News release

From: Springer Nature

Unearthing the potential for life to survive in simulated extraterrestrial soil

Life’s capacity to survive in simulated lunar and Martian soils has been explored in two papers published in Scientific Reports. Treating simulated lunar soil with both symbiotic fungi and worm-produced compost can significantly improve the likelihood of reproduction for chickpea plants growing in the soil, indicates one study. A separate paper suggests that some microbes may be able to absorb enough water from the atmosphere to grow in simulated Martian soil at atmospheric humidity levels comparable to those on the planet.

Lunar soil — known technically as lunar regolith — does not support healthy plant growth, as it contains high concentrations of certain metals such as aluminium and zinc, does not allow water to filter through easily, and lacks the microbiome found in Earth soils. Previous research has investigated several ways to improve the fertility of lunar soil, although plants grown in these treated soils typically display various signs of stress, including stunted growth and leaf yellowing.

Jessica Atkin and colleagues grew chickpea plants (Cicer arietinum) in samples of simulated lunar soil that they treated in two ways: by adding vermicompost — produced by red wiggler earthworms (Eisenia fetida) as they decompose biowaste — at different concentrations; and by inoculating half of the soil samples at each concentration with arbuscular mycorrhizal fungi (AMF). On Earth, AMF improve the nutrient circulation properties of soil, reduce the quantity of potentially toxic metals available for absorption by plants, and produce a protein that helps bind soil together to reduce erosion. The authors then measured the quantity and weight of chickpea seeds produced, along with the plants’ heights and root mass.

The authors found that chickpeas could only flower and produce seeds in samples treated with both AMF and vermicompost. Compared with control plants grown in 100% commercial potting mix, the treated plants in simulated lunar soil produced a significantly lower number of seeds. However, the average seed weight was comparable between plants grown in 25% and 50% vermicompost and the control plants. AMF-treated plants also had a significantly greater dry shoot and root mass than untreated plants, indicating improved plant growth.

The authors therefore suggest that soil regeneration strategies from Earth may be viable on the Moon. However, they caution that all plants grown in some percentage of lunar soil simulant showed signs of stress compared to the control plants.

In a separate study, Jyothi Raghavendra and colleagues investigated growing conditions for microbes in simulated Martian soil. For 60 days, they measured the mass of DNA present in 500 milligrams of simulated soil, kept in a sterile environment at 34% atmospheric humidity — comparable humidity to conditions on Mars. The authors found that the DNA mass increased up to day 30, indicating that microbes already present in the soil grew despite the inhospitable conditions. However, the measured DNA mass had decreased back to zero by day 60. Raghavendra and co-authors argue that their results could inform experiments to determine habitability conditions for microbes on Mars.