NASA revealed plans this week to set up a greenhouse on the surface of Mars by 2021.

As humans begin colonizing on the moon and Mars, they will need plants and greenhouses in order to survive. Greenhouses will help recycle the air, and will provide an important link in recycling for space colonists, according to a NASA press release.

"When you get to the idea of growing plants on the moon, or on Mars," said molecular biologist Rob Ferl, director of Space Agriculture Biotechnology Research and Education at the University of Florida, "then you have to consider the idea of growing plants in as reduced an atmospheric pressure as possible."

Some benefits of growing plants in a low-pressure environment includes reducing the weight of the air that will need to be carried to Mars.

Lunar greenhouses must also "hold up" in places where the atmospheric pressures is less than one percent of Earth-normal. Greenhouses will be easier to create and run if their interior pressure is also around one-sixteenth of Earth-normal, according to NASA.

Plants that have evolved on Earth might not have an easy time living on other planets however, even in greenhouses, according to Ferl.

"Remember, plants have no evolutionary preadaptation to hypobaria," said Ferl. 

Low pressure makes plants act like they're drying out, as there is no reason for them to have learned to interpret the biochemical signals induced by low pressure. 

Ferl's and his colleagues exposed young growing plants to pressures of one-tenth Earth normal for about twenty-four hours in recent experiments, supported by NASA's Office of Biological and Physical research.

Extra water is needed to replenish plants in such a low-pressure environment, since water is pulled out through the leaves very quickly.

Plants begin to act as if they are experiencing a drought when they're subjected to low pressures, according to Ferl.

Ferl added that once the plants' responses are understood, researchers can then adjust them.

"We can make biochemical alterations that change the level of hormones," said Ferl. "We can increase or decrease them to affect the plants' response to its environment."

Astronauts are hardly the only ones who will can benefit from this research.

Controlling air pressure in an Earth greenhouse or a storage bin may make it possible to influence certain plant behaviors.

"The exciting part of this is, we're beginning to understand what it will take to really use plants in our life support systems." said Ferl.

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