Street lights are adversely affecting plants

Chuck Bednar for redOrbit.com – @BednarChuck

Street lamps and other nighttime sources of light have become common and essential for life in the city, but could they be adversely affecting plant life? According to the authors of a new study published Monday in the Philosophical Transactions of the Royal Society B, the answer is yes.

In their new study, researchers from the University of Exeter’s Environment and Sustainability Institute (ESI) demonstrate that light pollution from these objects can impact the environment of exposed plants in complex and difficult-to-predict ways, including their growth and flowering.

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Artificial light can also affect the number of insects that depend on those plants for food, the study authors explained, and due to the widespread global use of devices such as street lights, there are serious concerns that these ecological impacts could be widespread in nature.

“These are the first findings from major long-term experiments being funded by the European Research Council, and already reveal how profound the impacts of artificial nighttime lighting can be on even simple communities of organisms,” ESI director Professor Kevin Gaston, one of the authors of the next study, explained over the weekend in a statement.

Lighting up our lives at a cost

Professor Gaston and his colleagues conducted a series of nighttime experiments in which they simulated the effects of artificial street lighting on synthetic grassland plots that each contained a community of invertebrates. The plants used were pea aphids (Acyrthosiphon pisum).

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The plots were exposed to two different types of light treatment: a white light similar to newer commercial LED street lighting systems, and an amber one which simulated sodium street lamps still commonly used in the UK. Furthermore, the effects of both top-down (predator driven) and bottom-up (food or resource limited) light on the plants’ population density were examined.

The lower-intensity amber light was found to inhibit flowering in a wild relative of peas and beans known as the greater bird’s foot trefoil, which serves as a key source of food for pea aphids in grasslands and road verges. The aphids feed on those flowering shoots throughout the summer, and as a result, the aphid numbers were significantly reduced in mid-August due to limited food availability under the light treatment.

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“Our results suggest that by lighting up our nighttime environment, we trigger complex effects on natural food webs,” said Dr. Jonathan Bennie, an associate research fellow at the ESI and one of the study’s authors. “While we are all aware that street lights often attract insects at night, we show that they may have more permanent, widespread impacts on wildlife and ecosystems.”

While they wrote that they found “no evidence” supporting negative impact from the top-down experiments, the researchers explained that the results of the bottom-up experiments “suggest that physiological effects of light on a plant species within a diverse plant community can have detectable demographic effects on a specialist herbivore.”

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