Separating Above- and Belowground Effects of Alliaria Petiolata and Lonicera Maackii on The Performance of Impatiens Capensis

Invasive plants can exert their effects on native plants through both above- and belowground mechanisms. In a fully factorial field study, we examined the effects of activated carbon addition and removal of aboveground biomass (i.e., cutting) on the survival, growth and reproduction of transplanted Impatiens capensis seedlings in habitats dominated by either Lonicera maackii (honeysuckle) or Alliaria petiolata (garlic mustard). Activated carbon can adsorb organic molecules, including potential allelochemicals. Cutting of A. petiolata increased survival and fruit production of I. capensis, while cutting of L. maackii increased survival and tended to increase fruit production. Carbon application tended to increase survival of I. capensis in A. petiolata-dominated plots, but had no effect in L. maackii-dominated plots. The effects of carbon application on growth and fruit production of I. capensis depended upon the cutting treatment in A. petiolata – dominated plots. In plots where A. petiolata was not cut, carbon application increased height and fruit production. In plots where A. petiolata was cut, carbon application decreased height and tended to decrease fruit production. Impatiens capensis tended to survive longer when in competition with A. petiolata than with L. maackii. While carbon application may benefit native plant growth in the presence of A. petiolata, the addition of activated carbon after removal of aboveground biomass, a source of both allelochemicals and light competition, may have little benefit as an understory plant restoration tool.