How well do plants grow in moon dust? – First lunar regolith samples tested from the Apollo missions

Mixed results: For the first time, terrestrial plants grew on real lunar material — samples of lunar dust from the Apollo missions. The cotyledons were actually grown from seeds on a regolith that had been fertilized with a nutrient solution. However, the plants were small in size, with discolored leaves, and their gene activity also indicated massive stress reactions. Thus, growing plants on lunar soil is in principle possible, but difficult.

Astronauts will be in the near future back to the moon And maybe there permanently lunar stations erect. However, one of the prerequisites for such a satellite colonization of the Earth is sufficient resources – water, oxygen and energy must be obtained on site. The same applies to the food supply, especially with plants.

Plants for future lunar colonies

Scientists have long been testing how vegetables and their partners can be grown under the conditions of the Moon and Mars hydroponic greenhouses Among other things in the Antarctic, but also with Analogues of Regolith. It consists of volcanic sand from Hawaii, whose sharp grains and mineral texture are similar to those found in the Earth’s interior on the Moon. Indeed, tomatoes, lettuce, and their mates grew relatively well over their counterparts – but does this also apply to true lunar regolith?

Anna Lisa Ball at the University of Florida in Gainesville and her colleagues have now tested this: They were the first research team that got the chance to do so. real lunar material From the Apollo missions basin. Moon samples brought to Earth by NASA astronauts about 50 years ago are still very valuable for planetary research, and therefore are only available for a select few tests.

First test using Apollo moondust

But after eleven years of waiting, Paul and her team finally got lucky: They received twelve grams of moon dust for their farming experiments. The samples came from three different lunar missions: The regoliths from Apollo 11 and 12 have been exposed to the harsh radiation of the lunar surface for some time, and thus “mature” chemically and physically, the team explains. On the other hand, the Apollo 17 samples contained “immature” lunar dust from weather-protected site samples in space.

For their tests, the researchers had to use the valuable substance in moderation: they used small indentations in a plastic tray typically 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 the seeds of cress (Arabidopsis thaliana) – an experimental plant that has been genetically proven and well studied. A rich analogue, JSC-1A, developed by NASA, served as a control.

Germination works, growth only to a limited extent

It turned out that all the seeds germinated 48 to 60 hours after planting and that the lunar seedlings developed normal stems and plants. “We were surprised, we didn’t expect it,” Paul says. “This shows us that lunar soil does not interrupt the signals and hormones of plant germination.”

After only a few days, the first differences became apparent: “Compared to the analogue plants JSC-1A, lunar plants took longer to unfold their leaves, had smaller rosettes, some were very stunted and had intense pigmentation – a typical indicator of plant stress, ” Researchers report. Instead of the usual green, the plants growing on the lunar regolith were tinged with reddish-brown hues.

Test plants on the Apollo 11 samples were the hardest hit, but growth was slightly better on lunar materials less weathered than on the Apollo 17 samples, the team reported.

Marked response to genetic stress

To learn more about the causes of poor growth, Paul and her colleagues analyzed the genetic activity of test plants. Here, too, there were clear differences in the isotope of the regolith: in plants growing on lunar material, hundreds of genes typical of high stress loads were active. The researchers reported that “71 percent of these genes are associated with exposure to salts, metals, and highly reactive oxygen compounds.”

This gene stress response also showed a graded response to ‘mature’ lunar regolith differently: plants on the Apollo 11 substrate activated 465 stress-related genes, while Apollo 12 plants on less weathered lunar dust activated ES 265 and Apollo-17. 113 stress genes. “This indicates that the plant’s response also depends on the type of regolith,” Ball and colleagues write.

Cultivation of lunar crops – possible but difficult

In general, the results indicate that plants can, in principle, grow on lunar dust if it is enriched with a nutrient solution. “However, lunar regolith is not a plant-friendly growth substrate,” the team says. Even plants that are still reasonably well developed show clear signs of high levels of stress. Whether this can be compensated for and how further research needs to be done now.

Another consequence: if you build lunar greenhouses, you should use the “immature” regolith as much as possible and with little exposure to radiation. Because the chemical-physical changes in which the material accumulates on the lunar surface over time appears to be particularly unpalatable to terrestrial plants.

However, it is still not clear whether plants can withstand the high levels of radiation on the moon’s surface. China’s Chang’e 4 lunar lander did it in 2019 successful germination that were detected by the test plants in a germination container brought in. Earth Growth Tests under increased radiation showed, however, that this also leads to growth arrest and plant stress reactions. (Communication Biology, 2022; doi: 10.1038/s42003-022-03334-8)

Source: University of Florida

May 16 2022

– Nadia Podebrigar