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Free keywords:
floodplain forest; varzea; igapo; seed germination; seedling establishment; survival strategies; submergence; morphological adaptations
Abstract:
Plants are subjected to extended periods of waterlogging and submersion in the floodplains of Central Amazonia. Several adaptations and growth strategies allow them to survive. In this study, germination and seedling growth of seeds of six tree species from nutrient-rich varzea and six from nutrient-poor igapo were analysed in the Amazon Research Institute (INPA) in Manaus, Brazil. Germination rates and duration were lower in species from varzea than from igapo. The cotyledons opened later and had lower longevity in varzea, where the environment provides sufficient nutrients to the establishing seedling and there is less need for nutrient supply by the mother plant. Species from varzea produced smaller seeds and the seedlings tended to grow less than in igapo where large-seeded species predominated. Mortality of waterlogged and submerged seedlings was low in all species, except in submerged seedlings of Senna reticulata. Leaf production and shedding was continuous in the varzea species. but in the species from igapo leaves had higher longevity. An explanation for the dynamic leaf phenology in varzea might be that this is an adaptation against the high sediment load which covers the leaves and impedes photosynthetic activity. Morphological adaptations to flooding (adventitious roots, lenticels, stem hypertrophy) occurred only in waterlogged seedlings from varzea species, maybe as a consequence of the oxygen deficiencies in the rhizosphere caused by the high plant productivity and decomposition in this ecosystem. The production of morphological adaptations might be limited by the low nutrient availability in igapo. The differences in germination and growth in varzea and igapo may be responses to the different nutrient availabilities in the two ecosystems and thus represent different survival strategies. In varzea, morphological adaptations which require high nutrient supply allow the plants to maintain growth and photosynthetic activity at high levels, even during waterlogging. Igapo species have a fast initial growth and constant leaf production, investing in high seed mass, leaf sclerophylly and reduced leaf loss. They tend to remain in a state of rest during flooding
