Flooding tolerance: suites of plant traits in variable environments

Flooding regimes of different depths and durations impose selection pressures for various traits in terrestrial wetland plants. Suites of adaptive traits for different flooding stresses, such as soil waterlogging (short or long duration) and full submergence (short or long duration-shallow or deep), are reviewed. Synergies occur amongst traits for improved internal aeration, and those for anoxia tolerance and recovery, both for roots during soil waterlogging and shoots during submergence. Submergence tolerance of terrestrial species has recently been classified as either the Low Oxygen Quiescence Syndrome (LOQS) or the Low Oxygen Escape Syndrome (LOES), with advantages, respectively, in short duration or long duration (shallow) flood-prone environments. A major feature of species with the LOQS is that shoots do not elongate upon submergence, whereas those with the LOES show rapid shoot extension. In addition, plants faced with long duration deep submergence can demonstrate aspects of both syndromes; shoots do not elongate, but these are not quiescent, as new aquatic-type leaves are formed. Enhanced entries of O-2 and CO2 from floodwaters into acclimated leaves, minimises O-2 deprivation and improves underwater photosynthesis, respectively. Evolution of 'suites of traits' are evident in wild wetland species and in rice, adapted to particular flooding regimes.