Clover plants that grow in Mars-like soils experience significantly higher growth when inoculated with symbiotic nitrogen-fixing bacteria than when left uninoculated, according to the results of a study just published in the journal PLOS ONE .
The future of astroagriculture
How to make Martian soils more fertile? On Earth, soil bacteria help convert or “fix” atmospheric nitrogen into molecules that plants need. Some of these microbes have symbiotic relationships with plants, in which they fix nitrogen within the nodules found in their roots.
Now, a team of scientists has explored the possible role of symbiotic nitrogen-fixing bacteria in astroagriculture. To do this, they grew clover in an artificial regolith very similar to the soils of Mars. Next, they inoculated some of the plants with the Sinorhizobium meliloti microbe, which is commonly found in clover root nodules on Earth. Previous research had shown that clover can be grown in regolith, but inoculation with nitrogen fixers has not been explored until now.
Differences with terrestrial soils
The researchers found that inoculated clover experienced 75% more root and shoot growth compared to uninoculated clover. However, the regolith surrounding the inoculated plants showed no signs of elevated NH4, an essential nitrogen-containing molecule for plants, compared to the regolith surrounding the non-inoculated plants.
These findings suggest that symbiotic microbes drove clover growth, but did not result in excessive production of nitrogenous compounds that could hypothetically use other plants in the environment, as occurs in terrestrial soils. In fact, many species of the legume family, such as clover, are called ‘nitrogen fixers’ due to this capacity for symbiosis, and are used as pioneers when it comes to fertilizing soils.
If anything, these findings suggest the possibility that the symbiosis between plants and nitrogen-fixing bacteria could help agriculture on Mars. Future research could continue to explore such relationships with other crops and address problems with plant toxicity in the regolith.
The authors add: “This study shows that the nodule-forming bacterium Sinorhizobium meliloti nodula has been shown in the Martian regolith, significantly enhancing the growth of clover ( Melilotus officinalis ) in a greenhouse trial. This work increases our understanding of how interactions between plants and microbes will aid efforts to terraform regolith on Mars. “
Referencia: Harris et al. 2021. Soil fertility interactions with Sinorhizobium-legume symbiosis in a simulated Martian regolith; effects on nitrogen content and plant health. PLOS ONE DOI 10.1371/journal.pone.0257053