[] TL: OZONE DEPLETION EFFECTS ON PLANTS & ECOSYSTEMS SO: Greenpeace UK, (GP) DT: February 21, 1992 Keywords: environment greenpeace atmosphere ozone europe ec conferences portugal / Submission by Greenpeace to The Council of Ministers (Environment) of The European Community At Their Informal Meeting, Estoril, Portugal, Friday 21 - Saturday 22 February 1992 concerning Effects of Ozone Depletion on Plants and Terrestrial Ecosystems, Marine Organisms and Farm Animal Species and The Requirement for Emergency Action to Reduce Pollution by Ozone Depleting Substances (GP) Dr Susan J Mayer Director of Science Greenpeace (UK) CONTENTS 1. EXECUTIVE SUMMARY 2. THE EFFECTS OF OZONE DEPLETION ON: TERRESTRIAL ECOSYSTEMS AND PLANTS MARINE ORGANISMS FARM ANIMAL SPECIES 3. THE REQUIREMENT FOR EMERGENCY ACTION TO REDUCE POLLUTION BY OZONE DEPLETING SUBSTANCES EXECUTIVE SUMMARY The Effects of Ozone Depletion on Terrestrial Ecosystems and Plants, Marine Organisms and Farm Animal Species. This submission reviews the areas where the effects of increasing UV-B radiation as a consequence of ozone depletion are going to be of particular importance both for the future structure and viability of ecosystems and the production of food plants, marine organisms and farm animal species. The damaging effects of UV-B on plants is well recognised. Photosynthesis is inhibited, growth and development altered and DNA damaged. Although not all plants and varieties are equally susceptible to damage by UV-B there are important crop species which are susceptible. These include barley, oats, soybean, tomato, sugar beet, carrot and kale. Many species of tree used in timber production and some garden plants are also sensitive. Less is known about the possible impacts of UV-B on natural ecosystems but what research has been done shows that changes in ecosystem composition and diversity will occur. Alterations in timing of flowering could be particularly detrimental in alpine and mountain systems where synchrony with insect pollinators is vital. The effects of UV-B on marine ecosystems will be most damaging to those organisms at the base of the food web, the bacteria, phytoplankton, krill, fish eggs and larvae. All of these organisms are found in positions in the water column where they are at risk. UV-B is damaging to DNA, growth and reproduction ln many of these species. Since more than 50% of the world's biomass is in aquatic ecosystems, even small reductions in productivity could have serious implications. Effects on those species at the very base of the food-web will be felt by all those species above them in the food chain. It has been estimated that a sustained 16% decrease in ozone could lead to a 5% reduction in primary production which would result in about a 7% decrease in fish yield which is equivalent to 10 million tonnes of fish per year. 30% of the world's animal protein for human consumption comes from the seas so such reductions could be seriously damaging to human food resources. Coral reefs are also at risk from rising UV-B levels. Many of the epifaunal species are already at their tolerance levels for UV-B and, coupled with other stresses such as increasing sea temperature due to global warming, their future survival is threatened. The damaging effects of UV-B on photosynthesis by terrestrial plants and phytoplankton may mean that they will be unable to respond as expected to rising levels of CO2 by increasing growth. It has been predicted that increased photosynthesis by plant life would absorb some of the CO2 increase due to consumption of fossil fuels. However, a recent study shows that in two out of three species increased photosynthesis resulting from elevated CO2 was abolished by elevated UV-B. In addition, it has been calculated that a loss of 10% of marine phytoplanktan alone would reduce ocean uptake of carbon dioxide by an amount (5Gt) equal to annual emissions from fossil fuel consumption. Such interactions have worrying implications for responses to global warming. Farm animal species are better protected than humans from the damaging effects of UV-B by virtue of their coats and skin pigmentation. However, there are several conditions in farm animals which have been linked with exposure to solar radiation. These include squamous cell carcinomas on the eyes, eyelids and ears of cattle and sheep. An infectious condition of the eyes of cattle (infectious bovine keratoconjunctivitis or New Forest Eye) is considered to be made worse by ultraviolet radiation. In farmed fish there have been reports of cataracts and losses due to skin damage following excessive exposure to solar radiation. Since fish in many aquaculture systems have little protection fran the sun any effects of UV-B on these species will be especially severe. An increase in these conditions in farm species will involve considerable suffering to those individual animals involved and will also lead to economic losses to farmers. Production will be reduced and costs increased because of the inevitable need for treatment. The Requirement for Emergency Action to Reduce Pollution by Ozone Depleting Sources Results of the European Arctic Stratospheric Ozone Experiment {EASOE} and of work by NASA show that active chlorine pollution over the Northern Hemisphere, including European cities, is as high as that within the Antarctic ozone hole. An