Extended leaf phenology, allelopathy, and inter-population variation influence invasion success of an understory forest herb
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Extended leaf phenology (ELP) may commonly drive invasion in Eastern deciduous forests of North America. ELP may confer an advantage in competition, and may interact with other invasion factors. For example, ELP may interact with allelopathy (release of toxins) if exposure to seasonal light influences allelochemical production. Here, we examine ELP and its interaction with glucosinolate (allelochemical) production in invasive garlic mustard (Alliaria petiolata). To test ELP’s role in invasion, garlic mustard was grown in monoculture or polyculture with native species under natural and extended shade regimes. Consistent with an ELP invasion mechanism, garlic mustard survival was higher in natural shade than extended shade, although invader biomass and native responses did not differ between light treatments. While garlic mustard leaf glucosinolate concentration was higher in natural than extended shade during September of its first year, this pattern did not hold at three other time points. Stronger support for the role of ELP in driving garlic mustard invasion emerged from direct manipulation of germination phenology, with higher garlic mustard survival and biomass resulting when germination occurred earlier in the season. Analysis of allelochemical production across eight populations of garlic mustard revealed significant inter-population variation in glucosinolate responses to light availability. Overall, results of these three experiments indicate that ELP may facilitate garlic mustard’s survival in invaded communities. We did not find strong evidence for a synergistic relationship between ELP and allelopathic potential, possibly due to high levels of inter-population variation in the relationship between allelopathy and light.
KeywordsInvasion mechanism Glucosinolate Light availability Phenology Allelopathy
Thanks to Therese Burkhard and Gerald Smith for extensive field and laboratory assistance throughout the duration of these experiments, and to Stephanie Dickinson of the Indiana University Statistical Consulting Center for assistance with data analysis. Thanks to Richard Lankau for contributing garlic mustard seed of known allelopathic potential that was used in establishing and verifying glucosinolate analysis protocols. Thanks to NSF DEB-1310750 Doctoral Dissertation Improvement Grant, Sigma Xi Grant in Aid of Research, Indiana Native Plant and Wildflower Society, Indiana Academy of Sciences Senior Research Grant, the Indiana University Department of Biology, and contributors to the #SciFund Challenge project ‘Alien Invaders: Armed and Dangerous’ for financial support for these experiments.
Conflict of interest
The authors declare that they have no conflict of interest.
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