ADAPTATIONS TO FLOODING BY TROPICAL TREES: MORPHOLOGICAL AND ANATOMICAL MODIFICATIONS
Keywords:plant ecophysiology, morphological adaptations, ethylene
Many plant communities subjected to flooding are found in tropical regions and are rich in tree species. Little is known about the flood-tolerance mechanisms these species have developed. However, studies have shown that metabolic, morphological and anatomical adaptations are all important for the survival of these plants in oxygen-deficient conditions. Lenticels hypertrophy, aerenchyma formation, stem hypertrophy and the formation of adventitious roots are among the morphological and anatomical adaptations caused by flooding. These modifications enhance the oxygenization of submerged roots, permitting sufficient energy production for survival. Ethylene, which increases markedly in flooded plants, seems to be the main hormone involved in bringing about these morphological modifications. In the case of the initiation and development of adventitious roots there is a synergism between ethylene and auxin. Broader studies are now necessary to improve the understanding of these questions because of the complexity of the responses of tropical tree species to flooding.