Growing Plants in Lunar Regolith
Matthew Eagling
Advanced Concepts Team, ESA
Previous research has shown that it is possible to cultivate terrestrial plants within both lunar and Martian regolith simulants these previous studies have primarily focused on attempting to cultivate conventional crop plants such as tomatoes, potatoes, and berries. However, these experiments also found that these plants are typically stunted and poorly developed and any crops produced are small and poor-quality compared to specimens grown in terrestrial soils.
Recently (2022) a paper was published by the University of Florida which demonstrated that specimens of Arabidopsis thaliana (a small and rapidly growing plant, commonly used for laboratory investigations) were able to germinate and grow in real samples of lunar regolith, retrieved between 1969 1972 by the Apollo 11, 12 and 17 missions. These specimens demonstrated poor growth and development even relative to comparison specimens grown in lunar regolith simulant samples. This study confirmed the observations that lunar regolith, in its natural state, is not a benign substrate and the growth of crops in such an environment would be highly problematic.
Though often termed Lunar Soil, the lunar regolith is in fact not equivalent, or even close in composition to a terrestrial soil. Soils are mixtures of organic matter, minerals, gases, liquids, and microorganisms that are, together, able to support life [3]. New soils are created from freshly created or exposed rock (the soil parent material) via a combination of biological, physical, and chemical processes, which enable soils to evolve throughout their lifespan. Many of these processes are absent or heavily suppressed in the lunar environment leading to a lack of available essential plant nutrients, poor physical soil properties and a lack of beneficial biological activity, all of which contribute to an unfavorable environment for growth.
However, previous investigations appear to have overlooked two key facts: (1) On Earth, not all areas where plant growth is taking place are suitable for growing crop plants and yet are able to support select groups of organisms which have evolved to take advantage of conventionally hostile conditions. (2) Soil formation is a process that has, for the vast majority of the life span of the Earth, been taking place purely as a result of natural processes, without human interference and as such, many species of soil microorganisms, algae, lichen and higher plants are able to induce compositional and physical changes within a substrate which promote its transition to a material that can be recognized as a soil.
By identifying terrestrial species both able to colonise environments with similar compositions to lunar regolith and which have previously been documented as possessing properties that make them useful for land reclamation, environmental remediation, improving soil health for agriculture etc., we can identify candidates with the potential to induce these environmental improvements within lunar regolith and begin the conversion of lunar material into a more suitable substrate for the growth of useful plant species.