THE OZONE LAYER, SOIL AND PLANTS (WITH REFERENCE TO INTERNATIONAL YEAR OF LIGHT AND INTERNATIONAL YEAR OF SOILS)
The ozone layer is a thin, invisible layer that surrounds the Earth like a shield, protecting us from UV radiation. Made up of ozone (O3) molecules that together form a protective net blocking most of the harmful rays of the sun, the ozone layer is located in a part of the atmosphere called the stratosphere. Located between 10 and 50 kilometres above us, it is vital in preserving life on Earth. Ozone is exceptionally important because it absorbs harmful and hazardous UV rays that reach the Earth from the Sun, thus protecting the Earth’s surface and all of life on it.
The concentration of ozone in the atmosphere varies with regard to temperatures, climate conditions, height and so on. Natural as well as anthropogenic events and substances have been found to adversely affect the ozone layer. A volcanic eruption is a natural event that causes the depletion of the ozone layer by ejecting huge amounts of particles and aerosols into the air. However, holes in the ozone layer are primarily the result of anthropogenic effects, that is, substances that deplete the ozone layer. The most widely known of these human-produced substances include freon (used in refrigerators, freezers, air-conditioning, etc.), halon (used in fire-extinguishers), methyl bromide (used in agriculture for soil disinfection), solvents and others.
In addition to depleting the ozone layer, these substances also have an exceptionally high greenhouse effect (some are even 14000 times stronger than CO2) thus impacting global warming. Today ozone-depleting substances have been replaced with other substances that do not have such an effect. The Montreal Protocol signed on 16 September 1987 was central in bringing about this crucial change in the habits and behaviour of society. The Montreal Protocol is an example of a successful international treaty which was brought about by the necessity of preserving the ozone layer. The treaty clearly specifies harmful substances, and stipulates measures and deadlines for the phasing out of the production and consumption of ozone-depleting substances to prevent any further depletion. September 16, the day the treaty was signed, has been proclaimed the International Day for the Preservation of the Ozone Layer. The latest data of the UNEP – Ozone Secretariat (http://ozone.unep.org/en/precious-ozon) indicate that the production of substances controlled by the Montreal Protocol has been reduced to a minimum and the consumption of ozone-depleting substances at the global level has been decreased by 98%. Nevertheless, it is still vital that we continue to respect the ozone layer and to protect ourselves from excessive exposure to the Sun’s rays and UV radiation.
How does UV radiation affect the soil and plants?
While the effects of ultraviolet radiation (UV-A, UV-B and UV-C radiation) on people and health in general are well known, in 2015, the International Year of Soils and the International Year of Light it seems appropriate to learn about, or recall, how UV radiation affects the soil, organisms that live in the soil, and plants. The interaction that occurs is unusually diverse and complex, but still poorly studied and explained. What we do know is that ultraviolet radiation is a key factor affecting the biotic component and biological wealth of planet Earth, and the overall complexity of interactions between living beings and bio (geo) cenosis.
To begin with, it is interesting to note that UV radiation affects global warming via soil and plants. Namely, UV rays stimulate the discharge of volatile organic compounds from soils as well as from plant residue on the surface of the soil and from living plants. The volatile compounds generated by plants have vital protective features. For example, they protect plants, their tissues, cells and genetic material, from the widest range of adverse effects, including excessive UV doses. Released into the atmosphere, these volatile compounds join other types of greenhouse gases, thus changing the composition of the atmosphere and reinforcing global warming. Because higher temperatures (as a result of the greenhouse effect) lead to larger quantities of volatile compounds being released from soil, plant residue and plants, this entire mechanism acts as a feedback loop, increasing its own intensity and action. However, compared with other greenhouse gases, volatile organic compounds probably account for only a small percentage of the overall phenomenon.
UV radiation also affects the mechanism responsible for decomposing plant residue and the processes by which humus and fertile soils are created. Under the impact of UV-B rays, plants undergo a change in the structure and composition of their tissues. Phenolic compounds are among the major products plants produce as protection against harmful radiation. A multitude of different forms of these compounds have emerged and diversified through long evolutionary processes. While phenolic compounds protect plant tissues and cells from the adverse effects of UV-B radiation, they also affect microbes that are active in decomposing plant residue. Thus, vital soil-forming processes are affected, indirectly, through chemical compounds induced in plants by UV radiation.
Although most people associate ultraviolet radiation with adverse, or even lethal, effects to health (sun burn and the risk of skin cancer), we should not overlook the fact that UV radiation also has a positive role and effects. Damage to genetic material (deoxyribonucleic acid – DNA) and resulting gene mutations caused by UV radiation are vital forces and drivers of evolution. Mutations drive the creation of new characteristics and new species of life on our planet. The wide diversity of varieties of crop cultures is the result of mutation, in part triggered by the UV radiation of the sun. On the other hand, blue light and UV radiation play a crucial role in repairing damaged genetic material. This is a process known as photoreactivation and it is a major protective mechanism against UV damage in plants.
Scientists have discovered that in addition to causing DNA damage in cells, UV radiation in plants also affects photosynthesis, respiration, water management and plant growth and development. Plants generally respond to UV radiation by increasing the concentration of different UV-absorbing substances. Algae produce mycosporine-like amino acids as protection against radiation. Seed plants produce an entire spectrum – some 8000 different types – of phenolic compounds, so-called plant secondary metabolites, which possess specific chemical structures characterised by a phenolic (aromatic) ring in the molecule.
Phenolic compounds in plants belong to a group of powerful antioxidants and are beneficial to people as well. Because the human body cannot synthesize phenolic compounds, they must be absorbed through food. Plants growing in environments with increased solar radiation are especially beneficial to people because UV radiation stimulates the production of large amounts of secondary metabolites. Important sources of phenolic compounds include many different types of green plants, as for example, medicinal herbs, as well as fruits and vegetables, some types of grain, tea plants, coffee plants, beans, varieties of red grapes (red wine) and many other types of plants.
Marko Randić (PI „Priroda“)
Tanja Fatur (Office for Environmental Protection, Spatial Planning and Construction)
Category: Interesting facts about Nature, Gaea, celebrating dates in nature and environmental protection
Key words: UV radiation, ozone layer, effect of UV radiation on plants and soil, phenolic compounds
Posted in September 2015
The ecosystems of polar regions have suffered the most from the negative effects of damage to the ozone layer and the appearance of ozone holes, as well as from the resulting increase in UV radiation. Increased UV radiation affects global warming via soil and plants that discharge large quantities of volatile organic compounds. On 27 March 2009, the Croatian Post issued a themed postal stamp and First Day Cover focused on the protection of polar regions and glaciers to help raise awareness of this issue (source: www.posta.hr/default.aspx?id=744&teme=12&m=1803)