Contrasting Effects of Allelochemicals from Two Invasive Plants on the Performance of a Nonmycorrhizal Plant

In addition to resource competition, allelopathy is believed to contribute to the invasiveness and impact of several plant invaders of North America. In this study, we examined whether aqueous leaf extracts of Alliaria petiolata and Lonicera maackii, two invaders of deciduous forests in North America, affected growth and reproduction of a target nonmycorrhizal plant and whether effects varied across a soil fertility gradient. While nutrient addition substantially improved the performance of Arabidopsis thaliana grown in field soils in pots in a growth room, addition of A. petiolata extracts to these soils had no significant independent or interactive effects on growth or reproduction. In contrast, addition of L. maackii extracts both directly reduced growth and reproduction of A. thaliana and greatly constrained increases in growth and reproduction of A. thaliana in response to increasing nutrient availability. Use of a nonmycorrhizal target plant revealed that effects of L. maackii were independent of allelopathic effects on mycorrhizae, an effect attributed to A. petiolata in other studies.