What do you need to grow your garden? In addition to plenty of sunshine alternating with gentle showers of rain, and busy bees and butterflies to pollinate the plants, you need good, rich soil to provide essential minerals. But imagine that you have no fertile soil, no downpours, no bees and no butterflies. And the sunlight was either too strong and direct or absent, leading to sub-zero temperatures.
Could plants grow in such an environment, and if so, which ones? This is the question that colonists on the Moon (and Mars) would have to address if (or when) human exploration of our planetary neighbors continues. Now a new study, published in Communications Biology, has begun to provide answers.
The researchers behind the study cultivated the fast-growing plant. Arabidopsis thaliana in samples of lunar regolith (soil) brought back from three different places on the Moon by the Apollo astronauts.
However, this is not the first time that plants have been tried to grow in the lunar regolith, but it is the first time that it has been shown why they do not thrive.
Lunar regolith is very different from terrestrial soils. For starters, it doesn’t contain the organic matter (worms, bacteria, decaying plant matter) that is characteristic of Earth’s soil. It also has no inherent water content.
But it is composed of the same minerals as terrestrial soils, so assuming the lack of water, sunlight, and air is alleviated by growing plants within a lunar habitat, then regolith could have the potential to grow plants.
The investigation showed that this is indeed the case. Seeds of a. thaliana they germinated at the same rate in the Apollo material as they did in terrestrial soil. But while the plants in the terrestrial soil developed rootstocks and put out leaves, the Apollo seedlings were stunted and had poor root growth.
The main objective of the research was to examine the plants at the genetic level. This allowed scientists to recognize which specific environmental factors triggered the strongest genetic responses to stress. They found that most of the stress reaction in all of the Apollo seedlings came from salts, metals, and oxygen that is highly reactive (the latter two are not common in terrestrial soil) in the lunar samples.
The three Apollo samples were affected to different degrees, with the Apollo 11 samples growing the slowest. Since the chemical and mineralogical composition of the three Apollo soils was quite similar to each other and to the terrestrial sample, the researchers suspected that nutrients were not the only force at play.
The ground floor, called JSC-1A, was not a regular floor. It was a mixture of minerals prepared specifically to simulate the lunar surface and contained no organic matter.
The starting material was basalt, as in lunar regolith. The terrestrial version also contained natural volcanic glass as an analogue of the “vitreous agglutinates” (small mineral fragments mixed with molten glass) that abound in lunar regolith.
The scientists recognized clumping as one of the possible reasons for the lack of seedling growth in Apollo soil compared to terrestrial soil, and also for the difference in growth patterns between the three lunar samples.
Agglutinates are a common feature of the lunar surface. Ironically, they are formed by a process called “moon gardening.” This is how regolith changes, through the bombardment of the Moon’s surface by cosmic radiation, solar wind, and tiny meteorites, also known as space weathering.
Because there is no atmosphere to slow down the tiny meteorites hitting the surface, they impact at high speed, causing melting and then rapid cooling at the impact site.
Gradually, small aggregates of minerals, bound by glass, accumulate. They also contain tiny iron metal particles (nanophase iron) formed by the process of space weathering.
It is this iron that constitutes the major difference between the glassy agglutinates of the Apollo samples and the natural volcanic glass of the terrestrial sample. This was also the most likely cause of the metal-associated stress recognized in the plant genetic profiles.
So, the presence of agglutinates in the lunar substrates made the Apollo seedlings difficult compared to seedlings grown on JSC-1A, particularly those from Apollo-11. The abundance of agglutinates in a lunar regolith sample depends on how long the material has been exposed on the surface, which is known as the “maturity” of a lunar soil.
Very mature soils have been on the surface for a long time. They are found in places where the regolith has not been disturbed by more recent impact events that created craters, while immature (subsurface) soils are found around recent craters and on steep crater slopes.
The three Apollo samples had different maturities, with the Apollo 11 material being the most mature. It contained the highest amount of nanophase iron and exhibited the highest metal-associated stress markers in its genetic profile.
The importance of young soil
The study concludes that the more mature regolith was a less effective substrate for growing seedlings than the less mature soil. This is an important conclusion because it shows that plants could be grown in lunar habitats using regolith as a resource. But that habitat location should be guided by soil maturity.
And one final thought: It struck me that the findings could also apply to some of the impoverished regions of our world. I don’t want to rehearse the old argument of “Why spend all this money on space research when it could be better spent on schools and hospitals?” That would be the subject of another article.
But are there technological developments emerging from this research that might be applicable on Earth? Could what has been learned about stress-related genetic changes be used to develop more drought-resistant crops? Or plants that could tolerate higher levels of metals?
It would be quite an achievement if getting plants to grow on the Moon was instrumental in helping gardens get greener on Earth.
Article by Monica Grady, Professor of Planetary and Space Sciences, The Open University
This article is republished from The Conversation under a Creative Commons license. Read the original article.