What do you need to make your garden grow? In addition to plenty of sunshine alternating with gentle rains – and busy bees and butterflies to pollinate the plants – you need good, rich soil to provide essential minerals. But imagine that you have no rich soil, no rain, no bees and butterflies. And sunlight was either too strong and direct or absent – causing freezing temperatures.
Could plants grow in such an environment – and if so, which ones? This is the question colonists on the Moon (and Mars) would have to resolve if (or when) human exploration of our planetary neighbors goes ahead. 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 lunar regolith (soil) samples brought back from three different places on the Moon by the Apollo astronauts.
This is not the first time that attempts have been made to grow plants in the lunar regolith, but it is the first to demonstrate why they do not thrive.
Lunar regolith is very different from terrestrial soils. For starters, it contains no organic matter (worms, bacteria, decaying plant matter) that is characteristic of Earth’s soil. Nor does it have an inherent water content.
But it is made up of the same minerals as terrestrial soils, so assuming the lack of water, sunlight and air is ameliorated by growing plants within a lunar habitat, regolith could have the potential to grow plants.
Research has shown that this actually happens. seeds of A. thaliana germinated at the same rate in Apollo material as they did in terrestrial soil. But while plants in terrestrial soil began to develop rootstocks and produce leaves, Apollo seedlings stunted and had poor root growth.
The main objective of the research was to examine plants at the genetic level. This allowed the scientists to recognize which specific environmental factors evoked the strongest genetic responses to stress. They found that most of the stress reaction in all of the Apollo seedlings came from highly reactive salts, metal and oxygen (the latter two not common in terrestrial soil) in the lunar samples.
The three Apollo samples were affected to different degrees, with the Apollo 11 samples being the slowest to grow. Given that the chemical and mineralogical composition of the three Apollo soils were quite similar to each other and to the terrestrial sample, the researchers suspected that nutrients were not the only force at play.
The terrestrial ground, called JSC-1A, was not a regular ground. 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 “glass agglutinates” – small mineral fragments mixed with molten glass – that are abundant in lunar regolith.
Scientists recognized the clumps as one of the potential reasons for the lack of growth of seedlings 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 known as “moon gardening”. This is how the regolith changes, through the bombardment of the Moon’s surface by cosmic radiation, solar wind and tiny meteorites, also known as space weathering.
As there is no atmosphere to slow down the tiny meteorites that hit the surface, they impact at high speed, causing melting and then extinction (rapid cooling) at the impact site.
Gradually, small aggregates of minerals build up, held together by the glass. They also contain small particles of metallic iron (nanophase iron) formed by the space weathering process.
It is this iron that is the biggest difference between the vitreous agglutinates in the Apollo samples and the naturally occurring volcanic glass in the terrestrial sample. This was also the most likely cause of the metal-associated stress recognized in the plant’s genetic profiles.
Thus, the presence of clumps in lunar substrates caused Apollo seedlings to suffer compared to seedlings grown in JSC-1A, particularly Apollo-11 seedlings. The abundance of clumps in a lunar regolith sample depends on how long the material has been exposed on the surface, which is called 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 (below-surface) soils occur around fresh craters and on steep crater slopes.
The three Apollo samples had different maturities, with Apollo 11 material being the most mature. It contained more nanophase iron and exhibited the stress markers associated with metals higher 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 demonstrates that plants can be grown in lunar habitats using regolith as a resource. But that the location of the habitat must be guided by the maturity of the soil.
And one last thought: it occurred to me that the findings might also apply to some of the impoverished regions of our world. I don’t want to repeat the old argument of “Why spend all that money on space research when it could be better spent on schools and hospitals?” That would be a subject for another article.
But are there technological developments emerging from this research that could 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 a great achievement if making plants grow on the Moon were instrumental in helping gardens grow 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.