Testing native plants for multifunctional infiltration swales: Effects of substrate amendments and flooding

Climate change causes increased temperatures and more variable precipitation patterns. Resulting heavy rainfall leads to localized stormwater that is further enhanced by sealed surfaces in urban areas. Cities need to adapt to such events, and one step in this direction are vegetated infiltration swales, which help mitigate peak runoff volumes during heavy rainfall events by improved urban green infrastructure. To fully exploit their multifunctionality, functional substrates must be combined with appropriate vegetation. As such systems are not yet fully understood, we aimed to find suitable plant–substrate combinations to increase multifunctionality of infiltration swales. Thus, we tested monocultures of four herbaceous plant species native to central Europe on substrates amended with sand, biochar, or both for their responses to waterlogging in a greenhouse experiment. The congeneric pairs of species that were adapted to mesic or wet conditions showed contrasting results. Wetland plants suffered less from flooding and were less susceptible to changes in substrate. Meanwhile, plants from mesic conditions responded negatively to flooding and showed interactive reactions to substrate–flooding combinations. These findings indicate that wetland plants are better suited to the frequently waterlogged conditions of infiltration swales, particularly when functionality requires a substrate type that does not fully align with plant needs. • The contrasting forb species survive repeated waterlogging on different substrates. • Wetland species are less susceptible to soil composition and flooding than mesic congeners. • Plant selection based on native habitats can be recommended for infiltration swales.