Terraforming Mars: Moss

The idea of colonizing Mars, no matter how wild it may be, still haunts many people. But such a move is strikingly different from changing a city or even a country. In order for future colonists to survive on Mars with its unfavorable conditions, it is necessary to take into account many factors, from environmental resistance to sustainable sources of energy, air, water and food. Speaking of food, many studies are aimed at studying plants that can grow in controlled conditions. However, relying only on them would be unwise, so it is worth considering the possibility of planting plants in the soil of Mars. The conditions on Earth and Mars are very different, but, as scientists from the Chinese Academy of Sciences (Beijing, China) have established, among the representatives of the Earth's flora there are specimens that could survive even on Mars. What kind of plant is this, how did scientists determine its resistance to Martian conditions, and how useful will it be for potential colonists? We will find the answers to these questions in the scientists' report.

Research basis

Despite the incredible technological progress, our technologies still remain limited if we consider them as tools for implementing very ambitious ideas. One of them is the colonization of other planets. According to numerous studies, there are planets that are potentially similar to ours, but they are located so far from Earth that reaching them, not to mention colonizing them, is only possible on the pages of science fiction. A much more realistic candidate for colonization is Mars. The minimum distance between Earth and Mars is 55.76 million kilometers, which can be covered (under the best conditions) in about 9 months. Naturally, a long flight is far from the only problem of colonizing Mars. In order to describe all the others, it would take a lot of time, not to mention the human efforts needed to overcome them.

One of the problems of colonizing Mars is food. Of course, you can take it with you, but it will clearly not be enough, and constant supplies of provisions will cost a lot of money. Therefore, it is necessary to think about your own production on site. Most research is aimed at studying crops in the context of growing them in controlled conditions. However, sooner or later you will have to think about growing something in the soil of Mars itself.

To date, only a few studies have focused on testing the ability of organisms to withstand the extreme conditions of space or Mars. These studies have primarily focused on microorganisms, algae, and lichens. However, plants such as mosses have key advantages for terraforming, including stress tolerance, high photoautotrophic growth capacity, and the ability to produce significant amounts of biomass in challenging environments.

Research into the complex conditions on Earth can help in selecting plants for cultivation in extraterrestrial environments. Biological soil crust (BSC) biological soil crust) is a widespread ground cover type often found in arid lands. BSC consists of organic assemblages of cryptogamic plants such as lichens and mosses, microbes such as cyanobacteria, and the secretions of these organisms that are mixed with soil particles. BSC serves as the first substrate in vegetative succession due to its remarkable tolerance to intense radiation and its ability to withstand drought and other environmental extremes. This has led to the widespread occurrence of BSC in desert regions worldwide, with up to 70% coverage in some areas. BSC significantly enhances the water-holding capacity and structural stability of the underlying sand. Moreover, BSC is a major source of carbon and nitrogen in arid regions, accounting for one-quarter of all biological nitrogen fixation in terrestrial ecosystems worldwide. Therefore, the BSC is called the “living skin” of the Earth, as it plays a critical role in regulating hydrology, nutrient cycling and other important processes.

Among land plants, mosses are often pioneer species that are naturally selected to grow in extreme conditions. Moss crusts represent an advanced stage of BSC development. Compared to algal and lichen crusts, moss crusts have greater biomass and carbon sequestration capacity, so they play an important role in biogeochemical cycles and stabilize the desert surface.

Syntrichia caninervis

Syntrichia caninervisa common dominant species in moss crusts, has remarkable tolerance to a variety of environmental stress factors (drought, cold and radiation), giving it a great ecological advantage in harsh natural habitats. S. caninervis has a wide global distribution, as evidenced by geographical data from field studies and the Global Biodiversity Information Facility (GBIF) database.1A).

Image #1

Corky S. caninervis are prevalent in arid regions, including the Gurbantunggut and Tengger Deserts in China and the Mojave Desert in the United States. S. caninervis are also present in the mountainous regions of the Pamirs, Tibet, the Middle East, Antarctica and the circumpolar regions. The Gurbantunggut Desert in northwest China contains one of the most concentrated distribution sites S. caninervis in the world (1B). According to meteorological monitoring from 2005 to 2023, the lowest and highest temperatures in this desert were about 40°C and 65°C respectively, and the relative humidity was only 1.4%.

