Abstract
The widespread invasion of the nonmycorrhizal biennial plant, Alliaria petiolata in North America is hypothesized to be facilitated by the production of novel biochemical weapons that suppress the growth of mycorrhizal fungi. As a result, A. petiolata is expected to be a strong competitor against plant species that rely on mycorrhizal fungi for nutrient uptake services. If A. petiolata is also a strong competitor for soil resources, it should deplete nutrients to levels lower than can be tolerated by weaker competitors. Because the negative effect of losing the fungal symbiont for mycorrhizal plants is greatest when nutrients are low, the ability of A. petiolata to simultaneously suppress fungi and efficiently take up soil nutrients should further strengthen its competitive ability against mycorrhizal plants. To test this hypothesis, we grew 27 mycorrhizal tree, forb and grass species that are representative of invaded habitats in the absence or presence of competition with A. petiolata in soils that had previously been experimentally planted with the invader or left as a control. A history of A. petiolata in soil reduced plant available forms of nitrogen by >50% and phosphorus by 17% relative to control soil. Average mycorrhizal colonization of competitor species was reduced by >50% in A. petiolata history versus control soil. Contrary to expectations, competition between A. petiolata and other species was stronger in control than history soil. The invader suppressed the biomass of 70% of competitor species in control soil but only 26% of species in history soil. In addition, A. petiolata biomass was reduced by 56% in history versus control soil, whereas the average biomass of competitor species was reduced by 15%. Thus, our results suggest that the negative effect of nutrient depletion on A. petiolata was stronger than the negative effect of suppressing mycorrhizal colonization on competitor species. These findings indicate that the inhibitory potential of A. petiolata on competitor species via mycorrhizal suppression is not enhanced under nutrient limitation.
Highlights
Invasions by exotic species are common and can negatively influence the structure and function of invaded communities and ecosystems (Pimental et al, 2000)
On a growth form basis, trees (−38%, P = 0.01), forbs (−62%, P < 0.000001) and grasses (−56%, P < 0.000001) were all suppressed by A. petiolata in control soil, whereas the biomass of forbs (−32%, P < 0.000001) and grasses (−14%, P = 0.007), but not trees (P = 0.228), was significantly reduced by competition in the A. petiolata history soil (Fig. 1, insets)
Our results indicate that A. petiolata is a strong competitor against a range of common mycorrhizal grassland, old field and forest species in soils which had no previous history with its conspecifics, but contrary to expectation, this competitive advantage weakens in soil with a history of conspecific growth
Summary
Invasions by exotic species are common and can negatively influence the structure and function of invaded communities and ecosystems (Pimental et al, 2000). Numerous mechanisms have been identified to explain successful invasions (Catford, Jansson & Nilsson, 2009; Gurevitch et al, 2011). Recent reviews suggest that successful invasions rarely occur because of a single mechanism (Catford, Jansson & Nilsson, 2009; Gurevitch et al, 2011). The efficacy of a particular mechanism may depend on ecological context, where differences in resource availability and the functional attributes of resident species can either facilitate or increase resistance to invasion (Funk et al, 2008). Multiple mechanisms could act synergistically, as observed in situations where invasion is facilitated by both competitive suppression of resident species and reduced palatability to herbivores (Lau & Schultheis, 2015). Simultaneous empirical assessments of multiple causes of invasion, are infrequent (Zheng et al, 2015)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
