In drama, the uninvited visitor is a common plot device. Everyone is getting along swimmingly until a new character arrives and upsets the apple cart. Things quickly fall apart.
Garlic mustard, a tall weed native to Europe that was introduced to the United States in the late 1800's, is a bit like that uninvited visitor. Researchers have found that it disrupts a healthy relationship between hardwood tree seedlings and soil fungi, with results that can be disastrous for a forest.
Like other scientists, Kristina A. Stinson, who studies invasive plants as a research associate at the Harvard Forest, Harvard's ecology and conservation research center in Petersham, Mass., had noticed that native trees suffered in the presence of garlic mustard. "We thought their dependence on native fungi might play a role," Dr. Stinson said.
Many plants make use of arbuscular mycorrhizal fungi, which form an elaborate network of filaments throughout the soil. These fungi are a diverse group, but they all have one thing in common: they help plants take up nutrients from the soil, getting carbon in return.
Garlic mustard is a member of the mustard family, "one of the very few families that do not need to associate with mycorrhizal fungi at all," Dr. Stinson said. These species produce chemicals that have antifungal properties. Native mustards have been around long enough, she suggested, that the mycorrhizal fungi have learned to live with them. But the fungi haven't had time to adapt to garlic mustard. "It basically is killing off the fungi," she said.
In a study using soils from a forest in Ontario, Dr. Stinson and colleagues found that sugar maple and other hardwood seedlings grew much slower when the soil came from an area infested with garlic mustard than from a mustard-free area. The findings are published in the journal Public Library of Science Biology.
In studying invasive species, scientists often see a direct effect. Invasive cane toads in Australia, for example, wipe out snakes and other predators that try to eat them. But garlic mustard displays a mechanism that, so far at least, appears to be unique. "It's really a demonstration of how 'the enemy of my friend is also my enemy,' " Dr. Stinson said. By killing fungi, "it's disrupting this longstanding native mutualism."
Garlic mustard has now spread through 30 states, from Maine to Oregon, and into Canada. "When this plant shows up in a forest, the tree species themselves that become the canopy are most at risk," Dr. Stinson said. "That could have tremendous impact by changing the composition of the forest."
While the effect might not be immediate, it will occur nonetheless. "Our experiment was on seedlings," Dr. Stinson said. "But those are the future generations of forests."
Salty Logs
Modern humans may consume too much sodium, but modern gorillas often find it hard to get enough. Tropical soils tend to be deficient in the mineral and, as a result, these and other forest-dwelling primates don't get much in the plants they eat.
So they supplement their diet in different ways. Lowland gorillas, for instance, are known to hang out in swampy areas in forest clearings where there are more sodium-rich plants. But mountain gorillas have been found to have a stranger source of sodium: rotting wood.
In addition to their regular diet of leaves, stems, bark and fruits, mountain gorillas for years have been observed to eat decayed stumps and logs. Other primates, including chimpanzees and mountain monkeys, are known to eat them, too.
Rotting wood doesn't have much protein or sugar, so the behavior puzzled. Jessica M. Rothman and her colleagues at Cornell University set out to see if there was a nutritional reason for it. They studied mountain gorillas in the Bwindi Impenetrable National Park in Uganda.
As reported last week in the journal Biology Letters, the researchers found that the gorillas ate decayed wood at least once a month. The pieces eaten contained much higher amounts of sodium than the usual components of their diet, and logs and parts of stumps that the gorillas avoided had far less sodium than those that were consumed.
Bad for the Birds?
Most of the debate over genetically modified crops focuses on concerns about food safety and the potential effect of transgenic material on the environment.
But researchers in Britain have looked at a much narrower issue regarding the growing of herbicide-tolerant G.M. crops: their effect on partridges, sparrows, finches and other seed-eating birds that make their homes on farmlands.
The researchers report in Proceedings of the Royal Society B that the use of broader-spectrum herbicides (chemicals that can kill just about everything except the food plant) on these crops can sharply reduce the amount of weed seeds, an important food source for the birds.
The researchers, from the Royal Society for the Protection of Birds and other groups, used data from studies that compared transgenic and conventional crops and analyzed the results for the diets of 17 bird species. They found that with transgenic beets and oilseed rape (canola is a variant of it), there was significantly less weed seed available to most of the species.
Perhaps surprisingly, though, with transgenic corn there was more seed available, though the amount was significant for only seven of the bird species. While the broad-spectrum herbicide used for corn kills more types of weeds, it doesn't do as good a job of killing them as the herbicides used with conventional corn.New York Times
