At what stage in plants, a burst of light has the most effect on future growth

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Curiosity Science Biology and Medicine At what stage in plants, a burst of light has the most effect on future growth

  • A friend of mine has observed that very strong blue led light (440nm) shone onto a small tree for around a minute caused the tree to grow much more quickly than those around it. I have a few questions related to this observation, and applications to crop production. First of all, does this observation make sense? Can plants use extra light in intensities they would normally never experience? When in a crop’s life cycle would extra light make the biggest difference in yield? Would this vary by crop, and how much would it vary? Also, what wavelength would be optimal if you were just going to flash the crops with it for around a minute?

    – Question by Simon via the Ask a science question page.

  • Your friend’s observation makes sense. Take a look at the absorption spectra of chlorophyll.

    The absorption spectra of chlorophyll shown as a graph.

    Daniele Pugliesi | CC BY-SA 3.0

    In the green range, the absorption rate is relatively low for the primary pigments chlorophyll b and chlorophyll a, which means the leaf reflects all the green light (the reason why plants appear green).

    But in the violet and red ranges, the absorption peaks and chlorophyll benefit the most. And your 440 nm blue light happens to fall under that spectral range called the photosynthetically active radiation (400 to 500 nm and 600 to 700 nm – your optimal wavelength), which promotes photosynthesis in plants.

    And to back your friend’s observation, here is a study on how the removal of green and near-UV radiation promotes plant and algae growth with visible improvements. Most of the plants have shown positive growth characteristics without the green light. For most of the plants, you could try it right from the germination phase.

    But mind the fact that plants have other pigments that benefit from the green light too. Also, as the green light penetrates deep into the leaves than the red and the blue regions, it enables the chloroplasts that are away from the illuminated surface to promote photosynthesis. More on this, here and here.

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