Chlorophyll fluorescence illuminates plant function

From left to right: Solar induced chlorophyll-a fluorescence can be seen with bare eyes after dissolving the chlorophyll from leaves into a solvent and placing the extract under direct sunlight. SIF can be measured at the plant, ecosystem (here: apple orchard), and global scales. Credit: Albert Porcar-Castell

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Chlorophyll, the green pigment found in plants and algae, emits faint red and far-red light when illuminated during photosynthesis. This so-called chlorophyll-a fluorescence conveys information about the instantaneous rate of photosynthesis, which provides an optical window that tracks plant functional and health status.

Although methods to measure and interpret chlorophyll-a fluorescence at the leaf and subcellular levels have been around for decades, it is only recently that chlorophyll fluorescence (known as solar-induced fluorescence, SIF) can be estimated and imaged at the ecosystem and regional scales.

Cutting edge SIF measurements are conducted with hyperspectral optical sensors mounted on towers, drones, aircraft, and even satellites. For example, the FLuorescence EXplorer (FLEX) satellite mission from the European Space Agency is scheduled for launch in 2024 and will provide global maps of SIF at a resolution of a few hundred meters.

These developments pave the way to multiple scientific and commercial applications in plant ecophysiology, ecology, biogeochemistry, as well as precision agriculture, and forestry.

Albert Porcar-Castell from the University of Helsinki said, excitingly, SIF opens up spatial and 3D photosynthesis studies in the field. This will help to resolve long-standing research questions related to the photosynthetic dynamics of the different parts of a plant or ecosystem in real-world conditions. SIF can also be applied in physiological phenotyping and pre-visual stress detection, which is a powerful tool for next-generation forest and crop management practices.

To meet these ambitious goals, multiscale and multidisciplinary collaborative studies are required. Expertise from plant biology, remote sensing, agronomy, and forestry should be fused to translate the information content of SIF into innovative applications capitalizing on insight across the molecular, leaf, and canopy scales.

Journal Information: Albert Porcar-Castell et al, Chlorophyll-a fluorescence illuminates a path connecting plant molecular biology to Earth-system science, Nature Plants (2021). DOI: 10.1038/s41477-021-00980-4