Does photosynthesis occur only in the visible spectrum? If there is a way to completely remove all other electromagnetic bands from the sunlight, including infrared (IR), will photosynthesis continue to occur?

Is there any known plant (algae, fungi, bryophytes, pteridophytes, gymnosperms and angiosperms) that utilises the other wavelengths for photosynthesis?

  • $\begingroup$ Photosynthesis occurs at and around the absorption spectrum of chlorophyll, i.e. at green wavelengths, so in the visible spectrum. This does not mean that other wavelengths are not used, just less optimally. $\endgroup$
    – AliceD
    Jan 6 '15 at 4:41
  • $\begingroup$ @ChrisStronks Sorry, I started editing once I saw your comment. It seems your edit clashed with mine. Feel free to edit this version $\endgroup$
    – One Face
    Jan 6 '15 at 4:42

Photosynthesis only occurs in the visible light.have a look at the absorption spectra of the different pigments involved in photosynthesis, you see that all these pigments absorb light between 400 and 700nm (from a diagram from here):

enter image description here

You see that the absorption spectra of chlorophyll a and b are located from 400 to 500nm and again from 630 to 700nm. The maxima for both molecules are different so that the light is used more efficiently.

The other three important light harvesting pigments involved in photosynthesis (in cyanobacteria and plants) are: Beta Carotene, Phycoerythrin and Phycocyanin. These use different parts of the visible spectrum (hence the different color of cyanobacteria), but they still only use the visible part of the light between 400 and 700nm.

The reason for this can be seen in the figure when you look at the intensity of the sunlight (plotted in black). All photosynthesis occurs in the area of the highest intensity. Wavelengths shorter than 350nm are efficiently blocked by our atmosphere, wavelengths much longer are not transporting much energy.

To shortly answer your question: If we could "switch off" all other wavelengths from the spectrum, there would still be photosynthesis on earth.

  • $\begingroup$ Don't we need some infrared to keep the plan warm enough, as otherwise most plants just shut down. $\endgroup$ Jan 6 '15 at 16:59
  • $\begingroup$ I'm curious, what software do you use to generate the graph? $\endgroup$
    – Ooker
    Jan 6 '15 at 16:59
  • $\begingroup$ I haven't made this myself, the source is named above the figure (in brackets). $\endgroup$
    – Chris
    Jan 6 '15 at 17:09
  • $\begingroup$ @IanRingrose sort of? Infrared is more the mediator of heat than the provider. Warm things would emit it if it wasn't around, but a planet illuminated by only gamma rays would still be warm if it had an atmosphere to keep the heat in. It wouldn't exactly be a vacation spot. $\endgroup$
    – Resonating
    Jan 6 '15 at 18:28

Photosynthesis is nearly all visible light. There's usually not enough UV and thermodynamics more or less rules out infrared. Chris covered that pretty spectacularly, but that nearly is significant.

There is some evidence that certain kinds of fungi can use gamma rays or other ionizing radiation for energy, but they're not particularly common. Melanin is used instead of chlorophyll, but apparently 'tooling up' for radiosynthesis(is that a word?) is fairly hard on the cell. It was assumed the melanin was a protective pigment(like it is in humans) and produced only when necessary(also like humans), but these particular ones were discovered growing in the Chernobyl reactor and apparently evolved to continuously produce melanin and absorb ionizing radiation for food. They don't stop producing melanin even on the verge of starvation. Other melanized fungi live in high-radiation environments, like mountaintops and the poles, where there is more UV and cosmic rays and things.

Fun fact aside: Fossilized melanized fungal spores turn up at the K-T boundary when the earth had no magnetic field and therefore higher radiation flux at the surface (see paper linked above and Hulot & Gallet, 2003 for more).

  • 2
    $\begingroup$ +1 Interesting fact. The word is "radiotrophic" BTW. $\endgroup$
    Jan 6 '15 at 10:49
  • $\begingroup$ I would use radiosynthesis to describe the process of absorbing ionizing radiation for energy, and things that primarily do that for food as radiotrophic, but my spellcheck underlines both as 'not real words' and I'd never heard radiosynthesis before. Chemo/photosynthesis, sure. radiosynthesis no. $\endgroup$
    – Resonating
    Jan 6 '15 at 18:34
  • 1
    $\begingroup$ You are right, I forgot about this part. $\endgroup$
    – Chris
    Jan 6 '15 at 19:38
  • 3
    $\begingroup$ Do you have citation to the fun fact? Great additional answer. $\endgroup$ Jan 6 '15 at 22:49
  • 1
    $\begingroup$ Curiously enough, the paper about radiotrophic bacteria talks a little about that, but they cite in turn Hulot G, Gallet Y (2003) Do superchrons occur without any palaeomagnetic warning? Earth Planetary Sci. Lett. 210: 191–201. $\endgroup$
    – Resonating
    Jan 7 '15 at 5:30

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