Capitol News

Scientists at Michigan State University have published a study in New Phytologist revealing how Amazon rainforest canopy trees manage sunlight absorption. The research highlights the resilience of these trees to hot and dry conditions while offering insights into improving the monitoring of canopy health under extreme conditions. The study was funded by the National Science Foundation and NASA.

The research team, led by doctoral candidate Leonardo Ziccardi with Associate Professor Scott Stark from MSU's Department of Forestry, discovered that tropical trees act like giant solar antennas. They absorb significant amounts of light energy, which must be carefully managed. When excess energy is absorbed beyond what can be used for photosynthesis, it is dissipated as heat or re-emitted as light through chlorophyll fluorescence.

“It’s been a long journey,” said Ziccardi. “Since 2019, we’ve run multiple field campaigns across seasons, climbing giant trees in the heart of the Amazon to understand how these forests respond to environmental changes. We’ve spent hundreds of hours up in the canopy doing measurements — some of the most intense and rewarding work I’ve ever done.”

Ziccardi and his team used a handheld instrument called MultispeQ, developed at MSU by co-author David Kramer from the MSU-DOE Plant Research Laboratory, to measure leaf photosynthesis in natural settings. This allowed them to capture how leaves balance incoming light with their ability to photosynthesize or dissipate excess energy.

The findings offer a detailed view of how the Amazon canopy handles seasonal extremes. As greenhouse gases and deforestation lead to hotter and drier conditions, understanding how trees manage light energy becomes crucial for predicting their survival. These changes increase physiological stress due to more frequent extreme conditions related to lower soil water availability and increased sunlight exposure.

For the first time in the Amazon, this study revealed a three-phase response of leaves to rising light and drought conditions. Under low to moderate light, leaves balance energy use between photosynthesis and fluorescence. However, as stress increases, this balance breaks down; heat-protective mechanisms become overwhelmed, causing photosynthesis to drop while fluorescence spikes.

These findings have significant implications for scientists using satellite observations of solar-induced fluorescence (SIF) to monitor forest health. While SIF is often used as a proxy for photosynthesis, this study shows that they do not always correlate under high stress conditions. This could lead to overestimations of ecosystem productivity during droughts.