The impact of a biological invasion on native communities is expected to be uneven across invaded landscapes due to differences in local abiotic conditions, invader abundance, and traits and composition of the native community. One way to improve predictive ability about the impact of an invasive species given variable conditions is to exploit known mechanisms driving invasive species' success. Invasive plants frequently exhibit allelopathic traits, which can be directly toxic to plants or indirectly impact them via disruption of root symbionts, including mycorrhizal fungi. The indirect mechanism – mutualism disruption – is predicted to impact plants that rely on mycorrhizas but not affect non‐mycorrhizal plant species. To assess whether invader‐driven mutualism disruption explains observed changes in native plant communities, we analyzed long‐term (1998–2018) plant cover data from forest plots across the state of Illinois. We evaluated native plant communities experiencing a range of abundance of invasive allelopathic garlic mustard
The mechanisms causing invasive species impact are rarely empirically tested, limiting our ability to understand and predict subsequent changes in invaded plant communities. Invader disruption of native mutualistic interactions is a mechanism expected to have negative effects on native plant species. Specifically, disruption of native plant‐fungal mutualisms may provide non‐mycorrhizal plant invaders an advantage over mycorrhizal native plants. Invasive
- NSF-PAR ID:
- 10480368
- Publisher / Repository:
- Wiley Periodicals LLC
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 102
- Issue:
- 1
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Alliaria petiolata and varying environmental conditions. Consistent with the mutualism disruption hypothesis, we showed that as garlic mustard abundance increased over time in 0.25 m2sampling quadrats, the abundance of mycorrhizal plant species decreased, but non‐mycorrhizal plant species did not. Over space and time, garlic mustard abundance predicted plant abundances and diversity at the quadrat level, but this relationship was not present at a larger scale when quadrats were aggregated within sites. Garlic mustard's impact on the plant community was highly localized, yet it was as important as abiotic variables for predicting local plant diversity. We showed that garlic mustard abundance was a key predictor of patterns of plant diversity across invasion intensity and environmental heterogeneity in a way that is consistent with mutualism disruption. Our work indicates that the mutualism disruption hypothesis can provide generalizable predictions of the impacts of allelopathic invasive plants that are evident at a broad spatial scale. -
Introduction Alliaria petiolata (garlic mustard), an invasive forest herb in North America, often alters nutrient availability in its non-native ecosystems, but the mechanisms driving these changes have yet to be determined. We hypothesized three potential mechanisms through which garlic mustard could directly influence soil nitrogen (N) cycling: by increasing soil pH, by modifying soil microbial community composition, and by altering nutrient availability through litter inputs. Materials and methods To test these hypotheses, we evaluated garlic mustard effects on soil pH and other soil properties; fungal and prokaryotic (bacterial and archaeal) community composition; and soil N cycling rates (gross N mineralization and nitrification rates, microbial N assimilation rates, and nitrification- versus denitrification-derived nitrous oxide fluxes); and we assessed correlations among these variables. We collected soil samples from garlic mustard present, absent, and removed treatments in eight forests in central Illinois, United States, during the rosette, flowering, and senescence phenological stages of garlic mustard life cycle. Results We found that garlic mustard increased soil pH, altered fungal and prokaryotic communities, and increased rates of N mineralization, nitrification, nitrification-derived net N2O emission. Significant correlations between soil pH and microbial community composition suggest that garlic mustard effects on soil pH could both directly and indirectly influence soil N cycling rates. Discussion Correspondence of gross rates of N mineralization and nitrification with microbial community composition suggest that garlic mustard modification of soil microbial communities could directly lead to changes in soil N cycling. We had expected that early season, nutrient-rich litter inputs from mortality of young garlic mustard could accelerate gross N mineralization and microbial N assimilation whereas late season, nutrient poorer litter inputs from senesced garlic mustard could suppress N mineralization, but we did not observe these patterns in support of the litter input mechanism. Together, our results elucidate how garlic mustard effects on soil pH and microbial community composition can accelerate soil N cycling to potentially contribute to the invasion success of garlic mustard.more » « less
