[thedoc (OP)]

If the sun is shining on the moon, and it’s a full moon, can plants photosynthesise with the reflected light?  If so, can they survive on that light alone?
Asked by Pete Charakas, Minneapolis

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[thedoc (OP)]

We put this question to Howard Griffiths, at the department of Plant Sciences, Cambridge University.

When I was first thrown this question about the role of moonlight in photosynthesis my initial response was not a chance! Because the light intensity that we get reflected off the moon is an order of 100-1000 times too little to support photosynthesis in most terrestrial pot plants and plants we have in our garden. However, I did a little bit of digging around and I looked at some latest analysis of photosynthesis rates in algae. Amazingly enough it does seem that some groups of very small phytoplankton might be able to photosynthesise using the light from the moon provided that it was in the tropics and provided that at wasn’t being attenuated by a water column which tends to absorb light exponentially. So the answer is still probably no because, obviously phytoplankton grow in a water column so they’re not really likely to be able to pick up the light intensity.

However, it also opens up a number of intriguing questions because plants do certainly try to avoid the light from the moon. I’m sure many of you are familiar with the folding of leaves that we see in the clover growing in your lawns and lots of plants in the garden fold up their leaves at night. Darwin was interested in this and thought that it was to do with the leaves trying to maintain their heat balance at night. What we think is happening now is that the leaves are trying to avoid moonlight so as to prevent their circadian rhythms being disrupted by those very light intensities because they certainly do respond to moonlight. In fact, it’s now known that lots of animals – animals as diverse as snakes and crocodiles and a whole array of plants and different systems including humans – are highly sensitive to moonlight and the way that it can interrupt our circadian control and our sensing of day length.

[paul.fr]

moonlight is 1/50,000 the intensity of sunlight, so is not strong enough to enable plants to photosynthesise. At night, plants survive by using the oxygen left over from the daylight photosynthesis or takes the oxygen from the air surrounding it.

Perhaps this is not the full story, or even the correct one...Colleen...anyone.

[Sarah Elizabeth]

Apparently we would need a universe with a Density of ten million times more stars to produce reflectivity from planets or stars to allow a bit of photosynthesis. Even this  is only theoretical however.

[Terry Whitaker]

I used to work on Antarctic phytoplankton and many Antarctic aquatic plants do photosynthesize at very low light intensities. Often however the rate of carbon loss by respiration is greater than carbon fixed by photosynthesis. Paradoxically at very low temperatures they can show positive carbon fixation because respiration is depressed more by reducing temperature than photosynthesis.

[Fred]

This is interesting when considering human sensitivity to moonlight and the sudden leap and subsequent drop in intensity of light reaching the earth (on clear nights!) a day either side of the fullmoon - about 30%. Apparently it's due to lunar dust acting like Scotchlite reflective tape in hi-viz vests. Those three days of 'lunar opposition effect' have been known (from only one source, I'm afraid. Hence this note!) to re-regulate irregular menstrual cycles in women. So, perhaps people 'photosynthesize' too in moonlight! Even if hormonal synthesis is simply triggered by this phenomenon.

[matty]

it's difficult for me to believe that any plant that is receiving direct moonlight- wether waxing, waning, or full- doesn't feel it just because photosynthesis isn't happening.