the period of highest river levels and the onset of the period
of lowest precipitation. All results were comparable in the two experiments, and the
morphological, phenological and physiological responses were linked to the treatments.
Height growth and new leaf production were not severely affected in the waterlogged
seedlings. All waterlogged plants produced adventitious roots, lenticels 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 control plants, showing a high ability to compensate
the period of rest induced by submergence. Only the three deciduous species subjected
to waterlogging showed a different phenological behaviour in the two experiments,
perhaps related to genetically fixed phenological rhythms which are synchronous to
those of adult trees in the field.