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Exotic invasive plant species alter ecosystems and locally extirpate native plant species, and by doing so alter community structure. Changes in community structure may be particularly important if invaders promote species with certain traits. For example, the positive effects of most invaders on soil fertility may promote species with weedy traits, whether native or not. We examined the effects of two co-occurring Prosopis congeners, the native P. cineraria and the exotic invader P. juliflora, on species identified as “agricultural weeds” and species that were not agricultural weeds in the United Arab Emirates. When compared to plots in the open, P. cineraria canopies were associated with lower richness and density of non-weeds while having no impact on agricultural weed species. In contrast, there was lower richness and densities of non-weeds under canopies of P. juliflora, but higher densities of agricultural weeds than in the open surrounding the canopies. These patterns associated with Prosopis congeners and understory plant community composition might be due to the much higher litter deposition, if litter is inhibitory, and shallow root biomass under P. juliflora, or the different soil properties that corresponded with the two Prosopis canopies. In general, soils contained more nitrogen under P. juliflora than P. cineraria, and both understories were more fertile than soil in the open. Our results suggest that evolutionary history may play a role in how exotic invasive species may select for some traits over others in plant communities, with an exotic invader potentially creating reservoirs of agricultural weeds.more » « less
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null (Ed.)Abstract The impacts of invasive species on biodiversity may be mitigated or exacerbated by abiotic environmental changes. Invasive plants can restructure soil fungal communities with important implications for native biodiversity and nutrient cycling, yet fungal responses to invasion may depend on numerous anthropogenic stressors. In this study, we experimentally invaded a long-term soil warming and simulated nitrogen deposition experiment with the widespread invasive plant Alliaria petiolata (garlic mustard) and tested the responses of soil fungal communities to invasion, abiotic factors, and their interaction. We focused on the phytotoxic garlic mustard because it suppresses native mycorrhizae across forests of North America. We found that invasion in combination with warming, but not under ambient conditions or elevated nitrogen, significantly reduced soil fungal biomass and ectomycorrhizal relative abundances and increased relative abundances of general soil saprotrophs and fungal genes encoding for hydrolytic enzymes. These results suggest that warming potentially exacerbates fungal responses to plant invasion. Soils collected from uninvaded and invaded plots across eight forests spanning a 4 °C temperature gradient further demonstrated that the magnitude of fungal responses to invasion was positively correlated with mean annual temperature. Our study is one of the first empirical tests to show that the impacts of invasion on fungal communities depends on additional anthropogenic pressures and were greater in concert with warming than under elevated nitrogen or ambient conditions.more » « less
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Abstract The direct role of non‐native plant invaders in driving negative population‐ and community‐level processes of native species has been recently questioned. Addressing this controversy requires determining quantitatively if invaders negatively affect native population fitness. Because the invasion of non‐natives often coincides with other anthropogenic stressors, experiments that partition the putative impact of non‐natives from other known stressors and assess their potential synergies are required. While many studies have examined the effects of non‐natives on components of native plant performance, studies that decompose the net fitness effects of non‐natives from other anthropogenic stressors on population growth rate are lacking.
We used 6 years of detailed demographic data to parameterize a size‐dependent integral projection model to examine the individual and combined effects of an allelochemical‐producing invader (
Alliaria petiolata ) and an overabundant ungulate herbivore(Odocoileus virginianus ) on the population dynamics of an understory perennial (Trillium erectum ).We show that
Alliaria consistently and negatively affects the population dynamics ofTrillium . Specifically, this invader reduces native population growth rate and alters the size distribution of the population at equilibrium.Alliaria also works in concert with the known negative impacts of overabundant white‐tailed deer, illustrating the additive effects of anthropogenic stressors on native plant dynamics.Synthesis .Alliaria's effects on vital rates differed in magnitude and sign across the native's life cycle, highlighting the importance of detailed demographic analyses. Our study provides novel empirical support for the claim that non‐native invasive species can significantly and directly reduce the fitness of native plants.
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- Journal Article:
- https://doi.org/10.1002/ecy.3201
