The post-apocalyptic science fiction novel Dark Universe by Daniel F. Galouye has some plants living inside bunkers that use infrared light for photosynthesis. There are speculations that extraterrestrial plants might use the same trick on planets orbiting red dwarfs and that their leaves would be totally black. Would this type of photosynthesis be possible and are there any plants on low-light environments from Earth that might do this already?
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3 Answers
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There is an algea that uses IR:
The newfound pigment, dubbed chlorophyll f, absorbs light most efficiently at a wavelength around 706 nanometers, just beyond the red end of the visible spectrum, researchers report online August 19 in Science. This unique absorbance appears to occur thanks to a chemical decoration known as a formyl group on the chlorophyll’s carbon number two. That chemical tweak probably allows the algaelike organism that makes chlorophyll f to conduct photosynthesis while living beneath other photosynthesizers that capture all the other usable light. https://www.wired.com/2010/08/infrared-chlorophyl/
Infra red can't directly disassociate CO2, it's too low in energy, so that it represents a relatively inefficient and complex chemical pathway for photosynthesis compared to conventional. Research shows that multiple IR photons can be converted to other photons using photon up-conversion, and then used for photosynthesis http://www.sciencedirect.com/science/article/pii/S0360319912001838
here is the most clear summary of why IR is absorbed as heat by water, visible light is gentle and goes through water and excites electrons to do chemical reactions, and UV is too energetic. https://www.reddit.com/r/askscience/comments/14jsms/can_plants_perform_photosynthesis_using_non/
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I would hardly ever say never where biology is concerned. In this case that utilizing red rather than blue light for a plant would require many of the basic assumptions of photosynthesis in terrestrial plants to be revised, but since we're talking about another planet, that might not really be an issue.
If we are asking only about how we could change our plants to work with IR light, I'd say that might take a few hundred million years of selection and it's harder to imagine.
Firstly photosynthesis in another planet doesn't have to fix carbon or produce oxygen - both of these chemical processes utilize the relatively greater energy produced in blue and red light photosynthesis we see in plants here.
Secondly using IR would have its particular questions associated with it. In this case the energy quanta are very small and in fact in the same range as chemical bond vibrational energies. Such energy might be hard to capture with any efficiency since simple heat would tend to compete with the photon, so this would work better if the entire system were at a relatively low temperature.
The leaves could be black or they could be completely clear by the way.
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$\begingroup$ "utilizing red rather than blue light for a plant would require many of the basic assumptions of photosynthesis" Both answers to Are two colors (red + blue) necessary for LED grow lights, or would either color be sufficient? indicate that it's primarily red light that's useful in photosynthesis and blue light for phototropism. Yes blue light can excite chlorophyl as well, but all you need is circa 680 nm to make it work. That's already almost infrared if we used 700 nm as the boundary. $\endgroup$– uhohCommented Jul 19, 2023 at 13:56
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$\begingroup$ Several other answers provide actual examples where wavelengths longer than 700 nm are already in use by life on Earth for photosynthesis, so I think this needs some rewriting to align with actual facts. I noticed that you don't draw from any supporting sources for these assertions. $\endgroup$– uhohCommented Jul 19, 2023 at 14:02
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Photosynthetic bacteria can use infrared light down to 1050 nm (Blastochloris) for photosynthesis.
Oxygenic photosynthesis seems to have limit at about 750 nm.
I think there are organisms that can use longer wavelengths for both oxygenic and anoxygenic photosynthesis. It is just they have not been looked for in the right way.
Here are some papers of mine. 92). RITCHIE, R.J., LARKUM, A.W.D. and RIBAS, A. (2017) Could Photosynthesis function on Proxima Centauri b? International Journal of Astrobiology 0(0): 1 –30 doi: 10.1017/S1473550417000167. 93). LARKUM, A.W.D., RITCHIE, R.J., and RAVEN, J.A. (2018). REVIEW: Living off the Sun: chlorophylls, bacteriochlorophylls and rhodopsins. Photosynthetica 56: 11–43, DOI: 10.1007/s11099-018-0792-x
