Fungi as Fixers

The plants in this restored prairie at Elm Creek Park Reserve are mostly mycorrhizal. Fungi live with their roots in a mutually beneficial relationship.

The last post introduced mycorrhizae, the fungus-root associations that benefit both partners. The fungus transports nutrients and water to the plant, while the plant gives sugars and other carbon-containing molecules to the fungus. Most plants are mycorrhizal and are dependent on this symbiosis for their best growth.

On a larger scale, mycorrhizae are also important in ecological restoration, the practice of regenerating native plant communities after they’ve been degraded or destroyed. They may also help with carbon sequestration, in this case the storage of carbon in fungal mycelia, the underground bodies of fungi.

Mycorrhizae and Ecological Restoration

In a 2023 review article, a team of scientists led by Lisa Markovchick wrote about a gap between the science and practice of using mycorrhizae in restoration projects. Although research supports such use, practice lags, in part because of negative views of fungi as only pathogens.

To counter this perception, Markovchick and her collaborators offer insights from research and tips for both protecting mycorrhizal fungi and deploying them during restoration projects. A few of those insights and tips are below. Links to Markovchick’s full paper and a webinar summarizing her work follow the list.

According to Markovchick and her collaborators:

• Mycorrhizae perform many functions, such as promoting water infiltration and retention, preventing erosion, and boosting plant nutrition, survival, and resilience.
• Mycorrhizal fungi also have roles in providing ecosystem services, such as responding to disturbance and providing habitat for other organisms, thereby enhancing biodiversity.
• Change in land use, drought, invasive plants, and other disturbances can deplete mycorrhizal fungi or change the fungal species present. Even some necessary practices, such as applying herbicides to invasive plants, can affect mycorrhizae.
• The benefits of mycorrhizal fungi are clear from many studies. For example, they can significantly increase species richness (the number of different plant species in a community), and plant biomass, and their effects tend to grow with time.
• There must be a good match between plants and mycorrhizal fungi when both are used to restore a community. Mass-produced mycorrhizal fungi may not provide that important pairing, leading to neutral or negative results. Introducing fungi from a native community near the restoration site has proven most beneficial.

References

The Gap Between Mycorrhizal Science and Application. Wild Earth Guardians YouTube video featuring Lisa Markovchick. 53:46.

The gap between mycorrhizal science and application: existence, origins, and relevance during the United Naton’s Decade on Ecosystem Restoration. Lisa M. Markovchick, Vanessa Carrasco-Denney, Jyotsna Sharma, and others. Restoration Ecology Vol. 31, No. 4. May 2023.

 

Mycorrhizae and Carbon Sequestration

Potential solutions to a warming climate include nature-based options such as protecting forests, grasslands and wetlands. Protecting and enhancing mycorrhizal growth could be another solution, because plants transfer carbon-containing compounds such as sugars to below-ground fungal bodies (mycelia) and the roots they support.

The carbon that builds those compounds comes from atmospheric carbon dioxide captured during photosynthesis, and it can be a significant amount. In a 2023 review article, Heidi-Jayne Hawkins and others estimate that, globally, about 13 gigatons of carbon dioxide equivalents are transferred to the mycelia of mycorrhizal fungi each year. That amounts to about 36 percent of the carbon dioxide emissions from fossil fuels in 2021.

Living mycelia can also promote long-term carbon storage by releasing sugars and acids from their hyphae (the fungal strands that constitute the mycelium). These compounds eventually lead to the formation of mineral-associated organic matter, or MAOM. In this type of soil organic matter, carbon compounds are bound to clay, silt, or other mineral particles in soils. MAOM is slower to decompose, in part because it’s protected inside mineral aggregates that are harder for decomposers to access.

Even after fungal mycelia die, they can support carbon storage. Their organic matter is added to the soil, where it can attract soil particles and form the enlarging aggregates that stabilize carbon as MAOM.

The authors emphasize that there is more to understand about the flow of carbon into and through mycorrhizae and its effects on carbon sequestration. Still, they consider mycorrhizal fungi “a major carbon pool.”

Reference

Mycorrhizal mycelium as a global carbon pool. Heidi-Jayne Hawkins, Rachael I.M. Cargill, Michael E. Van Nuland, and others. Current Biology, Volume 33, Issue 11. June 5, 2023.

How can we support mycorrhizal fungi?

 Lisa Markovchick’s article recommends several actions and tips to improve the diversity and function of mycorrhizae, specifically in natural areas. A few of them are below. For a full list, see the link above.

• Protect source populations of mycorrhizae. Native communities with little or no history of disturbance are refuges for these fungi.
• When restorations are planned, include steps for soil conservation.
• Choose mycorrhizal fungi that are appropriate for the plant species being restored. This could be accomplished by introducing the “full diversity” of fungi from nearby native communities like the one being regenerated.
• Plants and their mycorrhizal fungi won’t associate unless both are alive and come into direct contact. Timing and placement are important, as is the source of fungi. Commercial mycorrhizal products may be a poor choice.