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Ozone Depletion & Land Vegetation

Introduction

Excessive UV-B inhibits the growth processes of almost all green plants. There is concern that ozone depletion may lead to a loss of plant species and reduce global food supply. Any change in the balance of plant species can have serious effects, since all life is interconnected. Plants form the basis of the terrestrial food web, prevent soil erosion and water loss, and are the primary producers of oxygen and a primary sink (storage site) for carbon dioxide, a greenhouse gas.

UV-B and Land Plants

Exposure to UV-B radiation may have a dramatic effect on terrestrial plant life, although the impacts are at present poorly understood. Absorption of UV radiation varies widely from one organism to the next. In general, UV radiation deleteriously affects plant growth by reducing leaf size and limiting the area available for energy capture during photosynthesis. Plant stunting and a reduction in total dry weight are also typically seen in UV-irradiated plants, with a reduction in the nutrient content and the growth of the plants, especially in the legume and cabbage families. A reduction in quality of certain types of tomato, potato, sugar beet and soya bean has also been observed. Forests also appear to be vulnerable. About half of the species of conifer seedlings so far studied have been adversely affected by UV-B at a variety of levels. Although old needles are able to protect themselves by strengthening their outer wax coating and by increasing the amount of protective pigment, young growing pine needles, in contrast, suffer easily.

Indirect changes caused by UV-B radiation (such as flowering and germination rates, changes in plant form and how nutrients are distributed within the plant) may be more important than damaging effects of the radiation itself. These changes can have important implications for plant competitive balance, plant diseases, and biogeochemical cycles. However, reliable scientific information on the effects of UV on plants is limited. Only four out of 10 terrestrial plant ecosystems (temperate forest, agricultural, temperate grassland, and tundra and alpine ecosystems) have been studied. In addition, much of the existing data come from greenhouses where plants are more sensitive to UV-B than those grown outdoors. There are indications that some weeds are more UV-B resistant than crops. Many organisms have developed mechanisms for protecting themselves from UV-B, for example by avoiding exposure, shielding themselves with pigment and repairing damaged DNA or tissue damage. However, for many organisms these mechanisms may not be sufficient to protect against increased levels of UV-B.

In summary, physiological and developmental processes of plants are affected by UV-B radiation, even by the amount of UV-B in present-day sunlight. Despite mechanisms to reduce or repair these effects and a limited ability to adapt to increased levels of UV-B, plant growth can be directly affected by UV-B radiation.

Ozone Depletion and Land Plants

The greatest risks connected with the depletion of ozone in the stratosphere are ecological. Exposure tests made in USA and Australia have showed that over one hundred species of land plant could be sensitive to increases in UV-B radiation as a result of stratospheric ozone depletion. Some research has suggested that a 25% ozone depletion could result in a comparable reduction in total soya bean crop yield.

International research has revealed that some species of rice suffer from even minor increases in UV radiation. With the help of research, as well as the efficient breeding and cultivation of strong species it will be possible to be prepared for years with a considerably decreased prevailing level of ozone.