Mixed Results: For the first time, terrestrial plants have grown on real lunar material — lunar dust samples from the Apollo missions. Plantlets actually developed from the seeds on the regolith enriched with nutrient solution. However, the plants were puny, had discolored leaves and their gene activity also indicated massive stress reactions. Plant cultivation on lunar subsoil is therefore possible in principle, but difficult.
Astronauts will return to the moon in the near future and may even set up permanent lunar stations there. However, a prerequisite for such a colonization of the Earth’s satellite are sufficient resources – water, oxygen and energy must be obtained on site. The same applies to the food supply, especially with plants.
Plants for the lunar colonies of the future
Scientists have long been testing how vegetables and co. can be grown under lunar and Martian conditions using hydroponic greenhouses in the Antarctic, among other places, but also using regolith analogues. These consist of volcanic sand from Hawaii, whose sharp-edged grains and mineral texture are similar to those of the lunar subsoil. In fact, tomatoes, lettuce and co grew relatively well on such analogues – but would this also apply to real lunar regolith?
Anna-Lisa Paul from the University of Florida in Gainesville and her colleagues have now tested this: They were the first research team ever to have the opportunity to use real moon material from the Apollo missions fund. The moon samples brought to earth by NASA astronauts around 50 years ago are still extremely valuable for planetary research and are therefore only made available for a few selected tests.
First test with Apollo moondust
But after eleven years of waiting, Paul and her team finally got lucky: they received twelve grams of moon dust for their planting experiments. The samples came from three different lunar missions: The regolith from Apollo 11 and 12 had been exposed to the harsh radiation of the lunar surface for some time and was therefore chemically and physically “ripened”, as the team explains. The Apollo 17 samples, on the other hand, contained “immature” lunar dust from sample sites protected from space weathering.
For their tests, the researchers had to use the valuable material sparingly: They used the tiny indentations in a plastic tray normally used for cell culture tests as “flower pots”. They filled one gram of regolith into each of these depressions, moistened it with a nutrient solution and added thale cress (Arabidopsis thaliana) seeds – a proven and genetically well-studied experimental plant. The JSC-1A regolith analogue developed by NASA served as a control.
Germination works, growth only to a limited extent
It turned out that all seeds germinated between 48 and 60 hours after planting and the lunar seedlings developed normal stems and cotyledons. “We were surprised, we didn’t expect that,” says Paul. “This shows us that the lunar soils do not interrupt the signals and hormones of plant germination.” In the further course, all plants grew and developed roots and more leaves.
After just a few days, however, the first differences became apparent: “Compared to the JSC-1A analogue, the lunar plants took longer to unfold their leaves, had smaller leaf rosettes and some were very stunted and heavily pigmented – this is a typical indicator for plant plants stress,” the researchers report. Instead of the usual green, the plants growing on lunar regolith were tinged with reddish and brownish hues.
The test plants on the Apolo 11 samples were most affected, but growth was slightly better on the less weathered lunar material from the Apollo 17 samples, the team reports.
Marked genetic stress response
To find out more about the causes of the impaired growth, Paul and her colleagues analyzed the gene activity of the test plantlets. Here, too, there were clear differences to the regolith analogue: in the plants growing on lunar material, hundreds of genes that are typical for high stress loads were active. “71 percent of these genes are linked to exposure to salts, metals and highly reactive oxygen compounds,” the researchers report.
This genetic stress response also showed a graded response to the differently “mature” lunar regoliths: the plants on the Apollo 11 substrate had activated 465 stress-associated genes, while the Apollo 12 plants on the slightly less weathered lunar dust had activated them es 265 and Apollo-17 113 stress genes. “This suggests that the plant response also depends on the type of regolith,” write Paul and her colleagues.
Lunar crop cultivation – possible, but difficult
Overall, the results suggest that plants can, in principle, grow on lunar dust if it is enriched with nutrient solution. “However, the lunar regolith is not a very plant-friendly growth substrate,” the team says. Even the plants that are still developing reasonably well show clear signs of high stress levels. Whether and how this could possibly be compensated for must now be further researched.
Another finding: If you set up lunar greenhouses, you should use regolith that is as “immature” as possible and has little exposure to radiation. Because the chemical-physical changes that the material accumulates on the moon’s surface over time seem to be particularly unpalatable for terrestrial plants.
However, it remains unclear whether plants could withstand the high radiation exposure on the moon’s surface at all. In 2019, the Chinese lunar lander Chang’e 4 demonstrated the successful germination of test plants in a germination container they had brought with them. However, terrestrial growth tests under increased radiation have shown that this also leads to stunted growth and plant stress reactions. (Communications Biology, 2022; doi: 10.1038/s42003-022-03334-8)
Source: University of Florida
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