Rachel Williamson
Rachel Williamson is a business and science journalist based in Melbourne.
Doctors do poo transplants to rebuild broken gut microbiomes, so why not soil transplants to rebuild underground communities damaged by drought or overuse?
But given how little we know about the world under our feet – one said to contain 59% of all life on earth – what soil scientists hope could work to conserve and preserve soils and flora in a hotter, drier future world rubs against what has been found to work today.
The theory is this: soil microbiomes adapt to the climatic conditions they live under and influence how well the flora above tolerate those same conditions. In Australia, the dominant bacteria in the soil is the drought-tolerant actinobacteria – a detail uncovered by researchers mining the Bioplatforms Australia’s soil data. So in native bushlands where the soil is clearly adapted to dry conditions, why not harvest some of those microbial communities for drought-struck farmland? Or from rainforests to restore ex-grazing land?
“We’re doing some tinkering here in trying to do that for native plant species in particular. So if you shift soils around the landscape… if you bring those soils down south, do you get greater drought resilience of local plants down here? That might be an extremely useful tool when we talk about climate adapted restoration plantings,” says Martin Breed at Flinders University, a specialist in ecology restoration and one of Australia’s top soil researchers.
“There’s going to be genetic limits for plants and how they can adapt to climate change. There’s other things that can also help facilitate plants adapt to climate change, and that’s things like the microbial communities they associate with.”
Soil doesn’t recover easily
Worldwide, ecosystem degradation has become so bad that in 2021 the UN declared the 2020s the Decade on Ecosystem restoration. Yet this is a difficult, unpredictable process with low success rates.
A surprising study in 2004 shows just how difficult soil restoration is.
Ecosystem degradation has become so bad that in 2021 the UN declared the 2020s the Decade on Ecosystem restoration.
A site in Northeast Queensland was deforested about 70 years ago and used for unfertilized pasture for 30 years. It was abandoned and in 1994 planting with native rainforest flora began.
In 2000, soil tests found that concentrations of organic carbon, nitrates, and other critical nutrients were significantly lower than in the untouched rainforest nearby, and the soil was still more acidic.
“Though we did not anticipate the soil under the abandoned pasture to recover 100% in 30-40 years, the results indicate that… 30 years of abandoned pasture plus 10 years under recently planted rainforest was not sufficient to bring about substantial improvement in soil properties comparable to the rainforest,” the study said.
“This implies the resiliency of tropical soils, in general, to recover from deforestation and cultivation induced degradation is poor.”
Which is why researchers are reaching for new ideas, like soil translocation.
Life underground
Underground communities are made up of a range of species and home to 3% of all mammals, half of all bacteria on earth, 86% of plants and 90% of fungi, according to the study which bumped up the biological quota of soil in August to 59%.
Plants and soil are in a symbiotic relationship, says Flinders University plant researcher Dr Sunita Ramesh.
“[Plants] get help from the bacteria [and fungi] which provide certain nutrients… Mycorrhizal associations with the roots of the plant gather nutrients such as phosphate,” she told Cosmos.
Plants and soil are in a symbiotic relationship.
Dr Sunita Ramesh
“And plants actually exude from their root tips… carbon and nitrogen. Sometimes even organic acids come out. And all of this actually helps attract these beneficial microbes.”
Add some water and the microbiome changes, as fungi and hydrophilic bacteria thrive. Make the air hotter and drier, and other species in the microbiome will come to the fore. In both instances the texture of the soil – the way it clumps together – changes as well.
And it is because of this intense link between the above and below ground worlds, and the way soil microbiomes react to changing climate, that is leading ecologists to focus some of their efforts underground.
It… kind of works…
Earlier this year, a Dutch review study unveiled its big conclusion about translocating soil for restoration efforts: it’s complicated.
The study took data from 46 field experiments that took place in 17 countries across four continents.
Translocating soil, either as an intact turf, broken up into “spreadable crumbs”, or as a soil slurry, allowed restoration sites to regrow faster, but worked best in loamy soils and on a larger scale. But a larger scale also means devastating a donor site.
Translocating soil for restoration efforts: it’s complicated.
“There are strong indications that restoration of target plant communities can take decades to centuries,” wrote lead authors Gijs Gerrits and Rik Waenink.
“When the goal is to restore functionality (i.e. restoring vegetation cover) and large volumes of donor material would be needed, sacrificing well-developed donor vegetation is probably not a worthwhile strategy.
“However, when one is trying to rescue rare habitats from extinction and the objective is to recreate intact phytosociological plant communities then the effort and cost that comes with turfing might well be justified.”
The spanner in the works
One of the experiments that complicated the review’s results was one that took place at the end of the Millennium Drought in Victoria.
Botanist Tim Wills, who runs a consultancy called The Ecology Office, was an author on the review because he was involved in the Victoria study which trialled translocating slabs of earth during the construction of the 70 kilometre, just-in-case-of-drought North–South Pipeline.
They hoped that moving whole slabs of soil containing endangered Golden Sun Moth larvae would allow the species to recover more easily than after using the usual process of stripping the topsoil and putting it back afterwards.
“We wanted to use the construction of this pipeline as an opportunity to trial a few different restoration techniques to see what would work best in terms of rehabilitating the pipeline easement after construction, so the grassland would come back as natural as possible and hopefully it would be useful habitat for the Golden Sun Moth,” Wills told Cosmos.
“What we did on this study, which was out near Yay, was trial a number of techniques. One of them was spreading topsoil, the other major one was using heavy machinery to pick up slabs of habitat 1m by 1m, and about half a metre deep. We trialled a few different depths of soil to see if that made a difference.”
As far as Wills knows, this was the first time this experiment had been conducted in Australia.
“What we found was it was an incredibly labour intensive method, a very costly method… and we found there were a number of problems with the methods. Maybe that was unique to the soil and environment we were working in [during the end of the Millennium Drought]. It was very crumbly, it was very hard to keep intact.”
“You would have been better off scraping the topsoil and re-spreading it back.”
Soil translocation is a work-in-progress for Australian habitats.
Since the Golden Sun Moth experiment, new thinking around soil restoration has gone the other way: scrape off the topsoil entirely.
Native grasslands are critically endangered ecosystems in Australia, with estimates of just 0.1% remaining from pre-European times.
Multiple experiments on Victoria’s Volcanic Plains, which stretch from Melbourne to the South Australian border, and in New South Wales showed that soil scalping removed exotic seeds and overly nutrient rich loam, which allowed native grasses which prefer poorer earth to get a head start.
Soil translocation is a work-in-progress for Australian habitats, but as predictions of higher temperatures and changed weather patterns become more confident – and extreme – endangered flora and habitats will need all the help they can get.