Several studies show that biochar can benefit soil. Now, new research shows one crucial way it appears to do that: by supporting ants which were found to build stronger, more complex colonies in the presence of this soil improver. But as the new study shows, there’s also a trade-off: too much biochar, and ants go into a decline.
This is the first study to examine the effects of biochar on “large soil fauna” like these, looking beyond just microbes and agricultural yields, the researchers say. They went in with a hunch that the enriching substance would influence ant behaviour in some way, and to test it out they designed a series of experiments.
First, starting with biochar made of pyrolized rice straw, they mixed varying amounts—2.5%. 5% and 10%—into samples of soil. These they compared with a soil sample that didn’t contain any biochar. To each of the four soil experiments, they added 30 worker ants from a common local species. Then, they watched and waited.
Of particular interest was how the ants nested, socialized, and foraged in each of the soil experiments. The first thing the researchers recorded was a sharp difference in survival rates: over 83% of the ants survived when they were exposed to no biochar, or to limited amounts ranging from 2.5% to 5%. Meanwhile at 10%, their survival declined precipitously, to about 55%.
The ants were also more productive with biochar, but at lower doses. At levels of 2.5%, they developed larger and more complex nest sites, in fact almost threefold more complex than in experiments containing 10%. Ants also foraged with double the efficiency in samples with 5% biochar compared to higher dosing, travelling more quickly through the soil, showing the most success at securing food, and also finding it more quickly. As well as this, at more moderate doses of biochar ants displayed stronger social cohesion, yet were more aggressive towards invasive species and protective of their colonies, compared to ants in soils containing no biochar.
The researchers think these interesting behavioural differences come down to biochar’s variable effects on soil chemistry. At low doses biochar slightly raises pH, which improves moisture retention in the soil and might make conditions more appealing to nest-building ants. However in larger quantities the pH can rise to levels that threaten ants’ internal balance and so become toxic to them. And because ants use elements of the soil to communicate, even small shifts in its chemistry and microbial makeup brought about by biochar can change the way they interact with one another, sharpening or dimming their communication.
The reason any of this matters is because ants are major architects of quality soil. Socially-bonded and efficient foragers that make large, complex nests will improve soil structure and function, distribute nutrients through the terrain, and improve drainage, among other things.
The authors’ main takeaway? Biochar may be more important to the wider health of the ecosystem than we realized—and that means thinking more carefully through precisely how it’s used. “Too much can disrupt the very biological systems we aim to restore,” the authors say.
Liu et. al. “Biochar application enhances ant (Formica japonica) ecological functions as indicated by their social behaviors.” Biochar. 2026.
Image: ©Anthropocene Magazine
