Copied from The Conversation News Letter
A formidable ally in the fight against climate change is hidden under our feet. New research suggests 36% of the carbon dioxide (CO₂) emitted from burning fossil fuels each year is taken up by a group of fungi called mycorrhizae, which live in partnership with plants in the soil.
All you’re likely to see of these organisms is a mushroom protruding from the earth. But underground, mycorrhizal fungi form threads called filaments that connect the roots of most plants, exchanging water and nutrients for sugars and fats made by photosynthesis.
The academics behind the new research believe scientists have massively underestimated the role fungi play in keeping the man-made gases driving climate change out of the atmosphere. And these fungi are in good company: countless species are active participants in the carbon cycle, and they need our help to ensure they can continue helping us.
You’re reading the Imagine newsletter – a weekly synthesis of academic insight on solutions to climate change, brought to you by The Conversation. I’m Jack Marley, energy and environment editor. This week, we meet the species working hard to slow global heating.
“On land, the natural carbon cycle involves a delicate balance. Plants take CO₂ from the atmosphere through photosynthesis, while other organisms emit it back into the atmosphere,” say Adam Frew, Carlos Aguilar-Trigueros, Jeff Powell and Natascha Weinberger, who study how plants and soil microorganisms interact at Western Sydney University.
“Now we know the carbon transfer from plants to mycorrhizal fungi isn’t a side note – it’s a substantial part of this equation.”
Animals release some CO₂ when they exhale. But they can also help bury carbon – and increase its duration in safe storage underground.
While most of the carbon stored in trees is decomposed and recycled to the atmosphere as greenhouse gas in less than a century, the soil beneath grasslands with few trees but lots of large plant-eaters, such as elephants, can guard carbon for thousands – even tens of thousands – of years in hard-to-reach underground pools.
So how do these animals do it? Jeppe Aagaard Kristensen, a visiting postdoctoral fellow at the University of Oxford’s Ecosystems Lab, says that up to half of the plant matter eaten by elephants is excreted as dung or urine. Decomposers like beetles and earthworms can break this down more easily than dead leaves, for instance, since it’s already been digested, and the carbon contained within it then enters long-term storage in the soil.
“Large animals seem adept at reorganising where ecosystems store carbon, directing a larger fraction towards persistent and stable reservoirs underground,” says Kristensen.
“This shows how valuable intact wildlife communities can be, and should urge us to protect the few remaining herbivore-rich ecosystems on Earth, such as the African savanna.”
And it’s not just herbivores: a recent study showed how a 50-year campaign to restore tiger populations in India had unexpected benefits for the climate.
Project Tiger established nine tiger reserves in 1973. Today, 54 such areas exist across India – that’s 75,000 sq kilometres of jungle, mangrove swamp and dry forest which equates to 2% of the country.
“These habitats might seem very different, but the common link is of course lots of trees,” says Simon Evans, a principal lecturer in ecotourism at Anglia Ruskin University.
The strict protection afforded to tigers within this network of reserves prevented deforestation – and may have kept 1 million tonnes of CO₂ out of the atmosphere as a result between 2007 and 2020.
Some species, such as the African forest elephant, can even increase the capacity of forests to store carbon. A typical three-tonne female must eat roughly 200kg of bark and leaves daily. Saplings are particularly popular as they have fewer of the chemical defences which make older trees in a tropical forest difficult or unpleasant to eat. By weeding out the small, fast-growing vegetation, elephants promote larger, woodier trees which lock up more carbon.
“The authors estimate that the disappearance of African forest elephants would result in a loss of as much as 7% of the carbon stocks in Central African forests”, Evans says.
It’s important to not get carried away, however. You may have heard that whales are good at drawing carbon down from the air and into the deep sea, for example.
“Their plumes of poo contain so many nutrients that phytoplankton blooms can form in a whale’s wake. These tiny photosynthesising creatures soak up carbon dioxide in their bodies. When they die, they can sink to the bottom and be covered in sediment, storing the carbon,” explains Olaf Meynecke, a research fellow in marine science at Griffith University.
However, Meynecke’s research suggests that whales are likely to only make a limited contribution to carbon storage. Of the 53 billion tonnes of carbon absorbed by the oceans annually (mainly as a result of photosynthesising algae), 4 billion tonnes sink below the surface and only 1% of that is stored in sea-floor sediment for the long term.
Not enough is known about the climate benefits of whale conservation. Trumpeting its usefulness could distract from proven solutions such as preventing the burning of fossil fuels, Meynecke says.
Even so, understanding how large wild animals in particular mitigate climate change exposes important connections between the multiple aspects of the ecological crisis, according to Heather Alberro, a lecturer in global sustainable development at Nottingham Trent University.
Alberro highlights how the captive rearing of animals for meat and dairy is one of the largest contributors to climate change. In contrast, animals that are allowed to embed themselves in natural cycles can help return carbon to long-term storage.
“Robin Wall Kimmerer, environmental scientist and citizen of the Potawatomi Nation, refers to the ‘honourable harvest’. When deciding anything — from how and where to build homes to how to produce food and source energy — principles to live by include taking only what we need, always leaving some for others, and sustaining those who sustain us.”