The Extremotolerant Desert Moss Syntrichia caninervis Is A Promising Pioneer Plant For Colonizing Extraterrestrial Environments

Many plans to establish human settlements on other planets focus on adapting crops to growth in controlled environments. However, these settlements will also require pioneer plants that can grow in the soils and harsh conditions found in extraterrestrial environments, such as those on Mars.

Here, we report the extraordinary environmental resilience of Syntrichia caninervis, a desert moss that thrives in various extreme environments. S. caninervis has remarkable desiccation tolerance; even after losing >98% of its cellular water content, it can recover photosynthetic and physiological activities within seconds after rehydration.

Intact plants can tolerate ultra-low temperatures and regenerate even after being stored in a freezer at −80°C for 5 years or in liquid nitrogen for 1 month. S. caninervis also has super-resistance to gamma irradiation and can survive and maintain vitality in simulated Mars conditions; i.e., when simultaneously exposed to an anoxic atmosphere, extreme desiccation, low temperatures, and intense UV radiation. Our study shows that S. caninervis is among the most stress tolerant organisms.

This work provides fundamental insights into the multi-stress tolerance of the desert moss S. caninervis, a promising candidate pioneer plant for colonizing extraterrestrial environments, laying the foundation for building biologically sustainable human habitats beyond Earth.

Phenotypic changes and physiological responses of S. caninervis plants during the D-R process

(A) Phenotypic changes in S. caninervis crust during dehydration and subsequent rehydration. (B) Phenotypic changes in individual S. caninervis plants during dehydration (D) and rehydration (R). C–E) Relative water content (RWC), optimal photochemical efficiency of photosystem II (Fv/Fm), and changes in leaf angle of individual S. caninervis. Dry S. caninervis samples were fully hydrated with ultrapure water for 24 h and air dried in the laboratory (∼30% relative humidity, 20°C–22°C) for dehydration treatment. Completely dry mosses were then watered to saturation for rehydration. At each treatment time point, a video camera was used to record phenotypes and provide leaf angle measurements, and samples were collected to measure the RWC and Fv/Fm. Data are presented as means ± SEM, three biological replicates, n = 100 individual plants. Scale bars: 1 mm. Asterisks indicate significant differences from the control group (∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001). — Science Direct

Introduction

Exploring and colonizing extraterrestrial environments is an ambitious goal that may improve long-term human sustainability.1,2,3 Mars is considered to be the most likely planet for future human colonization.4,5,6,7 No life forms have been detected on Mars to date. Therefore, introducing organisms from Earth might be required to produce Earth-like conditions suitable for human life on Mars, a process known as terraforming.8

Terraforming will require the selection of suitable organisms from Earth or the engineering of novel organisms (particularly plants) that can thrive in challenging extraterrestrial conditions. To date, only a few studies have focused on testing the ability of organisms to withstand the extreme environments of outer space or Mars. These studies have primarily focused on microorganisms,9,10,11,12,13 algae,8 and lichens.14,15,16 However, plants such as mosses offer key benefits for terraforming, including stress tolerance, a high capacity for photoautotrophic growth, and the potential to produce substantial amounts of biomass under challenging conditions.

Studies of challenging environments on Earth can inform the selection of plants for growth in extraterrestrial environments. The biological soil crust (BSC) is a widespread type of ground cover often found in arid lands. The BSC consists of organic complexes of cryptogamic plants such as lichens and mosses, microbes such as cyanobacteria, and the secretions from these organisms that become mixed with soil particles.17

The BSC serves as a pioneer substrate in vegetative succession due to its remarkable resilience to intense radiation and its ability to withstand drought and other extreme environmental factors.18,19 This has led to the widespread distribution of the BSC in global desert regions, with up to 70% coverage in some areas.20,21 The BSC significantly enhances the water-holding capacity and structural stability of the underlying sand.20,22,23,24 Moreover, the BSC is a major source of carbon and nitrogen in arid regions, accounting for one-fourth of the total biological nitrogen fixation of terrestrial ecosystems worldwide.25,26 Therefore, the BSC has been referred to as the “living skin” of the Earth, as it plays crucial roles in modulating hydrology, nutrient cycling, and other essential ecological processes.

The extremotolerant desert moss Syntrichia caninervis is a promising pioneer plant for colonizing extraterrestrial environments, Science Direct (open access)

Astrobiology