An invasive weed that has spread across much of the U.S. harms native maples, ashes, and other hardwood trees by releasing chemicals harmful to a soil fungus the trees depend on for growth and survival, scientists report this week in the Public Library of Science. The tree-stifling alien, garlic mustard (Alliaria petiolata), first introduced into the U.S. in the 1860s, has since spread to Canada and 30 states in the East and Midwest, with recent sightings as far west as Oregon.
While many mechanisms -- from the absence of natural predators or parasites to the disruption of long-established interactions among native organisms -- have been proposed to explain the success of invasive species, this new work is the first to show that an invasive plant harms native plants by thwarting the biological "friends" upon which they depend for growth. The work, which provides striking evidence for a unique process by which invaders harm native species, was conducted by researchers at Harvard University, the University of Guelph, the University of Montana, Purdue University, and the UFZ Centre for Environmental Research in Germany.
"While vanishing habitat caused by human activity is the number one threat to biodiversity, there is great concern over the impact of accidental and intentional dispersal of alien invasive species across the globe," says Kristina A. Stinson, a plant population biologist at the Harvard Forest, Harvard’s ecology and conservation center in Petersham, Mass. "In North America, thousands of nonnative plants and animals have become established since European settlement and many more continue to be introduced. Some alien species cause little harm, while others can become very aggressive and radically transfigure their new habitat.
"The mechanisms for this phenomenon and its potential long term impacts remain poorly understood," Stinson adds, "but one possibility is that invasive species may disrupt fragile ecological relationships that evolved over millions of years."
Stinson and her colleagues found that garlic mustard targets arbuscular mycorrhizal fungi (AMF), which form mutually beneficial relationships with many forest trees. These fungi have long filaments that penetrate the roots of plants, forming an intricate interwoven network that effectively extends the plant’s root system. AMF depend on plants for energy and plants depend on the fungi for nutrients. When tree seedlings, which depend strongly on AMF, began to decline in the presence of garlic mustard, the researchers suspected that the invasive plant might thwart this symbiotic relationship.
To test this possibility, they collected soil from five forests in Ontario dominated by four species of native hardwoods. First, the researchers tested seedlings’ ability to form mycorrhizal relationships in soil with a history of garlic mustard invasion. Three species -- sugar maple, red maple, and white ash -- had significantly less AMF root colonization and grew only about one-tenth as fast in the infested soil. Seedlings grown in sterilized, AMF-free soil taken from invaded and pest-free locations showed similar reductions, suggesting that diminished microbial activity had suppressed tree growth. Other experiments showed that adding garlic mustard extracts to soil impaired AMF colonization and seedling growth, implying that the weed uses phytochemical poisons to disrupt native plants’ mycorrhizal associations and stunt their growth.
When the study was subsequently replicated with seedlings of 16 other native plants, only the hardwoods and other woody plants were harmed by the presence of garlic mustard.
"This suggests garlic mustard invades the understory of mature forests by poisoning the allies of its main competitors," Stinson says. "By killing off native soil fungi, the appearance of this weed in an intact forest could stifle the next generation of dominant canopy trees. It could also invite other native and nonnative weedy plants that currently grow in low-AMF habitats, such as those disturbed by logging or development."
The researchers plan to study which phytochemicals in garlic mustard may kill AMF, how these chemicals interact with other beneficial soil microbes, and how plants and fungi in garlic mustard’s native European habitat coexist with the noxious species.
Steve Bradt | EurekAlert!
One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie
The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy