The Danish-Greenlandic Environmental Cooperation
Life-giving and lethalSunlight is one of the prerequisites of life on Earth. At the same time, the short-waved segment of the sun's rays can cause sunburn (UVA), destroy plant and animal tissues (UVB) and even kill (UVC). That is why it is so essential to pay attention to what is happening to the ozone layer, which protects us from UV radiation.
A set-up for exposing lichens to UVB radiation at Qaanaaq.
When the sun appears for the first time after the Arctic winter, it is duly celebrated. It has always been like that. But within a few weeks it can already be too much. The ice and snow can make the sunlight completely blinding. In a tanning salon, the UV radiation gives you a tan and the longwaved infrared radiation warms you up. Just like the real high-mountain sun.
First, some information that should be taught in school, but is not, unfortunately, even though it could well be decisive for the continuation of life on earth:
The ozone layer is located above the atmosphere in the stratosphere. Before humans started emitting chlorine and bromine into the atmosphere - from refrigerants, transformers, insulation materials, etc. - the ozone layer was thickest over the poles, and roughly equally thick over the North and South Poles. Chlorine and bromine emissions disturb the fine balance at the bottom of the stratosphere. Atmospheric movements around the North and South Poles respectively are decisive in this process.
Reindeer lichen, Cladonia mitis, thought to be damaged by natural UVB radiation, Qaanaaq.
The Antarctic continent is surrounded by huge bodies of water, which means that the strong air currents over the South Pole stay over Antarctica. This, combined with the extreme cold and the presence of chlorinecontaining substances, speeds up the breakdown of the ozone layer, which in turn increases UV radiation levels, especially in the early spring.
In contrast, on the Arctic end of the globe, there is a large body of water, of ice and surrounded by large landmasses. This means that the bodies of air are much less stable over the Northern Cap. Therefore the breakdown of ozone has not proceeded as fast here, though you might think that it would happen first in the Northern Hemisphere, because that is where the industrial societies - and thus chlorine and bromine emissions - are concentrated.
Ib Johnsen setting up a UVB screen on a heath of white Arctic bell-heather at Qaanaaq.
When the ozone layer erodes, more UVB radiation can get through to plants and animals on Earth. UVB rays are very aggressive, and very destructive to the genetic material in cells. These rays also destroy a number of enzymes, and significantly increase the risk of disease.
Alpine arnica (Arnica angustifolia) from northwest Greenland.
Because of the dangers of UVB radiation, the ozone layer is a prerequisite of life on Earth.
No sun filter
That is the background for Dancea helping to finance an investigation during the last few years into how Arctic plants react to the new situation. Ib Johnsen, from the Botanic Institute at the University of Copenhagen, says, "Plants used to be well protected against UVB radiation by the ozone layer in both Arctic and Antarctic regions. That means that plants and animals did not waste a lot of energy protecting themselves against UVB radiation. It was not necessary. The ozone layer took care of that. So they are very badly adapted to the new situation, where there is suddenly a lot more UVB radiation."
To illustrate this, various species of composites have been studied, among them the Alpine arnica (see illustration). It turned out that near the equator, all the plants were well protected against UVB, but in the same genus at northern latitudes, protection against the damaging rays of the sun did not seem as significant. Here, there was a wide and random variation with respect to protection against UVB. This was studied in the laboratory. The different species belonging to this genus vary widely in that respect. The closer to the poles you get, the greater the variation.
An experiment on UVB radiation in a greenhouse using reindeer lichen (Cladonia mitis). The lamps and lichens are placed behind a protective curtain. Next to the experiment, there are a number of tobacco plants for educational use. Notice that fifteen or sixteen of the pots at the front have accidentally been placed within reach of the radiation. These plants are very stunted compared to the other tobacco plants.
How do plants protect themselves against UVB? "Plants use two main techniques," continues Ib Johnsen, "the first is by producing a dye, a pigment, one of the ones known as flavonoids. These substances absorb UVB in the outer skin and prevent UVB from penetrating the layer of photosynthetically active cells. These pigments increase in concentration the closer we get to the equator, and decrease the closer we get to the poles. The repair process is another important mechanism. Plants can produce substances that can reassemble what UV radiation splits apart. That is, repair the damage that has occurred. Both ways require that the plant has certain reserves of energy."
Slowed growth
The question, then, is whether plants are damaged or changed by UV radiation.
First of all, the growth of the plants is slowed. The net primary production of the individual plant is reduced, as a biology teacher would say (see illustration, a greenhouse set-up). Secondly, the plants do not produce as much seed. That, however, does not mean as much in Arctic regions, because asexual reproduction is very widespread there.
Thus, the reduction of productivity is most significant.
Along with Henning Heide-Jørgensen, Ib Johnsen has looked at the sensitivity of lichens to environmental influences. Mosses are also sensitive, but they form the abovementioned flavonoids, which lichens do not. One would think that that would leave lichens unprotected, but it turns out that they produce lichen acids, which protect them to some degree from UVB radiation. "This may be a coincidence," says Ib Johnsen, "and since there is a big difference between the ability of lichen acids to absorb UV radiation, we can guess that the species, which, for whatever reason, have more lichen acids will be more dominating in the long run."
Lichens have been used to look at urban pollution levels. Are lichens also especially suitable for studying the effects of UVB radiation?
"Yes, if we want an early sign in vegetation of the damaging effects of UVB radiation, then it is a good idea to look at lichens," answers Ib Johnsen. "Lichens are active year-round. That is, they are also active in the very critical period when the hole in the ozone is especially big, in the spring months, before the snow has really melted. We must remember that lichens and many mosses are photosynthetically active at temperatures near zero or even below. They can actually photosynthesize under the snow before it melts. And we must remember that UVB radiation diffuses very easily. The sky is blue because short wave radiation diffuses best. The snow diffuses the light, and the UVB radiation comes from all sides, as it were. So when there is a lot of UVB radiation, you have some plants - the lichens, which are photosynthetically active and, therefore, a highrisk, group in that period."
A fine balance,
To understand why they are especially sensitive, it is necessary to know a little bit of the natural history of the lichens. The lichen is a double organism: a combination of a fungus and an alga. The alga photosynthesizes, and produces plant sugars, which it then delivers to the fungus. The fungus takes care of water supply and the salt that comes dissolved in the water. It is a very refined co-existence of two organisms, which is ancient - hundreds of millions of years old. The symbiosis is very finely balanced, and the risk of it being disturbed is very high.
In laboratory tests where lichens were exposed to UVB radiation, some external damage could be seen after an exposure that was not much higher than what normally occurs in nature. Besides that, there were also changes in the cells, a symptom of the plants using up a lot of the reserves they held in their cells. This leaves them badly equipped to deal with other stressful situations. In Greenlandic lichens, and in field experiments, similar observations have been made.
White Arctic bellheather at Qaanaaq with reindeer lichen, Cladonia mitis.
"I expect that the lichen group as such will be reduced. The ones that will remain are the species that, more or less by chance, are protected against UVB, because they contain lichen acids that protect them in the same way as the pigments of higher plants," concludes Ib Johnsen.
Environmental protection in Greenland
When you walk in the Greenlandic landscape, the terrain is almost entirely covered with lichens in many places.
Lichens live and grow for hundreds, indeed thousands, of years. The growth rate of lichens is known pretty certainly, because the same areas have been photographed at ten-year intervals, so it is possible to guess the age of an exposed surface from the diameter of the scab-shaped lichens on it.
If UVB radiation slows their growth, this method will not be useful much longer.
At the same time, it is a warning about the environmental factors that influence all living organisms.
If lichens do not grow as well, it can mean a lot for many animals. If, for example, reindeer lichens dwindle drastically, then we have to watch the reindeer populations and their reactions. The reindeer population is limited not least by its prospects for winter food, which consists primarily of the reasonably nutritious reindeer lichens. Thus, a decline in reindeer lichens can mean a decline in the reindeer population.
When the hunters go out in the early spring to hunt seal, the eyes of both the hunters and the seals are especially exposed.
"If I were Greenlandic, and interested in the protection of the environment, I would take this pretty seriously. I would not be so worried about changes in lichen vegetation. That probably doesn't mean so much. It will take a lot of UVB radiation to make it a big problem for the reindeer population. But I would be worried about human health, especially sight. The Arctic regions have significant increases in UVB radiation in the early spring months," concludes Ib Johnsen.
Thus, lichens can be used as measuring instruments to show some of the biological effects of UV radiation on some of the plants that are always out there. Lichens could be used as indicators. The damage in itself is not most important: it is the effects derived from it on animals and humans that are most important.
A healthy example of reindeer lichen, Cladonia mitis, from Tisvilde.
