In the lab, the scientists started their investigations by storing lichen samples from the Mojave Desert for different periods of time. In their natural habitat the lichens in the crusts alternate between drying out and hydration. During the desiccation process, they suffer from cellular damage but once they are hydrated repair and growth is possible. In their experiments, the researchers watered the stored samples and then monitored their recovery. “Healthy specimens become active within a minute of watering and compromised lichens go through a period of repair before they become productive,” Sun says. The researchers assumed that those lichens that showed no activity after 8 hours were dead.

Using this methodology, the scientists found that lichens can be stored dry at room temperature in ambient air for up to a year without any significant decline in vitality.  One-year old samples showed similar behavior to fresh samples: once they were given water they were ready to use light energy and photosynthesize.  Three and even ten-year-old samples were weaker and it would take them between 25 and 200 minutes to restore photosynthesis after the addition of water.

The scientists then attempted to determine how ultraviolet (UV) rays would impact the lichens when they were reintroduced back into the desert. The crust lichens protect themselves from UV light by synthesizing compounds that create a screen that blocks the harsh rays.  Even when the researchers put intense UV source as close as 25 centimeters away for one week the lichens suffered only minor damage. “It was well within their ability to repair,” Sun says. “This level of ionizing radiation resistance is unparalleled in the microbial world.”

The scientists did find, however, that the lichens were vulnerable to high concentrations of ozone. Fumigation in ozone for long periods caused photochemical oxidation, killing Collema, a cyanobacterial lichen, and severely damaging Placidium, a green algal lichen. Previous studies on the stress tolerance of crust-forming organisms considered only the impacts of UV radiation and desiccation. “Our work showed that photochemical oxidation presents a more severe stress than UV and desiccation,” Sun says. “And this has implications for crust storage and restoration.”

Given the evidence that the crust lichens are primarily vulnerable to oxidation, Sun recommends that the samples be stored in a non-oxidizing gas, such as nitrogen, instead of ambient atmosphere, to minimize oxidative stress.  In the field, amending the soil with antioxidants could protect the newly restored “seed” organisms from oxidation and thereby help them grow faster.  Both the ability of the organisms to be stored and their ability to survive typical desert conditions bodes well for the future, Sun says. “The research suggests that crust restoration is feasible and should be considered by land managers and solar companies,” Sun says.