Green roofs are becoming increasingly popular due to their benefits related to climate change adaptation, climate change mitigation and urban biodiversity management.
These green surfaces on building roofs absorb excess rainwater, reduce energy use by insulating buildings and cool neighborhoods, and mitigate urban heat islands while creating urban habitats for plants, pollinators and life. wild.
But in the United States, green roofs are typically planted with exotic plants in sterile soil, and their effectiveness diminishes over time. The right combination of soil and microorganisms could be a climate resilience tool for cities.
Microorganisms on green roofs
A Dartmouth-led research team wanted to find out whether managing soil microorganisms on green roofs could promote healthy urban soil development, a method that could be used to support climate resilience in cities.
The team created an experimental green roof in Chicago to test how soil amendment with native prairie microorganisms would change the soil microbial community over time. They were particularly interested in tracking the presence of beneficial fungi such as mycorrhizae.
Mycorrhizae are known to live in the roots and support plants in an underground symbiotic relationship, providing nutrients and water in exchange for plant sugars. Mycorrhizal fungi could be particularly useful for plants on green roofs that have to withstand high temperatures, intense sunlight and periodic waterlogging.
Native mycorrhizal fungi
The researchers added soil rich in native mycorrhizal fungi from a restored local grassland known as “Inoculum“, to the bottom of the experimental green roof. They planted inoculated, untreated soil with native prairie plants and typical greenroof succulents. For two years, the team tracked changes in the green roof’s mycorrhizal fungal community. They also compared the identified fungal species on green roofs with those in the inoculum and in the air.
Their results show that actively managing mycorrhizal fungi on green roofs accelerates soil development faster than allowing mycorrhizal fungal communities to passively re-establish themselves. 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 environment, we saw greater diversity in the fungal communities of the inoculated soilsaid lead author Paul Metzler, director of the Soil Ecology Laboratory in Dartmouth’s Department of Environmental Studies. “The sustained long-term effects of the inoculum were quite surprising, as this is not necessarily what one would expect when working with such small microorganisms.“.
Using a molecular technique called “DNA metabarcoding“, which allows for the identification of multiple organisms in one sample, the researchers were able to identify the fungi present in the soils of the green roofs, as well as the possible sources of these fungi. Many fungi came from the inoculum, while other species arrived via other vectors such as wind.
The co-authors say their study differs from most of its kind because few studies track changes in the mycorrhizal community over time after inoculation and even fewer attempt to trace the sources of species groups. The team also had several species on their green roof that were likely introduced via unmeasured vectors, such as birds, insects or even rats.
Soil health on green roofs
Nevertheless, the fungal communities treated with the inoculum were the most diverse, demonstrating how mycorrhizal fungi can be used to improve soil health on 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 for urban areas, but tend to become less effective over time“.
While green roofs are marketed with the slogan “set it and forget it,” the co-authors explain that to maximize the benefits and role of green roofs in the climate resilience of urban areas, green thinking must be incorporated into their planning, construction and maintenance.
“Our cities could be a window to the futuresays Chaudhary. “They are experiencing increased impacts of climate change (warmer temperatures and increasing droughts and floods), making them a great microcosm to study some of these impacts underground.“.
Metzler is available for comments at: [email protected]. Kelly Ksiazek-Mikenas of Elmhurst University was also a co-author of the study.
With information from: