They provide soft light and a favorable microclimate: quartz stones in the Mojave Desert act as small greenhouses for mosses, researchers report. The plants thrive particularly well under the milky, transparent protective shields, as they are protected from dryness, temperature fluctuations and strong solar radiation. However, enough light shimmers through the stones so that the mosses can still perform photosynthesis, according to the studies of the small habitat.
Plants need moisture, nutrients, favorable temperatures and light – if one of these factors is lacking, specialists are in demand: some plants can also cope with very difficult conditions and could therefore colonize extreme locations. These particularly hardy plants also include some types of moss: they can survive repeated drying out and freezing. These ancient representatives of land plants can be found in the polar regions and in the hot arid regions of the world.
Jenna Ekwealor and Kirsten Fisher from the University of California at Berkeley report that some types of moss are also found in the Mojave Desert in the southwestern United States. There, the inconspicuous plants defy the special challenges of this arid region: In addition to the rare rainfall, there are strong temperature fluctuations and the radiation is intense: “The desert is at high altitude and it gets very hot in summer and very cold in winter. There are also the strong temperature fluctuations between day and night, ”says Ekwealor.
Greenery under stones
In unfavorable conditions, the mosses fall into a kind of sleep at their “normal” locations in the open desert and provide sun protection through dark pigmentation. They only wake up and grow if the very rare rainfall offers the opportunity. Their development is correspondingly modest: they only gain a few millimeters per year. “In the desert, life for all organisms is a tightrope walk between life and death,” says Ekwealor. “However, this also means that small advantages can make a comparatively large difference,” said the scientist, referring to the special living space that she and her colleagues have now literally discovered.
At the beginning of the study there was a coincidence, reports Ekwealor: “We were walking in the Mojave to examine the population and reproductive biology of mosses and I picked up one of the quartz rocks found there and said: Look at this pretty stone Then the researchers’ gaze fell on the spot that the milky, shimmering chunk had previously covered. “While all the surrounding mosses were dry and slumbering, it was green under the stone,” said Ekwealor. However, there are no small oases among the granite stones that are also widespread in the desert. It therefore made sense that the growth is linked to the translucency of the quartz rock.
As the researchers report, it was already known that tiny cyanobacteria do photosynthesis in the protection of translucent rocks. So far, however, this has not been known from representatives of the plants. So the scientists decided to investigate the phenomenon more closely. To do this, they examined the characteristics of the mosses and the lighting conditions under the stones. They also placed temperature and humidity sensors under a few specimens to study the microclimate.
Favorable microclimate in the protection of the stones
Ekwealor and Fisher found that mosses, which live in the protection of the slightly transparent stones, grow about 60 percent faster than the exposed mosses. These are the species Syntrichia caninervis and Tortula inermis. “The surrounding mosses are small and brown – under the stones, on the other hand, they are long and green,” says Ekwealor. “This is because the rock acts as a buffer for the extremes of the climate.” The measurements showed that the average relative air humidity under the lumps is about twice as high as in the area of the exposed soil and the daily temperature fluctuation in the microenvironment was around four degrees Celsius less than in exposed areas.
As far as the investigations of the amount of light required for photosynthesis are concerned, it became apparent that, depending on the size of the stone, between four and 0.4 percent of the incident light shines through the milky quartz material. Apparently this is enough for the mosses to generate energy. It is obvious that the stones also offer protection against intensive UV radiation. Because the plants that grow under the quartz form fewer pigments for sun protection than their counterparts in exposed areas.
“Ultimately, the stones offer the mosses two major advantages: either upgrading their normal habitat, or they can live in an area where they would normally no longer exist,” says Ekwealor. “We have to see the world from the perspective of these tiny plants,” says the moss expert: “A comparatively comfortable living space is created for them under a quartz stone.”
Source: University of California – Berkeley, technical article: PLOS ONE, doi: 10.1371 / journal.pone.0235928