Why “Leaky” Plants Could Accelerate Climate Change

The fate of our planet may hinge on the health of its plants. Dr. Sean Michaletz, a newly appointed Sloan Research Fellow in UBC’s Department of Botany, is reexamining how plants respond to heat. His findings cast doubt on long-standing assumptions about plant water loss and could reshape climate models.

The Role of Plants in Climate Change

Plants are integral to Earth’s biosphere. During photosynthesis, they absorb carbon dioxide through microscopic pores in their leaves and release oxygen and water vapor. As carbon dioxide is a major contributor to global warming, understanding the impact of heat on photosynthesis is essential for accurate climate predictions.

When temperatures soar, plants continue to lose water but struggle to absorb carbon dioxide, reducing their capacity for photosynthesis. In extreme heat, they might even switch from carbon sinks to carbon sources, further escalating climate change.

Quantifying the Impact of Heat Stress

A single leaf exposed to 50 °C could lose about one-third of a teaspoon of water daily through its cuticle. Scaling this up to entire forests highlights a significant gap in our current climate models, which may underestimate the effects of global warming on water and carbon cycles.

Researching Plant Tolerance Limits

In a study involving 200 plant species in Vancouver, Dr. Michaletz found that photosynthesis begins to deteriorate between 40 and 51 °C. During the 2021 heat dome, temperatures spiked to an alarming 49.6 °C, pushing many plants to their limits.

Continuing research suggests that 60 °C may be the maximum temperature plants can withstand. Beyond this point, proteins break down, leading to cell damage and death. Few desert or tropical species have ever been observed surviving such extreme conditions.

The Carbon Sink to Carbon Source Tipping Point

Scientists are working to identify the temperature at which Earth’s vegetation shifts from absorbing more carbon dioxide than it releases to becoming a net carbon emitter. Dr. Michaletz estimates this threshold could be around 30 °C, though many variables, such as microclimates and water availability, require further study.

Given that global temperatures have already averaged 16 °C, these limits are becoming increasingly relevant for predicting climate feedback loops and the future of Earth’s ecosystems.

Lessons from Human-Made Biospheres

Dr. Michaletz gained insights into plant responses under extreme conditions while working at Biosphere 2, a facility originally designed to test the feasibility of a self-sustaining, closed ecological system. The project aimed to simulate Earth’s systems, with a long-term goal of conducting similar experiments in space.

Although the initial experiment led to challenges like carbon dioxide buildup and psychological stress within the biospherians, Biosphere 2 eventually became a research and education center. There, Dr. Michaletz studied how plants respond to high temperatures in controlled environments.

Adapting to a Warmer World

Plants have endured climate shifts for millions of years, each species with unique adaptations. While some can tolerate higher temperatures better than others, the precise limits remain uncertain. Recent measurements suggest that we may be closer to these thresholds than previously thought.

Understanding how plants withstand heat stress is crucial for predicting the fate of Earth’s ecosystems in a warming world. This knowledge can inform strategies to protect and enhance carbon sinks, ensuring that plants continue fulfilling their vital role in regulating global temperatures.