Green roofs have gained popularity due to their numerous benefits, including climate adaptation, mitigation, and urban biodiversity management. These vegetated surfaces on building rooftops absorb excess stormwater, reduce energy use by insulating buildings, cool neighborhoods, and create urban habitats for plants, pollinators, and wildlife.
However, in the United States, green roofs are typically planted with non-native plants in sterile soils, which leads to a decline in their effectiveness over time. To address this issue, a research team led by Dartmouth University conducted a study to determine if managing green roof soil microbes could enhance healthy soil development and support climate resilience in cities.
The team established an experimental green roof in Chicago to investigate how enriching the soil with native prairie microbes would impact the soil microbial community over time, with a specific focus on beneficial mycorrhizal fungi. Mycorrhizal fungi are known to form a symbiotic relationship with plant roots, providing them with nutrients and water in exchange for plant sugars. These fungi could be particularly beneficial for plants in green roofs, which face challenges such as high temperatures, intense sun, and periodic flooding.
The researchers added soil rich in native mycorrhizal fungi obtained from a local restored prairie, referred to as “inoculum,” to the experimental green roof’s soil. They then planted the inoculated and untreated soil with native prairie plants and green roof succulents.
Over a two-year period, the team observed changes in the mycorrhizal fungal community of the green roof. They compared the identified fungal species in the green roof soil to those present in the inoculum and in the air. The findings revealed that actively managing green roof mycorrhizal fungi accelerated soil development compared to passive reestablishment. Green roofs treated with mycorrhizal fungi fostered a more diverse soil community, which is crucial for long-term green roof sustainability.
The researchers used a molecular technique called “DNA metabarcoding” to identify the fungi present in the green roof soils and determine their potential sources. They found that many fungi originated from the inoculum, while others were likely introduced through vectors such as wind or animals.
The study’s authors noted that their research was unique as it tracked mycorrhizal community shifts over time and attempted to identify the sources of fungal species. They also highlighted the importance of incorporating ecological considerations into the design, construction, and maintenance of green roofs to maximize their benefits and contribute to urban climate resilience.
Green roofs are often marketed as self-sustaining ecosystems, but they can lose their efficacy over time. Therefore, the study suggests that active management of soil microbial communities, particularly mycorrhizal fungi, is essential for maintaining the health and sustainability of green roofs.
The research team believes that cities can serve as valuable microcosms to study the impacts of climate change on urban areas, including the effects on soil health. By understanding these impacts, cities can implement strategies to enhance climate resilience.
The study, titled “Tracking arbuscular mycorrhizal fungi to their source: active inoculation and passive dispersal differentially affect community assembly in urban soils,” was published in the New Phytologist journal.
Provided by Dartmouth College, the study highlights the importance of actively managing soil microbial communities in green roofs to improve their sustainability and contribute to urban climate resilience.
