FLOOD-INDUCED LEAF ELONGATION IN RUMEX SPECIES - EFFECTS OF WATER DEPTH AND WATER MOVEMENTS

Several species from the genus Rumex are found in Dutch river forelands. Species such as R. palustris Sm. from the low, frequently flooded areas are well adapted to wet conditions. Rumex species from higher and less frequently flooded sites are poorly adapted and therefore sensitive to flooding. One of;the adaptations to flooding is enhanced shoot elongation upon complete submergence, enabling plants to restore leaf-air contact, provided that the water is not too deep. This paper demonstrates the strong variation in the absolute extent of flood-induced leaf elongation among species of the genus Rumex. The effects of flooding on shoot dry and fresh weight and internal gas volumes of an elongating and a non-elongating species, R. palustris and R. acetosella L., were compared. Net water uptake in response to complete submergence was observed in the shoots of both species. Based on results presented here, we conclude that in plants of R. palustris water enters the cells and is used for cell expansion leading to petiole elongation, whereas in plants of R. acetosella at least part of the water taken up fills the intercellular gas spaces. Elongation of completely submerged Rumex plants does not vary with different depths of submergence. This was concluded from the observation that there is little effect of either hydrostatic pressure or irradiance on leaf elongation during complete submergence. However, when R. palustris plants were subjected to a changing water depth, i.e. alternate periods of complete submergence and waterlogging, they elongated less strongly than under permanent complete submergence. Water movements did not affect leaf elongation induced by submergence.