ozone hole over Europe could be imminent. As sunlight catalyses the reactions causing ozone destruction over the next months, ozone could be lost at a rate of around 1% a day. The EE should take a global lead by calling for an emergency meeting of the Parties to the Montreal Protocol, in order to immediately ban production and use of CFCs and all ozone- depleting chemicals. [Otherwise the Parties are not due to meet until April and not to take a decision to bring forward dates for phaseouts until November]. As a major group of producers of ozone depleting substances, EC countries should all introduce an immediate ban on production of CFCs [refrigerants, propellants, solvents, foam-blowing agents], methyl chloroform [industrial solvent], carbon tetrachloride [primarily used to make CFCs], halons [used in some fire extinguishers], and HCFCs (put forward as 'transitional' replacements for CFCs). 'Essential' medical uses (for life threatening conditions) should be met by recycling. A. THE EFFECTS OF OZONE DEPLETION ON PLANTS AND TERRESTRIAL ECOSYSTEMS 1. Introduction The damaging effects of UV-B radiation on plant life was been recognised for a considerable time and there is a vast literature on the subject which has been regularly reviewed [Teramura, 1983; Krupa & Kickert, 1989; Tevini & Tersmura, 1989; Teramura et al, 1991]. Most of the early experimental work was carried out in growth chambers or in greenhouses. Only more recently have more field experiments been performed. Since many of the experiments have used different means of producing UV-B, often with different spectral characteristics and with varied exposure regimes or methods of protecting plants from UV-B, it is often difficult to make comparisons and to unravel the underlying trends behind the sometimes seemingly contradictory results. The majority of studies have been carried out on crop plants and agricultural weeds, less attention has been paid to wild species of plants. The effects recorded include damage to DNA, alterations in growth, metabolism and reproduction. At least 3 grain crops, 3 legume crops, 8 types of fruit, 9 vegetables and 4 tree species are considered particularly sensitive. Also the combined effects of UV-B and other environmental variables such as carbon dioxide, ozone and water and nutrient availability have only recently been begun to be investigated seriously. This paper reviews the mechanisms by which UV-B is thought to damage plants and the implications this may have for ecosystems or agricultural systems. 2. Effects of UV-B on plants It is not possible to state categorically that all plants will show a specific response to a certain level of UV-B exposure. There are differences not only between species [interspecific] of plants but also between varieties of the same species [intraspecific]. Therefore, an overview is given of the most widely recognised and accepted effects. Many plant processes have been considered to be affected by UV-B radiation. The majority of these are caused at the molecular level by UV-B damage to cellular DNA, photosystern II (part oś the photosynthetic pathway) and via yet to be defined UV-B receptors (Caldwell et al. 1989). The routes by which such effects are thought to result in whole plant and community effects is shown in Figure 1 (omitted here). 2.1 Plant function - Photosynthesis and transpiration Generally UV-B radiation causes a net inhibition of photosynthesis [Teramura, 1983; Tevini & Teramura, 1989: Caldwell et al, 1989]. This effect is considered to be take place through damage to the photosystem II reaction centre leading to reduced CO2 uptake. For instance, Strid et al (1990] measured a 55% decrease in photosystem II activity in pea plants exposed to supplementary UV-B radiation and an 80% decrease in Rubisco activity, an important photsenthetic enzyme. Their studies also showed that such effects on the photosynthetic system were progressive. The depressant effect of UV-B on photosynthesis is more profound at low light levels. Although inhibition of photosynthesis by UV-B radiation is well documented in laboratory studies in a very wide range of plant species including important crop species and trees, results from field experiments tend to much more variable. This may be due to the inevitable variability in conditions during field trials or it may be that protective mechanisms are better able to develop [Caldwell et al, 1989). There are some exceptions however, notably soybean [see below & Tevini & Teramura, 1989 & references therein), where significant reductions in photosynthesis, growth and production of plants is seen in field trials. UV-B radiation can also lead to stomstal closure in plants [Teramura, 1983; Tevini & Teramura, 1989) thereby limiting diffusion of CO2 into the leaf and reducing photosynthesis. 2.2 Plant composition 2.2.1 Photosynthetic pigments Teramura [1983] and Tevini & Teramura [1989) have briefly reviewed the evidence that photosynthetic pigments are damaged by UV-B radiation. Both chlorophyll a and b are sensitive and to a lesser extent, carotenoids. 