Photosynthesis, Fluorescence, and Food, Oh My!

The world’s population is growing exponentially, and with it, so is the demand for food. Photosynthesis is the fundamental process required to produce our food and oxygen – plants use the process to produce sugars and chemical energy needed for growth. We then either eat the plants directly or indirectly (by consuming animals or fungi that feed on the plants). So what is photosynthesis exactly?

Photosynthesis is the process by which plants convert sunlight and carbon dioxide in the air into sugars. Plants have specialized structures called chloroplasts (see image below) in their leaves that absorb light and store the energy as sugars. The light is absorbed using pigments called chlorophylls – they are what make plants green. We depend on photosynthesis for almost everything we do: not only is it the ultimate source of our food and oxygen, it is also the source of our gasoline – photosynthesizing plants were turned into fossil fuels over millions of year in the ground. Given the dependence of human civilization on photosynthesis, it is natural to ask: how much photosynthesis happens on the planet? The answer to this question has implications for the human population limit, and general quality of life.

chloroplast

Guanter et al. (Guanter et al., 2014, PNAS 111: E1325-E1333) provide the first step toward being able to answer this question. Up until now, estimating photosynthesis on a global scale required very complicated mathematical models. In the study by Guanter et al., they use satellites to measure a phenomenon known as sun-induced fluorescence.

When the chlorophylls found in plants absorb light, there are several possible paths the light energy can take: it can be used in photosynthesis, released as heat (diverting energy from photosynthesis), or the energy can be re-emitted as light (called fluorescence). All three of these paths are used when a plant is in the light. The interesting thing about fluorescence is that the light is always a very specific set of colours. The authors capitalize on this by using a satellite that can detect light of the colours associated with fluorescence in plants. Their primary finding is that the amount of fluorescence in global croplands is tightly associated with the amount of photosynthesis occurring in those regions – however the mathematical models underestimate the amount of photosynthesis in these regions.

This study demonstrates that we might be able to keep stock of photosynthesis worldwide simply by using satellites to measure fluorescence. The consequence of this is that we could keep an eye on global food production in near-real time, which would at least allow pre-emptive preparations against food shortages.

Hopefully by this point I have convinced you that photosynthesis is vitally important to human civilization (and to the planet as a whole). If you are interested in a more detailed explanation of photosynthesis, check back here as I intend to post an in-depth explanation of how photosynthesis works.

Stay safe and stay informed,
Joe

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