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Soil microbe transplant could improve tree growth and remove more CO2

A site in Wales that is part of the tree-planting scheme run by The Carbon Community

The Carbon Community/Paul Box

The soil equivalent of a faecal microbiome transplant and the effect of sprinkling rock dust are to both be tested at scale in tree-planting schemes to see if they can turbocharge the amount of CO2 removed from the atmosphere.

In the past few weeks, UK charity The Carbon Community has planted 25,000 trees across 11.5 hectares of former farmland in Carmarthenshire, Wales. This forest will host a trailblazing experiment to see if and how the two approaches can accelerate carbon sequestration.

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The first involved taking soil microbes and mycorrhizal fungi from a nearby established forest and using them to kickstart the saplings’ growth, which has the potential to increase the amount of carbon that will be locked up in the trees’ stems and the soil.

The second experiment is intended to speed up the natural rate at which rocks absorb carbon from the air, by taking basalt rock dust from a quarry around 30 kilometres away and adding it to soil during the planting, a process known as enhanced weathering.

Both measures will be applied to native broadleaf trees, including birch and oak, and to a conifer used for timber called the Sitka spruce.

The results could help inform reforestation projects globally including those led by the UK government, which needs to plant at least 30,000 hectares a year to meet its 2050 net zero target. Such nature-based solutions are seen as a vital tool for tackling climate change.

“Natural tree regeneration will take a very long time on sites like this,” says Charles Nicholls at The Carbon Community, referring to the degraded nature of the soil on the former agricultural land. “If you look at both basalt and the microbiome injection, these are both natural processes that would happen anyway, but take decades. We are just trying to accelerate these natural processes.”

Past research paints a mixed picture of their potential, says Colin Averill at ETH Zurich, Switzerland, who is one of the project’s partners. Some studies show that manipulating the mycorrhizal communities in forests can increase tree growth and carbon removal by as much as 50-60 per cent but many other studies show no effect, he says. Averill is optimistic about the potential for a positive effect at the Welsh site, given the depleted nature of the soil there.

The first signs of the project’s success or failure will be whether it outperforms average tree survival rates, which can be as high as 40 per cent in tree-planting schemes. That will be followed by data on carbon sequestration in around two years. Most of the trees will take 35 years to reach maturity, with the site’s oaks taking longer still.

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