This extreme climate has created a remarkable resilience S. caninervis to various environmental factors. Plants S. caninervis exhibit extreme resistance to desiccation, typically appearing black when completely dry in the wild after losing over 98% of their water (1C). Remarkably, the dried plants turn green and quickly regain their photosynthetic capacity within seconds of rehydration (1D). S. caninervis has evolved several morphological mechanisms to adapt to extreme environmental conditions, including overlapping leaves that conserve water and protect the plant from intense sunlight and white awns on the leaf tips that reflect strong solar radiation and improve water use efficiency (1D And 2B). Moreover, these plants remain photosynthetically active under snow cover (1E) and can maintain vigorous growth, contributing up to 49% of their annual total carbon fixation during frequent freeze-thaw cycles in the spring. S. caninervis also demonstrates high tolerance to extremely low temperatures.

In the work we are considering today, scientists studied the exceptional stability S. caninervis under conditions of extreme desiccation, extremely low temperatures and intense radiation, as well as in a simulated Martian environment that combines several of these stress factors.

Research results

Image #2

To study tolerance S. caninervis to severe desiccation, the scientists subjected the moss to air-drying conditions in the laboratory and recorded the plant phenotypes, relative water content (RWC) relative water content), optimal photochemical efficiency of photosystem II (F_v/F_m) and changing the angle of the leaves. Plants S. caninervis had extreme drought tolerance, which was demonstrated by their ability to be completely dehydrated and recover very quickly (image above). The plants appeared green when saturated with water, turned dark green and then black as they gradually lost water, and turned green again only 2 seconds after rehydration (2A And 2B). RWC decreased gradually and steadily as dehydration progressed: more than 40% of water was lost in 10 minutes and more than 99% in 40 minutes. RWC of dehydrated plants S. caninervis increased to more than 80% after 20 seconds of rehydration and was restored to 100% after 2 minutes (2C).

F values_v/F_mwhich reflect photosynthetic capacity, decreased significantly as dehydration progressed, decreasing by 54% after 20 minutes to almost zero after 40 minutes of dehydration. Within 20 seconds of rehydration, F_v/F_m was rapidly restored to 65% of baseline in hydrated plants and increased to baseline within 2 min (2D). When dehydrated, the leaves visibly curled and wrinkled, and the leaf angles decreased. During rehydration, the leaves stretched and returned to their original position within 20 seconds (2E). Thus, plants S. caninervis can withstand extreme stress associated with dehydration and have the ability to quickly restore their physiological activity within seconds.

Image #3

To study plant tolerance S. caninervis to prolonged exposure to extreme cold temperatures, the scientists exposed fully dry (0–2% RWC) and fully hydrated (100% RWC) plants to –80°C in an ultra-low temperature freezer for 3 or 5 years and –196°C (in a liquid nitrogen storage tank) for 15 or 30 days. The plants were transferred to sand for recovery and cultured under normal growth conditions to observe their ability to regenerate. The experimental setup is shown in 3A. Dry plants S. caninervis survived and regenerated new branches after low-temperature treatment (3B). Without freezing treatment, the number of regenerated new branches in plants S. caninervis 5 days after rehydration it was approximately 1–2 per plant and reached a maximum (3) 30 days after rehydration.

When exposed to –80 °C for 3 years, the number of new regenerated branches after 5 days of recovery (in sand under normal growth conditions) was 0.22 ± 0.15. The maximum number of branches was slightly lower after 30 days of recovery (2.22 ± 0.40) (3C). After exposure to –80 °C for 5 years, the number of regenerated new branches was 0.10 ± 0.10 on the 5th day of recovery, and the maximum number of branches was 1.90 ± 0.18. During the recovery period, the number of regenerated new branches after 5 years of exposure to –80 °C was slightly, but not significantly, lower than after 3 years (3C). For untreated plants, the regeneration rate after dehydration reached 75% on the 5th day and 100% on the 15th day after rehydration. For plants S. caninervistreated at –80 °C for 3 or 5 years, regeneration rates were significantly lower than those of the control after 5 days of recovery (10% and 5%, respectively), but increased to approximately 90% after 30 days of recovery (3D).

Image #4

For gamma irradiation experiments, fully dry (0–2% RWC) and fully hydrated (100% RWC) samples S. caninervis were exposed to total doses ranging from 500 to 16,000 Gy, rehydrated and transferred to sand for recovery and culture under normal growth conditions (4A). A dose-dependent effect on survival and regeneration was found (4B). For untreated controls (0 Gy), after rehydration and recovery period, the average number of regenerated branches increased over time, reaching 100% after 60 days of recovery, with a maximum number of regenerated branches of 3.24 ± 0.23 per plant (4B–4D). At irradiation doses of 500 and 1000 Gy, the number of new regenerated branches after 7 days of recovery was 2.96 ± 0.14 and 2.86 ± 0.16, respectively (4C). By the 60th day of recovery, the regenerated branches had grown and their number was greater than in the control group for each dose: 4.08 ± 0.21 and 3.57 ± 0.18 for 500 and 1000 Gy treatments, respectively. The regeneration rate after both treatments was 100%. Thus, 500 Gy radiation strongly promoted the regeneration of new branches (4D). When the radiation dose was increased to 2000 Gy, regeneration was delayed, and new branches appeared only 14 days after recovery (4B). At this time, a lower average number of regenerated branches (0.52 ± 0.12) was found (compared to other treatments), although the number of regenerated branches increased to 2.03 ± 0.16 at a regeneration rate of 90% after 60 days of recovery (4C And 4D).

