Emerged: Seeds of thale cress on lunar substrate in the University of Florida laboratory
Photo: Tyler Jones / UF / IFAS / REUTERS
This study could go down in the history of space travel: For the first time, researchers have grown plants on real lunar substrate.
They systematically examined whether agriculture would be possible on the celestial body in the future.
The result: Plants could in principle grow on "Monderde", reports the team from the University of Florida in Gainesville in the journal "Communications Biology".
However, their growth was stunted and the plants were showing severe signs of stress.
For Urs Mall from the Max Planck Institute for Solar System Research in Göttingen, the study contains “undoubtedly interesting observations”.
However, there are still many unanswered questions, says the moon expert, who was not involved in the study.
The cultivation of plants on the moon would be of particular interest for NASA's Artemis program: the US space agency wants to bring people to the moon again for the first time since the Apollo 17 mission in 1972 and set up a base there - if possible by the end of the decade .
Moon as a base for larger missions
In this project, plants could not only simplify the diet of the crew, but also produce oxygen.
"You want a closed cycle where everything is recycled," explains Mall, referring, among other things, to the carbon dioxide (CO₂) emitted by humans.
»Plants would play an important role in this cycle.«
"Artemis requires a better understanding of how plants grow in space," explains co-author Rob Ferl.
»For future, larger space missions, we could use the moon as a hub or launch pad.
So it makes sense to use the soil that is already there to grow plants.«
The researchers are now checking whether this would even be possible on the loose material on the moon.
This so-called regolith was formed by the intensive bombardment of the moon with meteorites.
Over the millions of years, the impacts shattered rock and crushed it into a kind of sand that sometimes covered the surface of the Earth's satellite several meters high.
The key difference to terrestrial soils: "On Earth, soils are biologically influenced," says Mall, referring to plants, animals and microorganisms.
"That's missing on the moon."
Twelve germs on twelve grams of soil
For the study, the team had only about 12 grams of lunar material that Apollo 11, 12, and 17 had brought back to Earth from their respective landing sites.
The material was sieved to a grain size of less than one millimeter, provided with rock wool and an aqueous nutrient solution and placed in mini containers at 0.9 grams each.
The researchers then placed seeds of the thale cress (Arabidopsis thaliana) on the substrate.
This plant, which is also widespread in Germany, is used in biology as a model organism, partly because its genome has been completely sequenced.
First, all twelve seeds germinated.
"We didn't predict that," says lead author Anna-Lisa Paul.
“It showed us that lunar soils do not disrupt the hormones and signals involved in plant germination.” However, problems quickly became apparent that did not occur with the control plants in terrestrial substrate similar to the lunar material: the plants grew more slowly, remained smaller, discolored themselves and varied greatly overall.
Older material is less suitable
The researchers interpret all of this as a sign of stress.
Further analysis revealed that gene activity was similar to that of plants exposed to unfavorable factors such as salt, metals or oxidative stress.
"From this we deduce that the plants found the lunar soil conditions to be stressful," says Paul.
However, the team registered noticeable differences between the various lunar substrates: Plants thrived the worst on the material that Apollo 11 had brought to Earth.
Unlike the Apollo 12 and Apollo 17 sites, the lunar regolith at this landing site is older and has therefore been exposed to cosmic rays and the solar wind longer.
These streams of charged particles constantly rain down on the lunar material and enrich it with hydrogen and helium ions in particular.
Overall, according to the research group, plants can grow on "moon soil", but this is basically not a good growth environment.
"The data suggest that older regolith provides an inferior substrate for plant growth than younger regolith," the team writes.
The plants thrived best on the material brought back by Apollo 17.
The study leaves many questions unanswered, says Mall.
In particular, it remains unclear which components of the lunar material were responsible for the problems affecting the plants.
"Many factors can play a role here." The authors themselves also point out these weaknesses: Before lunar regolith can be used as a local resource for plant cultivation, this material has to be better characterized and optimized.