But the experiments also reveal how stressful it is for plants to grow in lunar regolith, or soil, which is very different from natural habitats on Earth.
Different types of plants, including food crops, flew on the Space Shuttle and the International Space Station. Plant samples have even been used to prove that lunar samples are not harmful to life on Earth.
“The plants helped establish that soil samples brought back from the moon did not harbor pathogens or other unknown compounds that could harm life on Earth, but these plants were only dusted with lunar regolith. and were never actually cultivated there,” said study co-author Anna. -Lisa Paul, research professor of horticultural sciences at the University of Florida’s Institute of Food and Agricultural Sciences.
Paul and study co-author Rob Ferl, a distinguished professor of horticultural sciences at the UF Institute of Food and Agricultural Sciences, wanted to dig deeper and see if the seeds would grow in lunar soil.
“For future, longer space missions, we could use the Moon as a hub or launch pad,” Ferl said in a statement. “So what happens when you grow plants in lunar soil, something that’s totally outside of a plant’s evolutionary experience? What would plants do in a lunar greenhouse? Could we have lunar farmers?”
It’s a long-running experiment – 15 years have passed since the researchers made their first proposal and request for lunar samples. The request was accepted 18 months ago.
The research team requested 4 grams of lunar material collected during the Apollo 17 mission from NASA. Ryan Zeigler, NASA’s Apollo Sample Curator, saw the scientific value in providing more of the different Apollo missions. He sent them a total of 12 grams (2.7 teaspoons) of lunar samples collected during the Apollo 11, 12 and 17 missions.
“It’s made a big difference in allowing us to dig deeper into the science and effects of lunar regolith on plants than we otherwise could have,” Paul said.
The researchers used thimble-sized wells as pots. Generally, these plastic trays are used for cell culture.
Scientists filled each well with one gram of lunar soil, added nutrients and water, and poked in some seeds of Arabidopsis thaliana, or watercress, a small flowering plant native to Eurasia and Africa.
Thale watercress is an attractive plant specimen for researchers because it is well studied and its genetic code has been mapped, which allowed researchers to study how foreign soil affected gene expression in the plant. And the plant has already traveled to space aboard the shuttle and the space station, providing the team with spatial data to use for comparison.
Arabidopsis seeds were also planted in a synthetic substance that simulates lunar soil, as well as volcanic ash and other substrates from extreme environments.
To the researchers’ surprise, almost all of the seeds planted in the dark lunar soil actually germinated and began to grow.
“We didn’t plan for this,” Paul said. “It told us that lunar soils weren’t disrupting the hormones and signals involved in plant germination.”
The Arabidopsis sprouts, however, showed signs of a struggle as they adapted to the lunar soil.
The seedlings were smaller, grew more slowly, and varied in size compared to plants grown in terrestrial soils. The roots were stunted. And the plants took longer to develop enlarged leaves than Arabidopsis plants grown in volcanic ash. Some of the lunar soil plants showed reddish black pigments in their leaves, an outward sign of stress.
Genetically, three of the smallest and darkest plants expressed more than 1,000 genes largely related to stress.
“At the genetic level, plants were releasing the tools typically used to deal with stressors, such as salt and metals or oxidative stress, so we can infer that plants perceive the lunar soil environment as stressful.” , said Paul.
“Ultimately, we’d like to use gene expression data to help determine how we can improve stress responses to the level where plants – especially crops – are able to grow in lunar soil with very little stress. impact on their health.
The Arabidopsis plants that suffered the most were grown in mature lunar soil and turned purple in response to oxidative stress. These soils collected during the Apollo 11 mission were more exposed to the harsh space environment, and the plants grown in the Apollo 12 and 17 samples seemed to fare better.
The lunar surface, regularly bombarded by cosmic rays and the solar wind, also includes particles of iron and tiny fragments of glass. All of these could harm plant growth.
“Even plants that looked healthy had a hard time staying healthy,” Paul said. “They grew up in lunar regolith, but they had to deal with it on a metabolic level in order to maintain that kind of health.”
Researchers want to conduct follow-up studies to understand how growing plants in the lunar environment might actually alter the moon’s soil.
“The Moon is a very, very dry place,” said study co-author Stephen Elardo, assistant professor of geology at UF. “How will lunar soil minerals react to plant growth, with the addition of water and nutrients? Will the addition of water make the mineralogy more hospitable to plants?”
On the moon, these plants could pull resources from the lunar soil, such as metallic iron, and make them available in useful forms.
Further research could also help researchers determine the most efficient way to grow plants in lunar soil and avoid stressors identified during the study. And the team wanted to come to a clear understanding of the nutritional value of these plants – and whether this is affected by soil.
Although Thale watercress is edible, it is not tasty or considered a food crop. But it’s in the same plant family as broccoli, kale, turnips, and cauliflower.
Sharmila Bhattacharya, chief scientist for astrobionics at NASA, found the discovery of plant growth “quite exciting” and said the study presents many follow-up opportunities for scientists. Bhattacharya did not participate in this study.
“We need to figure out how to make plants grow even better in this regolith substrate,” Bhattacharya wrote in an email. “For example, do we need to add other compounds to help the plants move forward, and if so, what are they? Are there other plants that may adapt better to these regolith substrates, and if so, what traits make them more hardy to these substrates. environments?
“That’s what’s so exciting about science; each new discovery leads to more unique and transformative results down the road, which we can then use to help improve the sustainability of our future space exploration missions!”
Scientists see their experiment as a positive outcome for what may be possible as humans push the boundaries of space exploration.
“It’s amazing that the plant is still growing in this harsh environment,” Elardo said. “He’s stressed, but he’s not dying.”
“When humans move as civilizations to stay somewhere, we always take our agriculture with us,” Ferl said. “The idea of bringing lunar soil into a lunar greenhouse makes exploration dream.”