Scientists have for the first time grown plants in lunar soil brought back to Earth by astronauts in the Apollo missions, a step towards producing food and oxygen on the Moon or during future space missions.
The researchers at the University of Florida (UF) in the US showed that plants can successfully sprout and grow in lunar soil.
Their study, published in the journal Communications Biology, also investigated how plants respond biologically to the Moon's soil, also known as lunar regolith, which is very different from soil found on Earth.
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This research comes as NASA's Artemis Program plans to return humans to the Moon.
"Artemis will require a better understanding of how to grow plants in space," said Rob Ferl, one of the study's authors and a professor at UF Institute of Food and Agricultural Sciences (UF/IFAS).
"For future, longer space missions, we may use the Moon as a hub or launching pad. It makes sense that we would want to use the soil that is already there to grow plants," Ferl said.
The researchers designed a simple experiment: plant seeds in lunar soil, add water, nutrients and light, and record the results.
They only had 12 grammes -- just a few teaspoons -- of lunar soil with which to do this experiment.
On loan from NASA, this soil was collected during the Apollo 11, 12 and 17 missions to the moon.
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The researchers applied three times over the course of 11 years for a chance to work with the lunar regolith.
To grow their tiny lunar garden, the researchers used thimble-sized wells in plastic plates normally used to culture cells. Each well functioned as a pot.
Once they filled each "pot" with approximately a gram of lunar soil, the scientists moistened the soil with a nutrient solution and added a few seeds from the Arabidopsis plant which is widely used in the research because its genetic code has been fully mapped.
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Growing Arabidopsis in the lunar soil allowed the researchers more insight into how the soil affected the plants, down to the level of gene expression.
As points of comparison, the researchers also planted Arabidopsis in JSC-1A, a terrestrial substance that mimics real lunar soil, as well as simulated Martian soils and terrestrial soils from extreme environments.
The plants grown in these non-lunar soils were the experiment's control group.
The researchers found that nearly all the seeds planted in the lunar soils were able to sprout.
"We were amazed. We did not predict that. That told us that the lunar soils did not interrupt the hormones and signals involved in plant germination," said Anna-Lisa Paul, one of the study's authors and a research professor of horticultural sciences in UF/IFAS.
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The researchers observed differences between the plants grown in lunar soil and the control group. For example, some of the plants grown in the lunar soils were smaller, grew more slowly or were more varied in size than their counterparts.
These were all physical signs that the plants were working to cope with the chemical and structural make-up of the Moon's soil, Paul explained.
This was further confirmed when the researchers analyzed the plants' gene expression patterns.
"At the genetic level, the plants were pulling out the tools typically used to cope with stressors, such as salt and metals or oxidative stress, so we can infer that the plants perceive the lunar soil environment as stressful," Paul said.
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"Ultimately, we would like to use the gene expression data to help address how we can ameliorate the stress responses to the level where plants -- particularly crops -- are able to grow in lunar soil with very little impact to their health," she said.
The researchers found that the plants with the most signs of stress were those grown in what lunar geologists call mature lunar soil.
These mature soils are those exposed to more cosmic wind, which alters their makeup. On the other hand, plants grown in comparatively less mature soils fared better, they added.