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Garlic mustard is a well-known invader of deciduous forests of North America, yet the influence of environmental factors on garlic mustard allelochemical production is not well understood. Three experiments were conducted to detect interactions between one garlic mustard allelochemical (glucosinolate) production and light availability. First, to detect patterns of glucosinolate production across a natural light gradient, leaves and roots of mature plants and first-year rosettes were sampled in patches ranging from 100 to 2 % of full sun within an Indiana forest. Second, to determine whether genetic variation drives observed correlations between glucosinolate content and light, seed collected across light gradients within six sites was grown in a common garden and glucosinolate production was measured. Finally, to understand whether local adaptation occurred in garlic mustard's response to light, seed collected from defined light environments across six sites was grown under four light treatments. Results of the field sampling showed that mature plants' root glucosinolate content was elevated in high compared to low light. In the common garden experiment, however, there was no correlation between light availability at seed origin and constitutive glucosinolate content. Additionally, in the common light treatments, there was no evidence for local adaptation to light environment. Overall, the results indicate that plasticity in response to light, not genetic variation among plants growing in different light environments, generates correlations between glucosinolate content and light in the field. Since mature garlic mustard populations in high light may exhibit increased glucosinolate content, it makes them potential targets for management. [ABSTRACT FROM AUTHOR]

Specialized metabolites in plants influence their interactions with other species, including herbivorous insects, which may adapt to tolerate defensive phytochemicals. The chemical arsenal of Alliaria petiolata (garlic mustard, Brassicaceae) includes the glucosinolate sinigrin and alliarinoside, a hydroxynitrile glucoside with defensive properties to glucosinolate-adapted specialists. To further our understanding of the chemical ecology of A. petiolata, which is spreading invasively in North America, we investigated the metabolite profile and here report a novel natural product, petiolatamide, which is structurally related to sinigrin. In an extensive study of North American populations of A. petiolata, we demonstrate that genetic population differences as well as developmental regulation contribute to variation in the leaf content of petiolatamide, alliarinoside, sinigrin, and a related glycoside. We furthermore demonstrate widely different metabolic fates of these metabolites after ingestion in the glucosinolate-adapted herbivore Pieris rapae, ranging from simple passage over metabolic conversion to sequestration. The differences in metabolic fate were influenced by plant β-glucosidases, insect-mediated degradation, and the specificity of the larval gut transport system mediating sequestration. [ABSTRACT FROM AUTHOR]

Studies of allelopathy in terrestrial systems have experienced tremendous growth as interest has risen in describing biochemical mechanisms responsible for structuring plant communities, determining agricultural and forest productivity, and explaining invasive behaviors in introduced organisms. While early criticisms of allelopathy involved issues with allelochemical production, stability, and degradation in soils, an understanding of the chemical ecology of soils and its microbial inhabitants has been increasingly incorporated in studies of allelopathy, and recognized as an essential predictor of the outcome of allelopathic interactions between plants. Microbes can mediate interactions in a number of ways with both positive and negative outcomes for surrounding plants and plant communities. In this review, we examine cases where soil microbes are the target of allelopathic plants leading to indirect effects on competing plants, provide examples where microbes play either a protective effect on plants against allelopathic competitors or enhance allelopathic effects, and we provide examples where soil microbial communities have changed through time in response to allelopathic plants with known or potential effects on plant communities. We focus primarily on interactions involving wild plants in natural systems, using case studies of some of the world's most notorious invasive plants, but we also provide selected examples from agriculturally managed systems. Allelopathic interactions between plants cannot be fully understood without considering microbial participants, and we conclude with suggestions for future research. [ABSTRACT FROM AUTHOR]

Invasive species can benefit from altered species interactions in their new range, and by interfering with species interactions among native competitors. Since exotic invasions are generally studied at the species level, relatively little is known about intraspecific variation in the traits that determine an invader's effect on native species. Alliaria petiolata is a widespread and aggressive invader of forest understories that succeeds in part by interfering with mutualistic interactions between native plants and soil fungi. Here, I show that the impact of A. petiolata on soil microbial communities varied among individuals due to variation in their allelochemical concentrations. The differential impacts translated into varied effects on native tree growth, partly because A. petiolata's allelochemicals preferentially affected the most mutualistic fungal taxa. These results highlight the importance of considering the spatial and temporal variation in an invasive species' impacts for understanding and managing the invasion process. [ABSTRACT FROM AUTHOR]

Forests throughout the US are invaded by non-native invasive plants. Rural housing may contribute to non-native plant invasions by introducing plants via landscaping, and by creating habitat conditions favorable for invaders. The objective of this paper was to test the hypothesis that rural housing is a significant factor explaining the distribution of invasive non-native plants in temperate forests of the Midwestern US. In the Baraboo Hills, Wisconsin, we sampled 105 plots in forest interiors. We recorded richness and abundance of the most common invasive non-native plants and measured rural housing, human-caused landscape fragmentation (e.g. roads and forest edges), forest structure and topography. We used regression analysis to identify the variables more related to the distribution of non-native invasive plants (best subset and hierarchical partitioning analyses for richness and abundance and logistic regression for presence/absence of individual species). Housing variables had the strongest association with richness of non-native invasive plants along with distance to forest edge and elevation, while the number of houses in a 1 km buffer around each plot was the variable most strongly associated with abundance of non-native invasive plants. Rhamnus cathartica and Lonicera spp. were most strongly associated with rural housing and fragmentation. Berberis thumbergii and Rosa multiflora were associated with gentle slopes and low elevation, while Alliaria petiolata was associated with higher cover of native vegetation and stands with no recent logging history. Housing development inside or adjacent to forests of high conservation value and the use of non-native invasive plants for landscaping should be discouraged. [ABSTRACT FROM AUTHOR]

The purpose of this study was to test competitive and allelopathic effects of invasive garlic mustard on American ginseng ( Panax quinquefolius) seedlings under natural conditions. For comparative purposes, we also examined the potential effects of the native striped violet ( Viola striata). In order to partition effects of resource competition and chemical suppression via allelopathy, field soils were amended with activated carbon or left unamended. Activated carbon positively affected ginseng growth as well as biomass of competitors. Ginseng mortality tended to increase with garlic mustard presence, though activated carbon alleviated this response. Garlic mustard had no significant effect on ginseng seedling growth, while striped violet suppressed shoot length in the absence of activated carbon. Our results showed a surprising effect of activated carbon on plant growth, a potential allelopathic effect of the native striped violet and suggest that newly invaded ginseng populations with low densities of garlic mustard may be able to withstand its effects. However, recruitment within invaded populations may decline. [ABSTRACT FROM AUTHOR]