Should We Cut Down All the Oak Trees? The Unexpected Link Between Trees and Air Pollution

A Study on the Complex Relationship between Oaks and the Environment

It’s a simple question that sounds a little like a modest proposal.

Introduction

“Should we cut down all the oak trees?” asked Tom Sharkey, a University Distinguished Professor in the Plant Resilience Institute at Michigan State University.

Sharkey also works at the MSU Department of Energy Plant Research Laboratory and in the Department of Biochemistry and Molecular Biology.

To be clear, Sharkey wasn’t sincerely suggesting that we should cut down all the oaks. Still, his question was an earnest one, prompted by his team’s latest research, which was recently published in the scientific journal Proceedings of the National Academy of Sciences.

The Impact of Isoprene on Air Quality

The team discovered that, on a warming planet, plants like oaks and poplars will emit more of a compound that exacerbates poor air quality, contributing to problematic particulate matter and low-atmosphere ozone.

The rub is that the same compound, called isoprene, can also improve the quality of clean air while making plants more resistant to stressors including insects and high temperatures.

“Do we want plants to make more isoprene so they’re more resilient, or do we want them making less so it’s not making air pollution worse? What’s the right balance?” Sharkey asked. “Those are really the fundamental questions driving this work. The more we understand, the more effectively we can answer them.”

Spotlight on Isoprene

Sharkey has been studying isoprene and how plants produce it since the 1970s when he was a doctoral student at Michigan State.

Isoprene from plants is the second-highest emitted hydrocarbon on Earth, only behind methane emissions from human activity. Yet most people have never heard of it, Sharkey said.

“It’s been behind the scenes for a long time, but it’s incredibly important,” Sharkey said.

It gained a little notoriety in the 1980s when then-president Ronald Reagan falsely claimed trees were producing more air pollution than automobiles. Yet there was a kernel of truth in that assertion.

Isoprene interacts with nitrogen oxide compounds found in air pollution produced by coal-fired power plants and internal combustion engines in vehicles. These reactions create ozone, aerosols, and other byproducts that are unhealthy for both humans and plants.

“There’s this interesting phenomenon where you have air moving across a city landscape, picking up nitrogen oxides, then moving over a forest to give you this toxic brew,” Sharkey said. “The air quality downwind of a city is often worse than the air quality in the city itself.”

Understanding Isoprene Production

Now, with support from the National Science Foundation, Sharkey and his team are working to better understand the biomolecular processes plants use to make isoprene. The researchers are particularly interested in how those processes are affected by the environment, especially in the face of climate change.

Prior to the team’s new publication, researchers understood that certain plants produce isoprene as they carry out photosynthesis. They also knew the changes that the planet was facing were having competing effects on isoprene production.

That is, increasing carbon dioxide in the atmosphere drives the rate down while increasing temperatures accelerate the rate. One of the questions behind the MSU team’s new publication was essentially which one of these effects will win out.

“We were looking for a regulation point in the isoprene’s biosynthesis pathway under high carbon dioxide,” said Abira Sahu, the lead author of the new report and a postdoctoral research associate in Sharkey’s research group.

“Scientists have been trying to find this for a long time,” Sahu said. “And, finally, we have the answer.”

“For the biologists out there, the crux of the paper is that we identified the specific reaction slowed by carbon dioxide, CO2,” Sharkey said.

“With that, we can say the temperature effect trumps the CO2 effect,” he said. “By the time you’re at 95 degrees Fahrenheit — 35 degrees Celsius — there’s basically no CO2 suppression. Isoprene is pouring out like crazy.”

In their experiments, which used poplar plants, the team also found that when a leaf experienced warming of 10 degrees Celsius, its isoprene emission increased more than tenfold, Sahu said.

“Working with Tom, you realize plants really do emit a lot of isoprene,” said Mohammad Mostofa, an assistant professor who works in Sharkey’s lab and was another author of the new report.

Implications and Recommendations

The discovery will help researchers better anticipate how much isoprene plants will emit in the future and better prepare for the impacts of that. But the researchers also hope it can help inform the choices people and communities make in the meantime.

“We could be doing a better job,” Mostofa said.

At a place like MSU, which is home to more than 20,000 trees, that could mean planting fewer oaks in the future to limit isoprene emissions.

As for what we do about the trees already emitting isoprene, Sharkey does have an idea that doesn’t involve cutting them down.

SDGs, Targets, and Indicators

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 3: Good Health and Well-being
• SDG 7: Affordable and Clean Energy
• SDG 11: Sustainable Cities and Communities
• SDG 13: Climate Action
• SDG 15: Life on Land

2. What specific targets under those SDGs can be identified based on the article’s content?

• SDG 3.9: By 2030, substantially reduce the number of deaths and illnesses from hazardous chemicals and air, water, and soil pollution and contamination.
• SDG 7.2: By 2030, increase substantially the share of renewable energy in the global energy mix.
• SDG 11.6: By 2030, reduce the adverse per capita environmental impact of cities, including by paying special attention to air quality and municipal and other waste management.
• SDG 13.2: Integrate climate change measures into national policies, strategies, and planning.
• SDG 15.2: By 2020, promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests, and substantially increase afforestation and reforestation globally.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Indicator for SDG 3.9: Number of deaths and illnesses attributed to air pollution.
• Indicator for SDG 7.2: Share of renewable energy in the global energy mix.
• Indicator for SDG 11.6: Air quality index in cities.
• Indicator for SDG 13.2: Integration of climate change measures in national policies and plans.
• Indicator for SDG 15.2: Forest area as a proportion of total land area.

Table: SDGs, Targets, and Indicators

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Source: scitechdaily.com

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