Can soil microbes save us from global warming?

Soil carbon storage is critical to life on Earth, as it contains more carbon than the atmosphere and plants combined. However, the increasing frequency and severity of droughts threaten to disrupt this ecosystem, since soil microbes are primarily responsible for storing carbon.

Steven Allison, a microbial ecologist at the University of California at Irvine, warns in an opinion piece in 'Trends in Microbiology that adapting soil microbes to drought at a faster rate than that of plants could affect the health of the soil and future levels of greenhouse gases.

Allison emphasizes the importance of understanding how microbes respond to drought in order to manage the future situation in agricultural and natural settings. Soil microbes participate in the carbon cycle and play a role in carbon removal and fixation, as well as its release into the atmosphere. It is crucial that all three groups continue to do so to maintain the balance of the ecosystem.

Allison stresses that the impact of climate change and drought on soil microbes should not be overlooked, as they are vital to carbon and nutrient cycling.

"Carbon 'sequestered' in the soil has knock-on effects to the rest of the world in terms of infrastructure in our natural and managed ecosystems," Allison says. Viewed another way, microbes could be vital in tackling global warming because the accumulation of carbon in the soil depends on them.

Very long droughts

A high-carbon soil is essential for plant productivity due to its abundance of nutrients and physical properties that prevent erosion. However, global warming is causing prolonged droughts and heavy rains, which release carbon from the soil and contribute to erosion, landslides and sediment transport.

To mitigate the effects of the climate emergency, it is important to increase carbon in plants and soil and reduce it in the atmosphere. Therefore, it is crucial to understand how the balance between incoming and outgoing carbon changes with different climatic factors, such as droughts and rising temperatures.

Allison cautions that microbes can adapt faster than plants to these changes, potentially upsetting the delicate balance of carbon storage in the soil. Microbes can evolve rapidly, changing their physiology and abundance to adapt to drought, while plants can have a hard time keeping up.

Carbon poor soils

The implication of all this is that if more carbon-releasing microbes survive than carbon-sequestering microbes, it could lead to carbon-depleted soils, which would have serious negative implications for plant productivity and future levels of greenhouse gases, Allison said.

"Right now, we have data that suggests that when there is drought, something changes that results in carbon loss, but we don't understand exactly how or why that happens if the drought is changing the abundance of beneficial microbes associated with plants versus carbon-releasing microbes, or whether it's driving the evolution of one of the groups of microbes, or whether it's more determined by changes in their immediate physiology," he added.

Allison sees it as possible "to push the balance in the right direction", but qualifies that for this there is "much to be done", and "more research" is needed.

Some microbes could help plants cope with drought. If you can figure out which microbes are most beneficial to plants and most likely to sequester carbon in the soil, you could try to tip the scales in your favour.

"There's a lot of potential for us to manage or engineer soil microbes," Allison says. "In agricultural systems, we can manipulate the soil or add microbes that remove carbon," he adds.

"In more natural systems, management should probably focus on plants: soil microbes are often closely intertwined with plants, so plant management can also benefit the microbial part of the ecosystem," says the ecologist.

Among his proposals, to investigate how drought affects the presence of carbon in the soils of different habitats, "from the arctic tundra to the deserts," he concludes.

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