Resistance to complete submergence in Rumex species with different life histories: the influence of plant size and light

Resistance to complete submergence was tested in three Rumex species that o ccur in the Dutch river forelands. The species differ in both habitat and l ife history characteristics. The annual or biennial R. maritimus and the bi ennial or short lived perennial R. palustris grow on frequently flooded mud flats of low elevation, while the perennial R. thyrisflorus can be found o n dykes and river dunes that are seldom flooded. The flooding characteristi cs of the habitats of the three species were determined. These data were us ed to design experiments to determine the survival and biomass development of the three species during submergence and the influence of plant size and light level on these parameters. It was shown in all three species that pl ants submerged during daytime were much more resistant to flooding than tho se submerged at night. This is most probably due to the generation of oxyge n or carbohydrates by underwater photosynthesis. Mature plants of the three species showed higher survival after submergence than juvenile plants, whi ch might be caused by higher carbohydrate levels in the taproots of mature plants. In addition, the three species clearly differed in survival and bio mass development during submergence. Rumex thyrsiflorus, the species least subjected to flooding, is least tolerant to complete submergence. Rumex mar itimus, which can avoid the floods Ly having a short life cycle, is less to lerant to submergence than R. palustris, which has to survive the floods as a vegetative plant. It was noted that some plants that survived the floodi ng period itself, still died in the following period of drained conditions, possibly due to post-anoxic injury.