Effects of different nitrogen regimes on competition between Ambrosia artemisiifolia, an invasive species, and two native species, Artemisia annua and Artemisia mongolica.

Evidence suggests that increased nitrogen levels heighten exotic species’ invasiveness and reduce the competitive potential of native species. To reveal the impact of nitrogen deposition on competition between invasive and native species, we compared the growth of Ambrosia artemisiifolia, an invasive species, and two native species, Artemisia annua and Artemisia mongolica under three nitrogen regimes through replacement series experiments in a greenhouse at the Chinese Academy of Science’s Beijing Forest Station. Our results showed that heights of the three species significantly increased, but total biomass did not respond to the enhancement of nitrogen levels in monoculture plantings. When planted in mixtures, however, the heights and total biomass of some species responded to increasing nitrogen levels; Ambrosia artemisiifolia significantly increased, Artemisia annua exhibited no difference, and Artemisia mongolica first increased and then decreased with the increase of nitrogen levels. The growth response of Ambrosia artemisiifolia led to a competitive advantage over two native species. The dynamics of this competition differed at different 4 生 物 多 样 性 Biodiversity Science 第 20 卷 nitrogen levels: Ambrosia artemisiifolia was a weaker competitor than native species at low level of nitrogen availability, but was a stronger competitor under high nitrogen level. Moreover, the competitive effects of Ambrosia artemisiifolia on Artemisia annua were stronger than on Artemisia mongolica. Nitrogen addition significantly enhanced the competitive ability of Ambrosia artemisiifolia and altered the competition relationship between these species, tipping the scales in favor of the Ambrosia artemisiifolia. Our study indicated that nitrogen deposition associated with global change may facilitate the invasion of Ambrosia artemisiifolia, and may enhance the vulnerability of native communities to invasion.