13 September 2016

Fungi make steep slopes more stable

Posted by bbane

By Brendan Bane

White mycorrhizal fungi grow entangle the brown roots of a white spruce. Credit: Silk666.

White mycorrhizal fungus entangles the brown roots of a white spruce. Credit: Silk666.

Fungi are fantastic. They give us beer, bread and cheese. And if those delicious reasons aren’t sufficient, then here’s another: a new study suggests some fungi can help prevent shallow landslides and surface erosion.

The new study, published in the Journal of Geophysical Research: Biogeosciences, a journal of the American Geophysical Union, tested mycorrhizal fungi’s ability to make steep and gravely slopes more stable and less prone to shallow landslides.

Like clown fish and anemones, mycorrhizal fungi and plants share a symbiotic, or mutually beneficial, relationship. Mycorrhizal fungi grow around and sometimes inside a plant’s roots. Plants provide fungi with fuel. In return, fungi grow into the surrounding soil and fetch nutrients like phosphorous and nitrogen for the plant.

Plants with mycorrhizal fungi usually grow faster and live longer than plants without the fungi. Fungi can even protect plants from pathogens.

“It’s quite a simple circle,” said Alexander Bast, a geoscientist at the Swiss Federal Institute for Forest, Snow, and Landscape Research, and lead author of the new study. “The plant gives something and the fungi give something.”

The study’s authors suspected mycorrhizal fungi could stabilize soil by strengthening plant root systems. Several studies had demonstrated the stabilization effect in the lab, but no one had done so on steep, alpine slopes, according to Bast.

To test the effect, the study’s authors planted several hundred plants in the slopes of the eastern Swiss Alps and inoculated them with a commercial fungi. The area has many coarse-grained slopes composed of large, loose soil particles that are prone to failure and erosion. A changing climate brings greater chances of torrential rain, according to the study, and that rain could bring more shallow landslides.

The researchers monitored the fungi’s influence on soil stability and plant growth over three years. They inoculated some areas of a slope with fungi, leaving others untouched as controls. They periodically removed soil cores and assessed the size and shape of the roots growing inside them. By submerging the cores underwater and measuring how much material was shed, the researchers were also able to assess the soil’s cohesiveness, or stability.

Surprisingly, the soil without fungi was more stable than soil with fungi during the first year, according to the study. Just as a plant’s stalks grow toward sunlight, its roots stretch outward to find water and nutrients. But if those nutrients are provided early on by mycorrhizal fungi, the roots have no incentive to grow outward and instead grow thicker. The plants without fungi grew roots that were thinner and more outstretched than the plants with fungi, leading initially to greater stability of the soil.

But, over time, the fungus-aided plants grew roots that were much thicker than the non-fungi plants. Also, more plants survived in areas treated with fungi than those without fungi.

The combination of thicker roots and greater number of surviving plants eventually boosted the fungus-treated soil’s structural integrity. After three years, fungi-slopes became significantly more stable than non-fungi slopes, according to the study. Strengthened soil makes shallow landslides less likely, said Bast, and stronger plants also help prevent surface erosion.

The new study shows fungi could be used to stabilize landslide-prone slopes, he said, adding that he would encourage landowners to inoculate their slopes with fungi as a preventative measure.

Bast said the same technique could be applied to areas outside the Swiss Alps. He encouraged those who wish to experiment with the stabilization effect to, when inoculating their slopes with mycorrhizal fungi, crosshatch their plots. That way they may enjoy both the initial stability of non-inoculated plants and the long-term stability of fungi-aided plants.

Bast said he would like to explore fungi’s influence on root development on a cellular level, which could explain if mycorrhizal fungi help roots resist breakage. In general, many mysteries, like the molecular details of nutrient exchange between roots and fungi, or the number of mycorrhizal fungi species, still remain. By exploring the relationship between roots and fungi further, eco-engineers could better harness the power of fungi to prevent landslides, Bast said.

-Brendan Bane is a science-writing intern in AGU’s Public Information department.