Is Japanese knotweed SPEEDING UP global warming? Invasive species could be increasing CO2 levels in the atmosphere

Researchers in South Carolina say invading species are releasing carbon



The scientists found both kudzu and knotweed unbalanced ecosystems



This caused them to release carbon that had been stored in the soil



U.S. kudzu invasion alone is comparable to 540 millions gallons of gasoline



And they say the effect on agricultural land management could be dramatic



We all know plants absorb carbon dioxide and expel oxygen, giving us the safe and clean air that humans breathe.

But now scientists have said that some invasive species of plant such as Japanese knotweed and kudzu can unbalance an ecosystem and release carbon stored in soil into the atmosphere.

The researchers at Clemson University in South Carolina estimate that, in a year, the invasion of kudzu in the U.S. alone can unleash the equivalent amount of carbon from 540 million gallons (2.5 billion litres) of gasoline.



A study suggests that invasive plant species such as Japanese knotweed (pictured) could be unleashing a significant amount of carbon into the atmosphere, because it causes the ecosystem it inhabits to become unbalanced and releases carbon that was previously stored in the ground

The scientists examined how invasion by exotic plant species can affect the ability of soil to store greenhouse gases.

WHAT IS KNOTWEED?

Japanese knotweed - which has the scientific name fallopia japonica - was introduced into Britain by the Victorians.

Incredibly invasive, it can grow four inches (ten centimetres) in a day from April to October and a tiny root can establish itself as a plant in just ten days.

Apparently solid structures such as tarmac and flooring in houses are no barrier to its growth and the weed also creates a risk of flooding if leaves clog waterways.

Knotweed is recognised by its shovel-shaped leaves, bamboo-like stem and white flowers produced in autumn.



The research could have far-reaching implications for how people manage agricultural land and native ecosystems.



In a paper published in the scientific journal New Phytologist, plant ecologist Nishanth Tharayil and graduate student Mioko Tamura show that invasive plants can accelerate the greenhouse effect by releasing carbon stored in soil into the atmosphere.

Since soil stores more carbon than both the atmosphere and terrestrial vegetation combined, the repercussions for how agricultural land and ecosystems are managed to store carbon could be dramatic.



In their study, Tamura and Tharayil examined the impact of encroachment of Japanese knotweed and kudzu on the soil carbon storage in native ecosystems.



They found that the invasion of kudzu released carbon that was stored in native soils, while the carbon amassed in soils invaded by knotweed is more prone to oxidation and is subsequently lost to the atmosphere.



'Our findings highlight the capacity of invasive plants to effect climate change by destabilising 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,' Tharayil said.



Tharayil estimates that kudzu invasion results in the release of 4.8 metric tons of carbon annually, equal to the amount of carbon stored in 11.8 million acres of U.S. forest.



This is the same amount of carbon emitted annually by consuming 540 million gallons (2.5 billion litres) of gasoline or burning 5.1 billion pounds (2.3 billion kilograms) of coal.

The researchers found that the invasion of kudzu (picture) released carbon that was stored in native soils, while the carbon amassed in soils invaded by knotweed was more prone to oxidation and is subsequently lost to the atmosphere. The kudzu invasion in the U.S. results in the release of 4.8 metric tons of carbon annually

'Climate change is causing massive range expansion of many exotic and invasive plant species,' said Tharayil.



'As the climate warms, kudzu will continue to invade northern ecosystems, and its impact on carbon emissions will grow.'



The findings provide particular insight into agricultural land-management strategies and suggest that it is the chemistry of plant biomass added to soil rather than the total amount of biomass that has the greatest influence on the ability of soil to harbour stable carbon.

But the researchers point out there is a way to mitigate the effects.



'Our study indicates that incorporating legumes such as beans, peas, soybeans, peanuts and lentils that have a higher proportion of nitrogen in its biomass can accelerate the storage of carbon in soils,' Tharayil said.

