Researchers have created a global map of the fluorescence emitted by land-based plants during photosynthesis. This subtle glow at certain wavelengths could serve as an early warning system for plant stress and help scientists better understand Earth's carbon cycle.
During photosynthesis, plants use chlorophyll and solar energy to convert carbon dioxide, water and other nutrients into sugars and other organic compounds. Together, these chemical reactions emit low levels of fluorescent light at wavelengths between 650 nm (red) and 800 nm (near-infrared). But this feeble glow typically goes unnoticed because it is swamped by sunlight reflected from the plant, says Joanna Joiner, a remote-sensing analyst at NASA's Goddard Space Flight Center in Greenbelt, Maryland. However, at some wavelengths — particularly the ones at which most or all of the radiation is absorbed by ionized atoms in the Sun's outer atmosphere — the fluorescence shines forth unmasked. And lab tests suggest that when sunlight is bright, the strength of fluorescence is a good indicator of how much photosynthesis is taking place.
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