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What is in a Plant Physiologist’s Toolkit?: Measuring Photosynthesis

August 23, 2021


If you are a plant lover, chances are you often find yourself thinking about photosynthesis in some way. You may move a house plant to a bright window so that it can use energy from light to fix carbon from the atmosphere and use that carbon to build tissues as it grows. Or, perhaps you want your vegetable garden to give you delicious tomatoes, so you choose the best conditions to maximize fruit production. Plant physiologists are very interested in the rate of photosynthesis and we love to assign a value to it. We use this information to estimate the range of photosynthetic rates for a species or population or, we can use those values to understand how photosynthetic rate changes with environmental stressors like drought or frost.  

I have found that one of the most common questions I get is, “How do you measure photosynthesis”? This is a great question! One of the tools we have in our physiological toolkit is the LICOR 6800, a portable photosynthesis system. The photosynthesis system uses a set of IRGAs (infrared gas analyzers) to compare the levels of CO2 between a reference chamber with a known amount of CO2 and a sample chamber that mixes with the gases from the chamber containing a leaf. As a plant photosynthesizes, it draws down the carbon dioxide in the sample chamber making the CO2 lower relative to the reference chamber. The value that we report is really one aspect of the whole photosynthetic process, the uptake and absorption of CO2 into the plant, known as the assimilation rate.

The LICOR allows us to strictly control the levels of CO2 in the reference chamber, the light level, temperature, and humidity. The system removes all ambient CO2 and adds in a known amount via a food grade CO2 cartridge. It can also remove all ambient humidity and add in a known moisture level. This awesome portable tool is an incredibly powerful tool that allows us to report the function of plants in many environmental conditions!

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