Scientists managed to grow plants in artificial Martian soil. In the future, this method could be used by colonists on the Red Planet.
Scientists have managed to grow the first-ever plants in artificial Martian soil by enriching them with symbiotic nitrogen. Plants successfully formed nodules with symbiotic bacteria and showed a twofold increase in biomass. However, scientists were unable to achieve the initially expected enrichment of the soil with nitrogen. The experiment proves that growing plants on Mars will become possible at some point in the future but difficult.
Growing plants on Mars: How can future colonists grow their own food?
Leguminous plants
The roots of leguminous plants (including sweet clover) form specific nodules where symbiont bacteria from the Rhizobiaceae family live. These bacteria fix atmospheric nitrogen, that is, they convert gaseous nitrogen (N 2 ) inaccessible to plants into an easily assimilated ammonium form (NH 4). As a result, legumes grow better, and the soil is enriched with nitrogen available to other plants.
Cultivation on Mars
The cultivation of legumes could help colonize Mars, since the Martian regolith, although it contains nitrogen, is insufficient. But it is still unknown whether the symbiosis of legumes and rhizobial bacteria will work in such soil. Franklin Harris and his colleagues at the University of Colorado decided to test this and conducted an experiment to grow melilot in artificial Martian regolith.
What kind of soil did they use?
The model soil used in the experiment bears the designation MMS (Mojave Mars Simulant), it was developed in 2007 by specialists from the NASA Jet Propulsion Laboratory based on data from spectral observations of the surface of Mars, and landing missions, in particular, the Viking probes and the Spirit rovers and Opportunity.
What is the artificial Martian soil made of?
The basis of the artificial regolith is basalt sand from the American Mojave Desert. It is 50 percent silicon dioxide and 10 percent iron oxide. Melilot sprouts were grown under optimal conditions – in a greenhouse under Phyto-lamps at a temperature of 25-30 degrees Celsius and daily moisture.
Two weeks after planting
Two weeks after planting, ten shoots in the imitation of the Martian regolith were treated with a culture of the bacteria Sinorhizobium melioti, which form a legume-rhizobial symbiosis with melilot, and five more were left untreated. For comparison, the same experiment was carried out in ordinary soil for growing plants.
Three months later
Three months after the treatment, the authors carefully removed the plants, determined their mass and number of nodules, and also analyzed the composition of the soil.
How successful was the experiment? Did scientists find a way to grow plants on Mars?
On the roots of sweet clover in the regolith, nodules were successfully formed, although much less than in the earth’s soil (on average, 14.5 nodules per plant in the regolith, versus 63 in the earth’s soil). The formation of nodules in the regolith could be limited by the high pH and low availability of iron, which is part of nitrogenase, an enzyme that fixes nitrogen.
Other results
The length of shoots, the mass of shoots, and roots in plants with nodules were twice as large as compared with shoots not treated with the culture of bacteria. That is, symbiosis in the Martian soil still works, and significantly improves the life of legumes. However, the accumulation of nitrogen in the regolith with the treated plants did not occur. Despite the work of nitrogen-fixing bacteria, the content of ammonium nitrogen in it even decreased (from 5.5 to 3.7 milligrams per kilogram).
Solutions
The authors attribute this to the fact that in poor soil, the plants consumed all available nitrogen, both formed by bacteria and present in the soil. But there is a possible solution to this problem that will help astronauts grow plants on Mars successfully. In terrestrial agriculture, legumes are often used as “green fertilizers” – they are plowed into the ground, where the plants decompose and release stored nitrogen.
Long-term cultivation of plants on Mars
According to the authors’ assumption, long-term cultivation of legumes and their plowing into the ground will still be able to enrich the Martian regolith with enough nitrogen for plants to grow.
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Sources:
• Colorado State University. (2021, October 1). Crops grow better in Mars soil when given good bacteria, study finds. New Atlas.
• Harris, F., Dobbs, J., Atkins, D., Ippolito, J. A., & Stewart, J. E. (n.d.). Soil fertility interactions with sinorhizobium-legume symbiosis in a simulated martian regolith; effects on nitrogen content and Plant Health. PLOS ONE.
• Rabie, P. (2021, September 29). This could be the plant that sustains early Mars colonies. Inverse.
• ScienceDaily. (2021, September 29). Clover growth in Mars-like soils boosted by bacterial symbiosis.
• Watts, J., & Phillips, S. (2021, September 30). Colorado scientists grow first plants from martian soil. Thred Website.
