Some plants may worsen air pollution on a warming planet: Study

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, a study shows.

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?' said Tom Sharkey, a professor at Michigan State University in the US.

'Those are really the fundamental questions driving this work. The more we understand, the more effectively we can answer them,' Sharkey said.

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, the researchers said.

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, they said.

Prior to the latest study published in the journal Proceedings of the National Academy of Sciences, the researchers understood that certain plants produce isoprene as they carry out photosynthesis.

They also knew the changes that the planet is facing were having competing effects on isoprene production.

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, the researchers said.

'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. And finally, we have the answer,' Sahu added.

The researchers noted that the temperature effect trumps the carbon dioxide (CO2) effect.

'By the time you're at 95 degrees Fahrenheit—35 degrees Celsius—there's basically no CO2 suppression. Isoprene is pouring out like crazy,' said Sahu.

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.

The discovery will help researchers better anticipate how much isoprene plants will emit in the future and better prepare for the impacts of that.

However, the researchers also hope it can help inform the choices people and communities make in the meantime.