Hale, Alison , Kalisz, Susan .
Mutualism disruption as a mechanism of invasion? Allelopathic invader drives declines in native plant physiology and resource allocation via AMF disruption.
Approximately 70-90% of all land plants participate in mutualisms with arbuscular mycorrhizal fungi (AMF). The basis for the mutualism is a two-way exchange of resources: the plant provides the AMF with carbon, while the AMF supply the plant with mineral nutrients and water absorbed from the soil via external hyphae. Worldwide, most forest understory herbs depend heavily on AMF-derived soil resources for physiological function. However, across forests in eastern North America, the invasion of garlic mustard (Alliaria petiolata), a species with allelopathic effects on AMF, could pose a significant threat to the function of the plant-AMF mutualism for native understory herbs. If garlic mustardís allelochemicals kill AMF hyphae in the soil, then we predict that native plant physiological function will decline, overall resource acquisition will be diminished and resource allocation patterns will be altered. To test this hypothesis, we conducted a greenhouse pot experiment with the AMF-dependant, native forest herb, Maianthemum racemosum (Liliaceae). We treated the soil either with fungicide (mimicking the predicted effects of garlic mustard), or leaves from garlic mustard or Hesperis matronalis, an allelochemical-free relative of garlic mustard. Leaf gas exchange was measured weekly from June-September, and plants were harvested periodically to assess the pattern of allocation to storage, growth, and reproduction.
We found that garlic mustard treated plants expressed significantly reduced photosynthetic rates compared to the dameís rocket treatment. Further, garlic mustard treated plants did not differ from fungicide treated plants. To determine whether the observed photosynthetic declines were due to the loss of AMF-derived mineral nutrients or water, we assessed plant carboxylation efficiency. Low carboxylation efficiency indicates a loss of photosynthetic machinery due to nutrient stress. Plants in the garlic mustard treatment had significantly lower carboxylation efficiency than plants in the dameís rocket treatment. Thus, the loss of AMF-derived mineral nutrients (e.g. nitrogen, phosphorus) likely explains the declines in photosynthesis. We also found that garlic mustard treated plants had significantly reduced concentrations of stored carbohydrate, diminished root growth, and fewer clonal buds than control plants, which together can reduce individualís fitness and long-term survival. Overall, our results demonstrate that garlic mustardís impacts on the plant-AMF mutualism can severely alter native plant physiological function and allocation patterns. We propose that the disruption of native plant mutualisms may be a widespread mechanism behind successful ecosystem invasion of exotic species.
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1 - University of Pittsburgh, Department of Biological Sciences, 4249 Fifth Avenue, Pittsburgh, PA, 15260, USA
2 - University Of Pittsburgh, Department Of Biological Sciences, 4249 Fifth Avenue, 205 Clapp Hall, Pittsburgh, PA, 15260, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 9th, 2012
Time: 9:30 AM