Amazon rainforest trees are constantly exposed to intense sunlight, especially in the upper canopy, where the tallest trees tower nearly 200 feet above the ground.
A new study by researchers at Michigan State University has uncovered how these trees manage all that sunlight—revealing surprising strategies that help them survive heat and drought.
Their findings also highlight how scientists may need to rethink how we monitor the health of these forests from space.
Led by PhD student Leonardo Ziccardi and Associate Professor Scott Stark from MSU’s Department of Forestry, the research explored how canopy leaves handle the enormous amount of sunlight they absorb each day.
Like giant solar panels, these leaves take in sunlight to power photosynthesis—the process that helps trees grow and absorb carbon dioxide.
But when they take in more light than they can use, they must safely release the excess energy, either as heat or as a faint glow called chlorophyll fluorescence.
To measure this in the real world, Ziccardi and his team climbed massive trees deep in the central Amazon over the course of four years.
Using a portable device called the MultispeQ—developed at MSU—they measured how thousands of leaves handled light under different conditions.
This work created a one-of-a-kind dataset, giving scientists a clearer picture of how the forest responds to seasonal changes and rising climate stress.
As climate change makes the Amazon hotter and drier, with fewer clouds and more direct sunlight, it’s critical to understand how trees are coping.
The study found that many canopy leaves continue photosynthesizing even in tough conditions—but only by working harder to release the extra energy they can’t use. This means they channel more energy into protective pathways that prevent damage, like releasing heat or light.
The researchers discovered that leaves follow a three-step pattern as light and drought levels increase.
At first, photosynthesis and fluorescence rise together. But as conditions become more extreme, the balance shifts. The heat-protective systems get overloaded, photosynthesis drops, and fluorescence can suddenly spike—signaling that the leaves may be under serious stress or even suffering damage.
This finding has big implications for how scientists monitor the Amazon using satellites. Satellites can detect solar-induced fluorescence (SIF), which is often used as a sign of plant productivity. However, this study shows that SIF doesn’t always mean a tree is photosynthesizing more. In fact, during droughts, leaves might glow brighter even while their ability to turn sunlight into energy is falling.
By uncovering how trees juggle light and stress, this research gives us better tools to track the health of the Amazon—a forest that plays a vital role in regulating Earth’s climate.
