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Growing Greener

Chemical Warfare from Invasive Plants

April 8, 2026·29 min·1 clip
Dr. Susan Calise explains why 70% of land plants depend on AM fungi and why that matters for invasives.
1. Growing Greener and Tom Christopher center this conversation on the 2021 Biological Invasion paper "Allelopathy is Pervasive in Invasive Plants," which Dr. Susan Calise discusses from the University of Tennessee, Knoxville. 2. Tom Christopher hosts the show, and Dr. Susan Calise is a research professor and former head of ecology and evolutionary biology, which gives her firsthand experience with invasive species research. 3. Calise's core claim is that invasive plants can use "novel weapons" in new habitats, with soil chemicals that suppress native plants and disrupt AM fungi. 4. She says allelopathy can be direct, by reducing germination and seedling survival, or indirect, by damaging arbuscular mycorrhizal fungi that supply water and nutrients. 5. Calise uses black walnut and its chemical "juglone" as a native example, while stressing that the paper focuses on invasive species rather than native allelopathy. 6. She describes two main release pathways for invasive chemicals: root exudation into soil and leaf litter decomposition that releases compounds as leaves die. 7. The paper's evidence base comes from a literature compilation, and Calise corrects the transcript's numbers to 72% of 113 tested invasive species showing allelopathy. 8. She names Japanese knotweed, garlic mustard, and Japanese honeysuckle as examples of invaders with strong allelopathic effects and visible monocultures. 9. Calise also explains that plants like trillium can take 17 to 20 years to flower, which makes evolutionary adaptation to new chemicals slow compared with invading species. 10. Gardeners, ecologists, and native-plant growers interested in invasive species and soil chemistry.

As heard by us

A clear look at how soil-released chemicals may help many invasive plants outcompete native plants.

Tom Christopher's conversation with University of Tennessee researcher Susan Calise gives soil ecology a surprisingly tangible edge. Calise explains how invasive plants can release chemicals into the soil that harm native plants and the soil-borne organisms supporting them.

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Why you'd press play

You'll discover how invasive plants can outcompete native neighbors through chemicals released into the soil.

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