Flood tolerance in common buckthorn (Rhamnus cathartica)

Rhamnus cathartica is a Eurasian shrub that has invaded woodland habitats of eastern North America. While historically known from more mesic habitats, it is often found in wetland habitats in Illinois, Minnesota, and Wisconsin, USA. This study assessed R. cathartica's growth, architecture, and biomass allocation across multiple flooding treatments representing a soil moisture gradient spanning upland (mesic soil moisture) to wetland habitats (saturated within 30 cm of the soil surface, periodic flooding, and permanently flooded conditions) for two age classes of saplings of R. cathartica. Our results on plant growth patterns under these treatments show that young R. cathartica saplings were able to tolerate saturated soil conditions, while old saplings were able to tolerate periodic flooding. Allocation of biomass to above- versus below-ground tissues showed that both young and old saplings have similar biomass allocation patterns in relation to soil moisture treatments. Collectively, our results suggest that R. cathartica exhibits tolerance to periodic flooding, and that this may partly explain its invasion of certain wetland habitats in North America.