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How to Grow a Green Roof

ByAllison EckNOVA NextNOVA Next

Green rooftops aren’t just verdant escapes for urban dwellers. For the past two years, New York City

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Mayor Michael Bloomberg’s PlaNYC initiative has offered tax abatements for green roof construction projects, which help stabilize building temperatures and manage stormwater runoff. Many of these rooftops are populated with sedum, a plant that’s resilient to wind and UV rays, but, unfortunately, can sometimes make buildings hotter by absorbing heat rather than reflecting it. So what’s a good alternative? The answer might lie in the soil—not the plants themselves. Here’s Amy Kraft writing for Scientific American:

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Krista McGuire has taken sedum’s inadequacy as a challenge. The assistant professor of biological sciences at Barnard College wanted to see if a variety of native plants could survive on green roofs and how well they would deliver the desired benefits. Since 2010, the year Bloomberg announced his green roof initiative, McGuire has been comparing soil samples from 10 roofs planted with native vegetation with soil from five city parks spanning New York’s five boroughs, seeking to identify the microbial communities that thrive on green roofs to better to understand how healthy rooftop ecosystems sustain themselves.

Her study, published in PLoS ONE last April, found that green roofs have distinct fungal communities that help plants to thrive in harsh, polluted environments and filter heavy metals. On average, 109 different types of fungi were present on each roof including Pseudallescheria fimeti , a fungus that grows in polluted soils and human-dominated environments. Rooftop soil also contained fungi from the genus

Peyronellaea, which live in the tissues of plants to help them take in nutrients.

Her study might be a step in right direction:

“In the long term, this information may help individuals decide which types of soil microbes to amend on their green roofs, so that they can maximize plant survival and minimize management,” she says.

This discovery is a variation on last week’s ; a study published in Ecology Letters found that subterranean fungal networks help plants warn each other against impending aphid attacks.

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