The Vine that Ate the South

Take a drive through parts of the southern US and you'll notice a bright green, ivy-like plant forming tents over many trees and telephone poles. It drapes itself from any possible hold, leaves vying for every ray of sunlight. In small bits it can be beautiful, but at the rate it's taking over the South it's downright scary.

The Kudzu vine (Pueraria montana) is an invasive species, originally from Asia, that was introduced to the southern US in the 1870s. In the mid 1900s, farmers and the Civilian Conservation Corps were encouraged to plant the vine wherever there was bare soil in an effort to reduce erosion. Unfortunately, like many introduced species (think starlings and zebra mussels) the kudzu vine was able to adapt to its new environment very quickly, sending out runners to establish new plants. (Click here to learn more about adaptation.) The result was that the vine began to quickly smother native species -- they can grow as much as 60 feet in one season, one foot per day!

New research published in PNAS shows that the kudzu not only chokes out other plants, but it's starting to choke out humans, as well. Like other legumes, kudzu and nitrogen-fixing bacteria in soil form symbiotic relationships. The bacteria help the plant to grow by producing ammonium; the plant gives the bacteria a nice, safe place to live. As the new research shows, however, the rate at which nitrogen is being fixed is problematic.

The journal Science explains: "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."

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Click here for more information on nitrogen cycling.

Image by lowresolution via Flickr