A century ago, the Asian vine kudzu was introduced to the southeastern US where its deep roots were thought to be helpful for erosion control. Since then the invasive species has been swallowing landscapes and altering ecosystems, and now it appears that the horrible plant increases air pollution as well.
Like many other legumes, kudzu (Pueraria montana) develops symbiotic associations between its roots and bacteria in the soil. These bacteria transform atmospheric nitrogen into ammonium, a nutrient for the vine, and when that “fixed” nitrogen is released to the soil, it becomes available to other plants and microbes.
The fast-growing legume fixes atmospheric nitrogen at a really high rate and the resulting increases in nitrogen cycling has triggered a dramatic increase in nitric oxide emissions from soils, according to a new paper in PNAS. Nitric oxide is a key precursor to ozone, and while this usefully blocks the sun’s harmful rays when it’s high in the atmosphere, it is an air pollutant that damages lungs and prevents plants from absorbing carbon dioxide when it occurs at the surface.
“It turns out that the changes you can’t see in a kudzu invasion are just as dramatic as the ones you can,” says lead author Jonathan Hickman of the Earth Institute at Columbia University (news release).
This new study is the first to establish the link between a biological invasion and bad air quality. And kudzu currently commands three million hectares and is expanding its reach by about 50,000 hectares each year. “It’s an impressive and dramatic plant,” Hickman says (Discovery News).
Using a chemical transport model, the authors show that kudzu invasion can lead directly to an increase of high ozone days—up to 7 days each summer in some areas, or 35% increase compared to a scenario without kudzu.
“While documenting these impacts on soil chemistry and nitric oxide emissions is definitely important, we really wanted to see whether an invasive species could affect the atmosphere in a meaningful way,” says Hickman.
Kudzu is sometimes called the vine that ate the South. Hickman suggests a new appellation: ‘the vine that choked the South’.
Image by lowrevolution via Flickr