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.