Consecutive submergence and de-submergence both impede growth of a riparian plant during water level fluctuations with different frequencies

Repeated exposure to submergence and de-submergence may induce acclimation in plants growing in riparian areas. However, the effect of each consecutive submergence and de-submergence event has not been evaluated separately. We subjected a riparian species Alternanthera philoxeroides to two different fluctuation frequencies: low fluctuation frequency (LFF) and high fluctuation frequency (HFF). Consecutive submergence and de-submergence had comparable negative effects on growth of A. philoxeroides, while they respectively down- and up-regulated photosynthetic electron transport in both LFF and HFF. The submergence effects on growth were significantly smaller in the 2nd cycle than in the 1 st cycle of LFF, suggesting reduced tissue loss in the 2nd cycle as a result of acclimation. In HFF, the growth of A. philoxeroides was more strongly suppressed than in LFF. During de-submergence, biomass increased in both control and de-submerged plants in LFF, whereas growth recovery was not always seen in HFF. At the end of the experiment, the treatment plants in HFF had only ∼50% biomass of the corresponding plants in LFF. Although HFF enhances tissue loss during submergence and thus impairs growth recovery more strongly during de-submergence than LFF, both LFF and HFF induced photosynthetic, photoprotective or growth acclimation in A. philoxeroides.