Is the lunar surface material suitable for growing plants? Researchers have now investigated this question for the first time with a growth test using sample material from the Apollo missions. In principle, plants can therefore thrive on the so-called lunar regolith – but it apparently does not form a good substrate: the test plants grew comparatively poorly and showed signs of stress. The scientists say that the extent to which the lunar material is suitable for growing plants in the greenhouses of future lunar stations must therefore be examined more closely.
The step to the moon was made more than 50 years ago – now man is planning to gain a permanent foothold there: In the coming decades, stations are to be built on the moon’s surface, which could enable a permanent presence on the celestial body closest to us. The so-called Artemis program of NASA is dedicated to this goal. As part of this, scientists are also investigating the extent to which it is possible to grow plants on the moon for food and oxygen supply. “It makes sense that we would want to use the soil that’s already there to grow crops,” says Rob Ferl of the University of Florida at Gainesville.
So far, however, it has remained unclear how plants react to the moon’s surface material, which differs significantly from terrestrial substrates. It has special mineral combinations, is extremely fine-grained and is also characterized by tiny glass particles that come from impacts on the moon. In addition, certain components are shaped by the material’s long exposure to radiation in space. For this reason, lunar regolith cannot be reproduced in detail to clarify the extent to which plants can grow on the extraterrestrial substrate.
Sample material for a tiny “moon garden”
The original material that astronauts brought back from the Apollo missions was previously considered too valuable to be used for growth tests. Plants have therefore only been pollinated with it to show that it does not cause biological damage, at least in this way. But now NASA has finally provided Ferl and his colleagues with sample material for use as a plant substrate. However, this was of course not a sack like from the garden center: the scientists only had twelve grams of lunar soil – a few teaspoons – available for their experiments. The material came from the Apollo 11, 12 and 17 missions and was collected at various points on the lunar surface.
So minimalism was the order of the day in the researchers’ experiments. To create their tiny “moon garden” in the lab, they used thimble-sized wells in plastic plates commonly used for cell culture. The indentations functioned as plant pots: they were each filled with about one gram of moon soil and “cast” with a nutrient solution. The scientists then placed a seed of thale cress (Arabidopsis thaliana) on the substrate. This is the best-studied plant in the world – it has served as a model for scientists for many years, and its characteristics and genetic responses are known in detail. The comparison substrate used in the study was, among other things, a material that has at least fundamentally similar characteristics to the lunar soil.
As the researchers emphasize, it was not even clear whether the seeds would germinate at all due to the special characteristics of the lunar soil. But as it turned out, it worked. “It first became clear that the lunar soils do not interrupt the hormones and signals involved in plant germination,” explains lead author Anna-Lisa Paul from the University of Florida in Gainesville. In the course of further development, however, differences between the plants in the lunar soil and the control groups became apparent: many remained smaller, grew more slowly and formed stunted roots in the “alien substrate”. Some also produced reddish-black pigments—traits typically indicative of plant stress.
Growth yes, but…
The plants can therefore survive, but the chemical and structural properties of the lunar soil obviously pose a challenge for them, the researchers explain. This was also reflected in the genetic activity, as transcriptome analyzes showed. “It became clear that the plants activated the typical tools to cope with stress from salts and metal compounds or oxidative stress. This confirms that they find the lunar soil problematic,” says Paul. Specifically, the researchers suspect that features of the lunar soil caused by cosmic rays and solar wind, as well as certain iron particles, cause problems for the plants.
The results also suggest that where the lunar soil came from matters. Because the plants with the most stress symptoms were those grown in the Apollo 11 samples. This material is referred to as “mature”: For geological reasons, it was apparently exposed to hard cosmic rays for longer than the other samples, which shaped its characteristics.
As the researchers conclude, there is now a need for further research to better explore the potential for growing plants in lunar soil. Perhaps there are ways to mitigate stress responses enough to allow plants to grow on lunar soil without compromising their health. Another aspect is that the cultivation itself could change the substrate. At the moment, the researchers are pleased that they have successfully completed the first steps towards plant cultivation on the moon. “First of all, we wanted to answer the question of whether plants grow in lunar soil at all. We can now answer that in the affirmative,” says Ferl.
Source: University of Florida, Article: Communications Biology, doi:10.1038/s42003-022-03334-8