At a radiation dose of 4000 Gy, the moss samples showed signs of stress: the leaves gradually turned yellow after 3 days of recovery (4B). After 14 days of recovery, new branches began to regenerate (on average 0.22 ± 0.12). After 60 days of recovery, the average number of branches reached 1.20 ± 0.15 with a regeneration rate of 70% (4C And 4D). Doses of 8,000 and 16,000 Gy of radiation caused serious damage to the moss samples: the leaves turned yellow and died without forming new branches (4B–4D), and photosynthetic activity was not detected. Based on these results, the scientists calculated that the LD50 (lethal dose at which 50% of organisms survived) occurred after 1 hour of exposure (LD50/1 hour) at a dose of 5000 Gy. Moreover, when fully hydrated plants S. caninervis were subjected to the same gamma irradiation treatment, they survived and regenerated, although at LD50/16 min 2000 Gy. The rate of regeneration and the number of newly formed branches were lower than in plants in a dry state.

Image #5

To gain a deeper understanding of the possibility of survival S. caninervis Under more realistic combined stress conditions, scientists simulated the harsh environment of Mars using the Planetary Atmosphere Simulation Facility (PASF) Planetary Atmospheres Simulation Facility) (5A–5C). Plants S. caninervis survived in simulated Martian conditions (5D–5F). In untreated plants, after 3 days of cultivation, there were 0.86 ± 0.18 regenerated branches, while in treated plants, after 3 days of cultivation, no new branches were found to be regenerated. The number of regenerated new branches in untreated plants reached a maximum (3.13 ± 0.25) after 30 days of cultivation, while the maximum number of new branches in plants treated for 1, 2, 3, and 7 days and allowed to recover for 30 days was 2.00 ± 0.25, 2.07 ± 0.23, 1.82 ± 0.12, and 1.42 ± 0.10, respectively (5E). The regeneration rate of untreated plants reached 50% after 3 days of cultivation and 100% after 15 days, whereas dry plants treated for 1, 2, 3 and 7 days required 30 days of recovery to reach 100% regeneration rate (5F). When the plants are fully hydrated S. caninervis When exposed to Mars conditions for 1 day, the plants also survived and regenerated branches, although the number of branches and the rate of regeneration were sharply reduced compared to those of dry plants.

For a more detailed look at the nuances of the study, I recommend taking a look at scientists' report And Additional materials to him.

Epilogue

In the work we have reviewed today, scientists studied moss of the species

Syntrichia caninervis

which has amazing resistance to extreme environmental conditions. Scientists claim that such plants can be used in the process of terraforming Mars.

The scientific community has previously conducted similar studies, but on algae, microorganisms, lichens and plant spores. The study of complete plants (i.e. whole plants, not their components), especially mosses, has not been conducted before.

During the experiments Syntrichia caninervis were exposed to low temperatures: -80 °C (in an ultra-cold freezer) for 3 and 5 years, and -196 °C (in a liquid nitrogen tank) for 15 and 30 days. After defrosting, all plants showed branch regeneration. Moreover, dried and then frozen samples recovered much faster than hydrated ones.

Even more surprising was the ability of this moss to withstand high levels of gamma radiation. By the way, a dose of 50 Gy can be fatal for a human, while Syntrichia caninervis not only withstood a dose of 500 Gy, but also grew better.

The most revealing experiment was the simulation of Mars conditions: air with 95% CO²temperatures from -60 °C to 20 °C, high UV radiation and low atmospheric pressure. Dried moss plants achieved 100% regeneration rate within 30 days after exposure to Martian conditions for 1, 2, 3 and 7 days. Hydrated plants that were exposed to the simulator for only one day also survived, although they regenerated more slowly than the dried ones.

Scientists do not deny that it will take much more effort and time to create a fully-fledged and self-sufficient habitat on Mars. But their work is one of the first steps towards achieving this goal. In the future, scientists would like to conduct field tests by delivering this moss to the Moon and Mars in order to understand its properties in real conditions.

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