Whole plant adaptations to fluctuating water tables

Why some plants are damaged by flooding and others are not, is not a question that can be answered by citing any one particular mechanism or sequence of events. Flood-tolerant plants like obligate aquatic species can survive inundation but differ in that they are also adapted to withstand the consequences of becoming unflooded. Flooding implies a transitory state so that when water tables drop, adapted species have to be able to survive being deprived of the physical support of flood-water as well as re-exposure to a normal air supply. A review of flooding tolerance mechanisms reveals that tolerant species combine a range of adaptations which, depending on the life strategy of the species, can play different roles in enabling intact plants to adjust to both rising and falling water levels. Flooding is also a seasonal stress with many temperate plant communities being subjected to high water tables in winter. The mechanisms that confer tolerance of winter flooding also differ from those that allow plants to grow when flooded during the growing season. This review argues therefore, that reductionist investigations, which examine isolated organs or individual processes, may not be the most suitable method to apply to understanding the complexity of reactions that are needed to survive flooding. Instead, a holistic approach is advocated which examines the reactions of whole plants to changing water levels at different seasons of the year.