Fungus-rich soil can improve the durability of green roofs

Green roofs have become increasingly popular thanks to their benefits related to climate adaptation, mitigation and urban biodiversity management.

These green areas on building roofs absorb excess rainwater, reduce energy consumption by insulating buildings and cool neighborhoods, thus mitigating urban heat islands, while creating urban habitats for plants, pollinators and wildlife.

But in the United States, green roofs are typically planted with non-native plants in infertile soils, and their effectiveness diminishes over time.

A Dartmouth-led research team sought to determine whether managing green roof soil microbes could promote the healthy development of urban soils, a methodology that could be applied to support climate resilience in cities.

The team created an experimental green roof in Chicago to test how improving soil with native prairie microbes would change the soil microbial community over time. They were particularly interested in monitoring the presence of beneficial mycorrhizal fungi.

Mycorrhizal fungi are well known for living in roots and supporting plants in a symbiotic underground relationship, providing them with nutrients and water in exchange for plant sugars. Mycorrhizal fungi could be particularly useful to green roof plants that must withstand high temperatures, intense sun and periodic flooding.

Researchers added soil rich in native mycorrhizal fungi from a local restored meadow to the experimental green roof soil, called an “inoculum.” They planted inoculated, untreated soil with native prairie plants and green roof succulents.

For two years, the team tracked changes in the green roof’s mycorrhizal fungal community. They also compared the identified green roof fungal species to those present in the inoculum and in the air.

Their results demonstrate that active management of green roof mycorrhizal fungi accelerates soil development more quickly than if mycorrhizal fungal communities were to passively re-establish on their own. Green roofs treated with mycorrhizal fungi promote a more diverse soil community that is more likely to support the long-term sustainability of green roofs, according to results published in New phytologist.

“In this urban rooftop setting, we saw greater diversity in the fungal communities of the inoculated soil,” said lead author Paul Metzler, director of the Soil Ecology Laboratory in Dartmouth’s Department of Environmental Studies. “The long-term and consistent effects of the inoculum were quite surprising, as this is not necessarily something you would expect when working with such small microorganisms.”

Using a molecular technique called “DNA metabarcoding,” which can identify multiple organisms in a single sample, the researchers were able to identify the fungi present in green roof soils as well as the potential sources of these fungi. Many fungi came from the inoculum while other species arrived there by another vector such as the wind.

The co-authors say their study was different from most studies of this type because few studies track changes in the mycorrhizal community over time after inoculation and even fewer attempt to track the sources of the mycorrhizal pools. ‘species. The team also had a number of species in their green roof that likely arrived via unmeasured vectors such as birds, insects or even rats.

Nonetheless, the most diverse fungal communities were those that had been treated with the inoculum, illustrating how mycorrhizal fungi could be used to improve soil health in green roofs. The results suggest that active management of soil microbial communities is effective and worth the effort and resources in cities.

“Green roofs have a lifespan and are not always the self-sustaining ecosystems we think they are,” says lead author Bala Chaudhary, associate professor of environmental studies at Dartmouth. “They can be beneficial in urban areas but tend to lose effectiveness over time.”

While green roofs are marketed as “set it and forget it”, the co-authors explain that ecological thinking should be integrated into their design, construction and maintenance to maximize the benefits and role that green roofs play. green roofs in the climate resilience of urban areas. .

“Our cities could be a window to the future,” says Chaudhary. “They are experiencing the impacts of climate change – warming temperatures and increased droughts and floods – in intensified ways, making them an excellent microcosm to study some of these impacts underground.”