Flexible N uptake and assimilation mechanisms may assist biological invasion by Alliaria petiolata

Abstract

Although nitrogen has historically limited terrestrial plant productivity in the northern hemisphere, accelerated industrial activity is changing the availability of N, with consequences for ecosystem properties including altered susceptibility to biological invasion. Alliaria petiolata (Bieb.) Cavara & Grande is an increasingly problematic invader in forests of eastern North America. Population growth rate of this species is especially high in N-rich habitats, and it produces a variety of N-based compounds that have been shown to interfere with the growth and reproduction of native plants. To investigate how increases and shifts in forms of N will impact A. petiolata, seedlings were transplanted to the greenhouse from the field and grown in sand culture. We applied three concentrations of N (0.25, 1 and 2 mM) using five different ratios of NH4+ and NO3− (100/0, 75/25, 50/50, 25/75, 0/100) in a crossed design to yield fifteen different treatments. Plants were measured throughout the growing season and a final harvest yielded measures of biomass and tissue quality. Plant growth increased significantly in response to increased concentration of total N. These increases were similar for all combinations of N. This flexibility in uptake ability may facilitate the invasion of this species, not only by increasing the range of habitats A. petiolata can occupy but also by enhancing N uptake that can lead to the production of secondary compounds disrupting other species’ belowground mutualisms. We suggest that this species’ ability to respond rapidly to changes in N availability, regardless of its form, may modify competitive interactions with natives and intensify its negative impacts.