Inside a research greenhouse at Colorado State University, Franklin Harris and his colleagues placed clover seeds in sterilized plastic pots stacked next to each other on a bench.
As the familiar leaf began to sprout, emerging from the dirt, the team realized they had accomplished something extraordinary. These were not average clover plants, but instead clover plants grown in Martian soil.
“Clover is somewhat hardy, meaning it can tolerate stressful conditions for plants,” Harris, a researcher at Colorado State University, who led the experiment, tells Inverse. “Given that Martian terrain and conditions will be stressful for plants, I wanted something that could handle tough conditions but also grow fast enough to make a difference within a reasonable amount of time.”
The findings were detailed in a study published Wednesday in PLOS One.
The recent experiment is a crucial step in humanity’s vision of inhabiting a planet other than Earth, addressing the need to grow plants and crops to maintain a sustainable environment.
As scientists search for a place that could potentially host humans, Mars is at the top of the list.
The Red Planet resembles Earth, as a rocky planet with a similar size and composition to our own. But Mars’ soil is not agriculture friendly, owing to a bevy of hazardous chemicals and lacking others to sustain life.
“There are a plethora of challenges that plants must overcome to grow in the material present on Mars,” Harris says.
The soil on Earth is rich in nutrients and microorganisms that help fuel the growth of plants. The Martian surface is covered in an inorganic surface of loose deposits that blanket over rock.
Mars’ regolith lacks micronutrients and nitrogen, the most crucial nutrient needed for plant growth after carbon, water, and oxygen.
“To successfully grow plants, we need them to overcome all of these challenges and likely more,” Harris says. “Just like we can tackle the problems involved with putting a spacecraft into orbit, we can also engineer ways around the problems with this regolith.”
WHAT’S NEW — To overcome these challenges, Harris and his colleagues thought of supplementing the plants with bacteria to fulfill their nitrogen needs. The team got the idea from an agricultural strategy called companion cropping.
Native Americans grew corn, squash, and beans together since corn has a high need for nitrogen, and beans can replenish nitrogen in the soil using their symbiotic relationship with bacteria.
“When I saw the chemical content of regolith, I thought it seemed like a decent idea to use something similar to try to get some bioavailable nitrogen into the system,” Harris says.
The team created a regolith similar to that found on Mars:
- They used sterilized plastic pots and sterilized trays
- Each plot got its own pot and tray, and the researchers spaced the plants out to avoid contamination
- The team then randomized the plants on the bench so that the differences in sunlight wouldn’t be a factor
- The researchers introduced bacteria afterward by creating a dilution from pure cultures that had been grown from a sample
The researchers found that the clover plants with the bacteria experienced 75 percent more root and shoot growth than those without bacteria.
“I [chose clover] because I wanted something that I could grow densely, quickly, and that would have a focused purpose of modifying soil conditions instead of immediate production of food,” Harris says.
WHY IT MATTERS — The recent experiment shows that future astronauts could modify Martian soil to grow plants.
Space explorers currently have their eyes set on Mars as the first planetary destination for humans. Should humans make it all the way to the Red Planet, they plan on staying.
Ideas of colonizing Mars have been circulating recently, with plans of possibly terraforming the planet to accommodate humans.
WHAT’S NEXT — This experiment is the first step.
“I would absolutely be open to running more experiments to make regolith more fertile,” Harris says.
Harris also believes that this recent experiment can help scientists better understand soil and agriculture on Earth and may help us create a more sustainable environment on our home planet first.
“If we are to overcome many of the challenges Mars presents, it may behoove us to look for a deep and insightful understanding of how soil microbes function on Earth,” Harris says. “However, on the same note, requiring people to solve the problems Mars presents, may lead to a better understanding of technology that can be helpful here on earth.”
Abstract: Due to increasing population growth and declining arable land on Earth, astroagriculture will be vital to terraform Martian regolith for settlement. Nodulating plants and their N-fixing symbionts may play a role in increasing Martian soil fertility. On Earth, clover (Melilotus officinalis) forms a symbiotic relationship with the N-fixing bacteria Sinorhizobium meliloti; clover has been previously grown in simulated regolith yet without bacterial inoculation. In this study, we inoculated clover with S. meliloti grown in potting soil and regolith to test the hypothesis that plants grown in regolith can form the same symbiotic associations as in soils and to determine if greater plant biomass occurs in the presence of S. meliloti regardless of growth media. We also examined soil NH4 concentrations to evaluate soil augmentation properties of nodulating plants and symbionts. Greater biomass occurred in inoculated compared to uninoculated groups; the inoculated average biomass in potting mix and regolith (2.23 and 0.29 g, respectively) was greater than the uninoculated group (0.11 and 0.01 g, respectively). However, no significant differences existed in NH4 composition between potting mix and regolith simulant. Linear regression analysis results showed that: i) symbiotic plant-bacteria relationships differed between regolith and potting mix, with plant biomass positively correlated to regolith-bacteria interactions; and, ii) NH4 production was limited to plant uptake yet the relationships in regolith and potting mix were similar. It is promising that plant-legume symbiosis is a possibility for Martian soil colonization.