Kudzu Causes Global Warming!
Across the southeastern US, the nitrogen-fixing legume Pueraria montana, more commonly known as kudzu, has been an impossible to eradicate invader for decades. While its direct impact on native ecosystems is highly visible—a smothering green blanket that swallows up shrubs, trees and even houses—what is not as apparent is kudzu's effect on the atmosphere. Its spread has the potential to raise ozone levels by increasing nitric oxide (NO) emissions from soils by as much as 100%. Since NO is a potent greenhouse gas, the spread of the pesky vine could be a contributing factor to climate change. That's right: kudzu causes global warming!
Kudzu, a member of the pea family, is a climbing, coiling, and trailing vine native to southern Japan and southeast China. Introduced from Japan into the United States in 1876 at the Philadelphia Centennial Exposition, it was promoted as a forage crop and an ornamental plant. The green invader is certainly not all bad. It increases nitrogen in the soil via a symbiotic relationship with nitrogen-fixing bacteria and its deep taproots can transfer valuable minerals from the subsoil to the topsoil. Kudzu can be used as high quality forage for grazing animals. From 1935 to the early 1950s, the Soil Conservation Service encouraged farmers in the southeastern United States to plant kudzu to reduce soil erosion.
Hot, humid summers, frequent rainfall, and temperate winters with few hard freezes make the southeastern US a perfect haven for kudzu. With no natural predators things were soon out of control, with the fast growing leafy vine seemingly covering everything in sight. This rapid growth soon earned it such nicknames as the “foot-a-night vine” and “the vine that ate the South.” Over a period of several years, Kudzu will kill trees by blocking the sunlight. For this and other reasons many would like to find ways to get rid of it. Kudzu was named a pest weed by the United States Department of Agriculture in 1953.
Abandoned houses in Georgia taken over by kudzu. Photo: Jack Anthony.
Now comes news, published in the Proceedings of the National Academy of Science (PNAS), that kudzu may also be contributing to global warming. In their paper “Kudzu (Pueraria montana) invasion doubles emissions of nitric oxide and increases ozone pollution,” Jonathan E. Hickman et al. have identified kudzu as a major contributor to GHG emissions. How the ubiquitous green vine does this is a mater of soil biology:
When symbiotically fixed nitrogen is released to the soil from decomposing tissues or leaked from roots, it becomes available to other plants and microbes. Because of these additions of fixed nitrogen to soils, invasions by N-ﬁxing plants tend to cause the overall rate of microbially mediated N transformations in the invaded ecosystem to increase, including rates of nitrification [the oxidation of NH4+ to nitrate (NO3-)] and denitrification (the reduction of NO3- to N2). When rates of these N transformations increase, gaseous emissions of NO and the powerful greenhouse gas nitrous oxide (N2O), which are by-products of nitrification and denitrification, tend to increase as well.
I have previously commented on nitric oxide and nitrogen dioxide (NO and NO2), generically referred to as nitrogen oxides (NOx), both potent destroyers of stratospheric ozone that derive primarily from surface nitrous oxide (N2O) emissions. Nitrous oxide (N2O), also known as laughing gas, is emitted from soil fertilization, livestock manure, sewage treatment, combustion and some industrial processes, but NO from kudzu is a new twist.
According to the paper, an observed doubling of NO emissions due to kudzu in Georgia suggests that the ongoing kudzu invasion could increase regional ozone concentrations as the plant continues to spread throughout its current range. The increase in NO emissions from soils invaded by kudzu occurs against a background of decreasing NO emissions nationally. Between 1990 and 2007, NOx emissions in the United States decreased by 33% , primarily due to reductions in emissions from highway vehicles and stationary fuel combustion.
Kudzu has spread across the southeastern US.
In the researchers' most extreme scenario, kudzu produces a 28% increase in soil NO emissions and a subsequent spike in ozone concentrations, relative to the scenario in which kudzu is not included. The areas most vulnerable to the increase in NO fluxes were parts of Mississippi, Arkansas, and Tennessee. In these areas, the frequency of high ozone episodes—defined as the number of days for which the daily maximum 8-h ozone levels exceed 70 ppb—increases by up to 7 days during the 3-month period. Instead of worrying about AGW, anthropogenic global warming, we should be concerned about KGW, kudzu global warming.
Steps to eradicate the plant pest have been taken by the Agricultural Research service (ARS). It is estimated that kudzu spreads at the rate of 150,000 acres annually, easily outpacing the use of herbicide spraying and mowing, as well increasing the costs of these controls by $6 million annually. The city of Chattanooga, Tennessee has undertaken a trial program using goats and llamas that graze on the plant. As of 2007 the goats are grazing along the Missionary Ridge area in the east of the city. Even so, Kudzu is well established and is nothing if not tenacious.
Some have even suggested turning kudzu into bioethanol, though the economics of doing so are questionable. The roots are by far the largest source of carbohydrate in the plant—up to 68 percent carbohydrate by dry weight. By comparison, the leaves and vines only contain a few percent. Researchers estimate that kudzu could produce 2.2 to 5.3 tons of carbohydrate per acre in much of the South, or about 270 gallons per acre of ethanol, which is comparable to the yield for corn of 210 to 320 gallons per acre.
Unfortunately, kudzu roots grow deep, often more than six feet and often in hard to access places. According to a report published in Biomass and Bioenergy, about one-third of kudzu plants would be harvestable. If so, they calculate that harvesting kudzu could produce only about 8% of the 2006 US bioethanol supply, around 480 million US gallons per year. That sounds like a lot, but compared to the EIA estimated US gasoline consumption of 378 million gallons per day it is a rather paltry amount.
It would seem that, even though NOx emissions have dropped in the US, nature is doing some GHG emitting of its own to compensate. The IPCC may find some solace in the fact that people were responsible for transplanting kudzu, and hence causing increased emission of greenhouse gases. This indirectly puts the blame for global warming back on humanity's shoulders, at least by warmist reckoning. But then, according to the climate change alarmists everything humans do harms the environment. I have a suggestion for all those climate change true believers out there: instead of blaming humanity for global warming, go uproot some kudzu and really fight climate change.
Be safe, enjoy the interglacial and stay skeptical.