Plants may stop absorbing carbon if temperatures continue to rise

The natural world has long adapted to Earth’s changing climate, but there are limits to what living organisms can withstand. Plants, in particular, play a crucial role in maintaining the planet’s balance by absorbing carbon dioxide and releasing oxygen.

However, new research suggests that rising temperatures may push plants beyond their limits, altering their ability to regulate the environment.

Scientists have traditionally believed that plants conserve water by closing their pores during extreme heat.

But Dr. Sean Michaletz, a botany professor at the University of British Columbia, has uncovered a surprising reality.

His research suggests that plants lose more water than expected, potentially weakening their role in climate regulation. If these findings are accurate, they could reshape how we predict future warming.

Plants help control carbon and water cycles

Plants are essential to life on Earth. Through photosynthesis, they take in carbon dioxide, convert it into energy, and release oxygen.

This process allows them to function as a carbon sink, absorbing greenhouse gases that would otherwise contribute to global warming.

In addition to their role in carbon absorption, plants regulate the water cycle. They release water vapor into the atmosphere, which helps cool the planet and maintain humidity levels.

However, as temperatures rise, this delicate balance may be shifting in unexpected ways.

Dr. Michaletz’s research suggests that rising heat forces plants to lose more water through their cuticle, a waxy layer on their leaves.

Unlike their pores, which can close to prevent water loss, the cuticle remains open. The thinner the cuticle, the more water a plant loses.

This process could reduce photosynthesis, limit carbon absorption, and even turn plants into carbon sources under extreme conditions.

Hidden risk of plant water loss

For decades, scientists assumed that plants primarily lost water through their pores, which could close during dry or hot conditions.

This belief shaped climate models and water cycle predictions. However, new findings indicate that cuticle-based water loss may be more significant than previously thought.

“When temperatures rise, plants lose more water through their cuticle than through their pores,” explained Dr. Michaletz. “This limits their ability to absorb carbon dioxide and reduces their role as a carbon sink.”

In extreme heat, plants may struggle to maintain photosynthesis, absorbing less carbon while continuing to release water.

If temperatures climb too high, forests and other ecosystems could shift from storing carbon to emitting it. This shift would accelerate climate change and disrupt global ecosystems.

Dr. Michaletz estimates that a single medium-sized leaf exposed to 50°C could lose about one-third of a teaspoon of water per day through its cuticle.

Scaled up to an entire forest, this effect could significantly alter global water and carbon cycles.

Current climate models may underestimate this impact, leading scientists to reassess predictions for future warming.

Extreme heat can make plants stop working

Not all plants respond to heat in the same way. Some species can tolerate extreme temperatures, while others begin to suffer as soon as conditions become too warm.

A study conducted in Vancouver examined 200 plant species to determine their heat tolerance.

“Our research suggests that photosynthesis starts to break down between 40 and 51°C,” said Dr. Michaletz. “During the 2021 heat dome, temperatures soared to 49.6°C, pushing plants to their limits.”

If temperatures continue rising, plants could reach a critical breaking point. The research team estimates that 60°C may be the maximum temperature plants can survive.

Beyond this threshold, proteins inside plant cells break down, leading to irreversible damage and eventual death.

While some desert and tropical plants have evolved to withstand extreme heat, most species do not have the same resilience.

Plants may turn into carbon sources

Understanding how heat affects plant life is essential for predicting climate change. If plants reach their temperature limits, they may stop absorbing carbon dioxide and instead release it, contributing to warming rather than slowing it.

“Globally, researchers are working to determine the ‘tipping point’ where Earth’s vegetation releases more carbon dioxide than it absorbs, switching from a carbon sink to a carbon source,” said Dr. Michaletz.

“Our estimates suggest this could happen around 30°C, though key uncertainties remain – especially how microclimates and water availability affect photosynthesis under extreme heat.”

With Earth’s average temperature already at 16°C, this threshold may be closer than expected. If plant ecosystems begin releasing more carbon than they store, global temperatures could rise even faster than current models predict.

Lessons from Biosphere 2

The relationship between plants and the environment has long fascinated scientists, leading to experiments that test how vegetation responds to extreme conditions.

One of the most ambitious projects in ecological research was Biosphere 2, an enclosed facility designed to simulate an independent ecosystem.

As a postdoctoral researcher, Dr. Michaletz worked at Biosphere 2, which was originally created as a self-sustaining environment.

Scientists, known as biospherians, were sealed inside to see if humans could survive without external oxygen or supplies.

“Biosphere 2 later transitioned into a research and public education center, where I studied how high temperatures affect plants in its experimental rainforest,” said Dr. Michaletz.

The original experiment revealed unexpected challenges. Carbon dioxide levels rose due to chemical reactions within the facility, and prolonged isolation caused psychological stress among participants.

These unexpected results highlighted the complexities of maintaining an artificial environment.

How close are we to the limit?

Plants have survived shifts in climate for millions of years, but they are not invincible.

They have upper limits, set by the physical laws governing their biological processes. While some plants have adapted to survive heat stress, many others cannot withstand prolonged extreme temperatures.

Scientists are now working to pinpoint exactly when and where vegetation will begin to struggle under rising global temperatures.

Some recent measurements suggest that plants may already be approaching dangerous heat thresholds.

If global warming continues unchecked, plants may lose their ability to regulate the carbon in the environment, triggering a chain reaction of climate feedback loops.

The question now is not whether plants will be affected by rising temperatures, but how soon the consequences will be felt.

Understanding these limits is crucial for predicting the future of Earth’s ecosystems and the role plants will play in a rapidly warming world.

The study is published in the journal New Phytologist.

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