Plant scourge of the South adding more carbon dioxide to the atmosphere, aiding in its own spread

Clemson University researchers are nearly lost in the overwhelming cover of kudzu vines, which have spread over every surface, object and tree in the area. (Credit: Clemson University News)

Tuesday, July 15, 2014, 10:16 PM - If you've ever driven through the U.S. Southeast, you've probably seen kudzu, the so called 'vine that ate the south,' covering a great deal of the local landscape. While this 'noxious weed' has been a problem for decades, as it grows at a remarkable rate and chokes out native species, research has shown that it is also responsible for releasing more greenhouse gases into the atmosphere than the plant species it is replacing.

First introduced to North America from southeast Asia in the 1880s, kudzu was hailed as the solution to many problems. It served a purpose as an ornamental shade plant to start, but it's edible (being part of the pea family), it's been used as livestock feed, fertilizer and for erosion control on vulnerable slopes. However, ever since the '40s, it has been gaining a worse and worse reputation, first losing favour with the US Department of Agriculture, and then being listed as a weed, then a noxious weed and an invasive species. The biggest problem initially identified about the plant is the rate at which it grows - up to 30 centimetres a day in ideal conditions (warm and wet) and that can add up to about 30 metres of growth in a season. 

It quickly covers the ground, buildings, and anything else around, blanketing fields and even climbing up trees. Any plants unfortunate enough to be overgrown (including trees) are deprived of sunlight by the dense cover of kudzu leaves and they quickly die out. These vines now cover over 3 million hectares of land throughout the U.S., mostly in the southeastern states - Georgia, Alabama and Mississippi - but it has spread south into Florida, west to Texas and north as far as Ontario. There is even a 'colony' in the U.S. northwest, specifically in Oregon. 

While these growths have taken on epic proportions, that's not the only problem from kudzu. It's already been shown that kudzu causes more nitric oxide (which is also a byproduct of burning fossil fuels) to be released from soils, which has caused an increase in ground-level ozone levels during summertime heat. In addition, as the plants continue to spread northward, especially with climate change, they are actually increasing the amount of carbon dioxide released from the soil into the atmosphere, introducing a feedback loop. 

According to Malcolm Campbell, a professor and the vice-principal research at the University of Toronto, in his piece in The Conversation, the research of Nishanth Tharayil and Mioko Tamura, from Clemson University, shows that the plants choked out by the kudzu tend to lock more carbon into the soil. This is especially true in the case of pine forests. Pine needles are very resistant to being broken down by microbes, thus the carbon stored in the needles gets buried in the soil and locked away. Kudzu, on the other hand, has leaves that are broken down very easily, thus releasing their carbon just as easily. Not only that, but as these microbes (which were used to the rate at which the pine needles could be broken down) get a taste of the kudzu, it gets easier for them to break down other organic matter as well. So, the microbes can go after the buried organic matter as well, releasing that carbon along with what gets released directly from the kudzu litter. The study, published in New Phytologist, showed that despite a 22 per cent increase in soil litter (due to the abundant leaves the kudzu drops during winter), there was a 28 per cent decrease in soil carbon after a kudzu infestation invades an area.

According to a Clemson University press release, Tharayil said: "Our findings highlight the capacity of invasive plants to effect climate change by destabilizing the carbon pool in soil and shows that invasive plants can have profound influence on our understanding to manage land in a way that mitigates carbon emissions."

The press release goes on to say that, if this is happening across the entire 3 million hectares of land the kudzu currently covers, this invasive plant is releasing enough carbon from the soil each year to equal what is sequestered by close to 5 million hectares of U.S. forest.

"Climate change is causing massive range expansion of many exotic and invasive plant species. As the climate warms, kudzu will continue to invade northern ecosystems, and its impact on carbon emissions will grow," Tharayil said in the press release.

There is a solution to this particular problem from kudzu, according to the research. Since kudzu performs better than other plants in soils with low nitrogen content, introducing more plants that will increase the amount of nitrogen in the soil - "beans, peas, soybeans, peanuts and lentils," says Tharayil - will give other plants a better chance of surviving and giving kudzu less of a chance of taking over.

As for dealing with the current infestations of the vines, many solutions have been tried, with varying costs and degrees of success. Despite the monumental task, though, it is probably worth the effort to prevent kudzu from spreading any further.

(Teaser image courtesy: Scott Ehardt, via Wikipedia)

(Update: Through corresponding with N. Tharayil, the carbon values reported by Clemson University's The Newstand have been updated, and these updates are reflected above.)