Salt intrusion in tidal wetlands: European willow species tolerate oligohaline conditions

Abstract

Tidal wetlands experience salt intrusion due to the effects of climate change. This study clarifies that the European flood plain willows species Salix alba and Salix viminalis tolerate oligohaline conditions. Salix alba L. and Salix viminalis L. are distributed on flood plains up to transitional waters of the oligohaline to the mesohaline estuarine stretch in temperate climates. They experience spatial and temporal variations in flooding and salinity. In the past, willows dominated the vegetation above the mean high water line, attenuated waves and contributed to sedimentation. In recent centuries, human utilization reduced willow stands. Today, the Elbe estuary – a model system for an estuary in temperate zones – exhibits increasing flooding and salinity due to man-induced effects and climatic changes. Willows were described as having no salinity tolerance. In contrast, our soil water salinity measurements at willows in tidal wetlands prove that mature Salix individuals tolerate oligohaline conditions. To assess immature plant salinity tolerance, we conducted a hydroponic greenhouse experiment. Vegetative propagules originating from a freshwater and an oligohaline site were treated in four salinities. Related to growth rates and biomass production, we found interspecific similarities and a salinity tolerance up to salinity 2. Vitality and chlorophyll fluorescence indicated an acclimation of Salix viminalis to oligohaline conditions. We conclude, that the survival of S. alba and S. viminalis and the restoration of willow stands in estuarine flood plains – with regard to wave attenuation and sedimentation – might be possible, despite increasing salinity in times of climate change.