News Excerpt:

A study sought to establish whether regulating green roof soil bacteria may improve healthy urban soil growth, a methodology that could be used to increase climate resilience in cities.

What is a Green Roof?

• Green roofs are well-known as a sustainable construction practice.
• It refers to a roof covered with waterproof membranes with plants or trees suitable for the local climate and 3–15 inches of soil, sand, or gravel. 
• As the green roof is made up of plants and trees, it has similar benefits as trees including climate adaptation, mitigation, and urban biodiversity management.
• Compared to traditional roofs, green roofs can cut down building electricity consumption by 2%–6%, especially for summer cooling by maintaining temperature.
• These planted surfaces on building rooftops absorb excess stormwater, reduce energy consumption by insulating buildings, chill neighbourhoods, moderate urban heat islands, and provide urban homes for plants, pollinators, and wildlife.

Why the study?

• Despite the benefits, green roofs in the United States are often planted with non-native plants in sterile soils.
• Green roofs have a shelf life and they’re not always the self-sustaining ecosystems that people think.
• They can be beneficial to urban areas but tend to lose their efficacy over time.
• This study tries to prove that active management of soil microbial communities is effective and worth the effort and resources in cities.

Hypothesis: 

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

• They also compared the green roof fungal species identified to those present in the inoculum and the air using a molecular technique called “DNA metabarcoding.”
• Time Period: 2 years

Experiment:

The researchers added soil rich with native mycorrhizal fungi obtained from a locally restored prairie, referred to as “inoculum,” to the experimental green roof’s soil.

• Mycorrhizal fungi are well-known to live in roots and support plants in a symbiotic underground relationship, delivering nutrients and water to them in exchange for plant sugars.
• Mycorrhizal fungi could be particularly helpful to plants on green roofs that have to endure high temperatures, intense sun, and periodic flooding.

Findings:

• Active management of green roof mycorrhizal fungi accelerates soil development faster than if mycorrhizal fungal communities are left to passively reestablish on their own. 
• Green roofs treated with mycorrhizal fungi foster a more diverse soil community that is more likely to support long-term green roof sustainability.
• It illustrated how mycorrhizal fungi could 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.