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The short version of my question is this:

It's some time in the future. I go into my back garden and focus my telescope on the Moon. The surface is virtually covered with giant greenhouses, growing food to support the cities that have sprung up there. The question is: what plants are they growing in those greenhouses?

Factors such as temperature, water, soil quality etc. can be controlled easily enough if you already have the ability to build sealed greenhouses in a vacuum. There are also a number of experiments on growing food in closed systems where air and water are recycled (the Biosphere 2 project being the best known). The low gravity can't be controlled, but there have been a number of experiments on plant growth in microgravity conducted on the international space station, so growing plants in Lunar gravity should be possible. There have also been some interesting results from growing plants in an Earth-based approximation to Lunar soil.

However, another important issue is the length of the Lunar day, which is 28 Earth days long, meaning that the Sun shines continuously for two Earth weeks, followed by two weeks of total darkness. I'm interested in what's known about how plants could adapt to this, but I haven't been able to find any research papers on the subject. Of course it would be possible to simulate an Earth day using artificial lighting, but the energy costs of doing this on a large scale would be rather high, so for economic reasons future Lunar farmers would likely want to keep it to a minimum.

So my first question is, has any research been done on the effect of extreme changes in day length on plant growth?

Secondly, is there any type of food plant that would be particularly likely to cope with such an environment (perhaps with some suitable genetic modifications)? For example, would normal crop plants such as cereals be able to build up enough sugar reserves in two weeks to survive the next two weeks in total darkness? If not, is there another type of plant that's more likely to be able to adapt to this? Or as an alternative strategy, is there any crop that grows fast enough that its shoots could be harvested after only two weeks of continuous sunlight? (Some individuals would have to be grown to maturity under artificial light in order to produce seeds, of course.)

Finally, I'd be grateful for pointers towards research on any other issues that I might have missed that are relevant to the problem of large-scale Lunar agriculture.

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this question is quite long, perhaps you could make it clearer what you are trying to ask –  rg255 Nov 5 '13 at 11:43
@GriffinEvo are long questions considered bad here? If so that makes me sad. I think I've set out quite clearly what I'm asking in the final three paragraphs - could you please be more specific about what you found unclear? –  Nathaniel Nov 5 '13 at 16:22
There is no limit on length, I just feel that the key points you are trying to get to get a little lost and could be made to be more obvious, questions that are long or difficult to get to key point of are less likely to get good answers. So don't be sad :) –  rg255 Nov 5 '13 at 16:41
I suggest you rephrase your question to remove the reference to the moon. The obvious answer is that artificial light can be used and controlled so there is no reason why growing crops on the moon would be affected by its day/night cycle. Consider that if we have bases on the moon, we will already have lighting and the expense will be negligible compared to everything else necessary to make that possible. The question you are asking is how plants can/could adapt to different day/night cycles and it is a very interesting question but mentioning the moon distracts from it and confuses the issue. –  terdon Nov 6 '13 at 15:16
I agree with @terdon and think that the Q should be rephrased. Both "how plants cope with extreme day/night cycles" and "what plants that might be suitable for lunar greenhouses" are interesting questions, but at the moment your question is a bit unclear. –  fileunderwater Nov 7 '13 at 13:48

1 Answer 1

Plants are adapted to the conditions we have here on earth, therefore, for them to grow on the moon we would have to recreate the conditions found on earth (or at least find conditions that we can create and they can grow in). To do this we would need to replicate climate (temperature, air pressure, humidty etc.), provide (sun)light at the necessary intervals and intensity, provide water, air, and nutrients of the right composition, intervals and intensity. That is a simplified version...

In reality there is great variation in how plants require these things. Some cope with long dark periods better than others, some cope with drought better than others, some cope with chemical variation in the soil better than others so answering this question is hard. But generally growing plants on the moon will require the ability to recreate (to some degree depending on the sensitivity of the plant) the conditions a plant has evolved under on earth.

Thus to answer your questions:

Length of day can have strong effects on growth patterns, two weeks of darkness is likely to be a major upset for plants! Just transplanting plants of the same species from different latitudes can affect the growth patterns because of changes in length of day. Try putting some plants in darkness for two weeks and see what happens.

Plants all vary in their ability to meet the requirements of space growth. There will only be a short list of plants that could with "small" modifications to the moon's environment, the more we adapt (adding artificial light, watering, adding nutrients etc) the longer that list would become - the limitation is in our ability to adapt the moon.

See above for reasons why plants might struggle. Oh and we would need to consider the effects of reduced gravity too...

Here's a little something from nasa about how plants are used in space vehicles. And another on light and gravity.

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Thanks, but I did mention in the question that I'm aware of research on most of these issues. I'm asking if there is any research specifically on the day length issue, and also about which specific types of plant are most likely to be able to adapt. –  Nathaniel Nov 5 '13 at 16:30
@Nathaniel I think if we get to the point where we can realistically inhabit the moon and modify it to grow some plants, then we should be able to get it to the point where most can grow. Whether it's wheat, corn, or oak trees, there will have to be some significant modifications made by us to the moon before we can grow any. Once we can grow one then small tweaks to the system will be needed to grow the others. Feels like its more how we could adapt the moon than how the plants can adapt. It's likely small simple things would be easiest for us to grow but crop plants would be most necessary –  rg255 Nov 5 '13 at 16:51
Sure - my thinking is that factors like water, soil quality, atmosphere etc. are easy enough to control if you already have the technology to build sealed greenhouses in a vacuum. Gravity can't be controlled at all, but if we can grow plants on the ISS then it should work on the Moon. That leaves the day length, which can only be changed using artificial lighting, which will need an expensive source of energy. So my guess is that the choice of which crop to grow would be mostly determined by its ability to cope with weeks of darkness. –  Nathaniel Nov 6 '13 at 7:30
@Nathaniel I can't find any research testing such long periods of light deprevation but my gut feeling is telling me not much would do well. These shade tolerant plants still need a few hours of sunlight per day motherearthnews.com/organic-gardening/… –  rg255 Nov 6 '13 at 9:21
something like this might work... nytimes.com/1993/01/12/science/… –  rg255 Nov 6 '13 at 9:23

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