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Recently, I was reading the question "Photosynthesis - light intensity, particularly the answer, that states that different species require different intensity of light. My question is what is the lowest threshold of light intensity for photosynthesis of any species?

Specifically, how have that species adapted to take full advantage of the low intensity?

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    $\begingroup$ So you are asking about light needed for photosynthesis to take place, not the light intensity needed to sustain the plant? Since photosynthesis is an interaction between chlorophyll and single photons I would assume that photosynthetic reactions could take place with just single photons of suitable wavelength (i.e. at the limit of defining light intensity), but to measure this might be extremely hard in practice. The article Photosynthesis in the Abyss indicates that this might be the case, saying ... $\endgroup$
    – fileunderwater
    Commented Aug 30, 2013 at 10:52
  • $\begingroup$ @fileunderwater thank you for that! That is the kind of information I am after - and that is an amazing example. $\endgroup$
    – user3795
    Commented Aug 30, 2013 at 10:54
  • $\begingroup$ Reposted comment as answer since you found it interesting, and to make it more visible. $\endgroup$
    – fileunderwater
    Commented Aug 30, 2013 at 11:00

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Disclaimer: photosynthesis is not my field of expertise.

I assume you are asking about the amount of light needed for photosynthesis to take place, not the light intensity needed to sustain the plant? Since photosynthesis is an interaction between chlorophyll and single photons I would assume that photosynthetic reactions could take place with just single photons of suitable wavelength (i.e. at the limit of defining light intensity), but to measure this might be extremely hard in practice. The article Photosynthesis in the Abyss indicates that this might be the case, saying that in deep sea environments "A single molecule of bacteriochlorophyll receives a single photon only about once every 8 hours" (see also this popular science article). The conditions for deep sea photosynthesis is described in Beatty et al. (2005), which report photosynthesis by green sulfur bacteria at hydrothermal vents, where the only source of light is geothermal radiation.

However, as stated earlier, photosynthesis is not my subject field so I do not know how credible this information is.

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  • $\begingroup$ The answer was great, the additional references are brilliant. $\endgroup$
    – user3795
    Commented Aug 31, 2013 at 9:12
  • $\begingroup$ @UV-D Would be great with an answer from somebody working actively with photosynthesis though as a complement, e.g. some comparative results on how different species cope with low-light conditions. $\endgroup$
    – fileunderwater
    Commented Sep 1, 2013 at 9:12

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