2.2.2 Non-photosynthetic pigments UV-B radiation induces the rapid production of UV-B absorbing pigments by plants which concentrate on the upper epidermal layers of leaves and act to shield the plant from the damaging effects of UV-B (Teramura, 1983; Tevini & Teramura, 1989). UV-B may act through a UV-B receptor leading to regulation of an enzyme (phenylalanine ammonialyase, PAL) which is of importance in a biochemical pathway called the shikimic acid pathway (Caldwell et al, 1989). Other enzymes in the pathway are also induced by UV-B. Therefore, not only does induction of this pathway lead to the production of flavonoids which act as UV-B protective pigments but also to other products which may influence growth and gene expression. Products of this pathway are also important in plant protection against herbivores and pathogens and the food quality of the plant as well as ultimately influencing decomposition. The importance of the shikimic acid pathway, which is affected by UV-B, has led Caldwell et al (1989) to suggest that important ecosystem effects of UV-B may be mediated, in part, through this mechanism. 2.2.3. Other components Some studies have demonstrated that UV-B irradiance can alter protein and lipid content of plants and seed (see e.g. Lydan et al, 1986) although this is not always expressed as a simple dose-response relationship and there are differences between cultivars and species, some apparently sensitive whilst others are resistant. 2.3 Plant growth and morphology. Teramura (1983) reviewed the gross changes in plant growth and morphology that may be caused by UV-B. These include leaf area and weight, bronzing and glazing of the surface of the plant, stunting and changes in total weight of plant produced. The impact of UV-B will not only be determined by the level of exposure and the intrinsic susceptibility of the plant but also the stage of the life cycle at which it is exposed. For instance, Teramura & Sullivan (1987) concluded that the transition between vegetative and reproductive growth was the most sensitive stage of soybean growth to UV-B radiation. Gould & Caldwell (1983) considered wheat was most sensitive in its earliest stages of growth. Reductions in plant leaf area and weight tend to be seen in conditions of low light and UV-B may increase leaf area under some conditions. However, Barnes et al (1988) have shown that although UV-B did not affect total biomass of wheat and wild oats, there were changes in leaf insertion heights and blade length. Further experiments (Barnes et al, 1990) using UV-B levels equivalent to a 20% ozone depletion, demonstrated that such morphological changes are seen in dicot crops and weeds as well as monocot crops and weeds. Such effects may affect the natural balance between species (see later]. 2.4 Pollination and flowering Although pollen is well protected from UV-B when in the anther and contains its own UV-B absorbing compounds, once transferred to the stigma the pollen tube is exposed and at risk (Tevini & Teramura, 1989). Feder & Shrier (1990) demonstrated a 44% decrease in pollen tube growth in a Nicotiana sp and 59% in a Petunia hybrid. Germination is also delayed by relatively low rates of UV-B exposure and flowering may be inhibited or its timing affected. These findings led Tevini & Teramura (1989) to point out that such effects could have important consequences for natural ecosystems if flowering time alteration led to loss of synchrony with the presence of appropriate insect pollinators. Data on the effect of UV-B on yield is relatively sparse because the majority of experiments on the effects of UV-B have been conducted in the laboratory or greenhouse where it is either not practically feasible to take plants to maturity or the numbers involved are too small to be meaningful. When Teramura (1983) reviewed the literature on the effects of UV-B he identified eight crops in which yield was reduced - potato, beans, cowpea, cabbage, squash, broccoli, mustard and spinach. However, reductions were not seen in all reports and were not always dose dependent. In their 1989 review Tevini & Teramura (1989) also reported that certain soybean cultivars showed reduced yields when exposed to UV-B. Field studies under conditions equivalent of up to 16% ozone reduction did not result in decreased yields of wheat [Biggs & Webb, 1986), Sinclair et al (1990) found similar results with field trials of soybean under 16% ozone depletion. However, Teramura et al (1990) in a six year field trial showed statistically significant declines in the yield of soybean in five out of six seasons when conditions mimicking 25% ozone depletion were used. When UV-B levels equivalent to 16% ozone reduction were used, significant reductions in yield were only seen in one of the six years. Therefore, as well as differences between strains the degree of exposure is also critical. Beggs et al (1986) reviewed the adaptive mechanisms of plants to UV-B radiation. These can be split into three classes: i) where damage is repaired ii) where UV-B reaching sensitive sites is reduced iii) where the plant minimises negative effect The processes when damage is repaired include photorepair of DNA, excision repair of DNA and reconstruction of DNA. Photorepair of DNA is the process where UV-A and visible light initiate a photoenzymatic repair of damaged DNA. This process may explain why some of the effects of UV-B are less evident in high light levels. Excision repair entails the damaged piece of DNA being removed and a new piece resynthetized. Reconstruction of DNA involves the complete replication and construction of undamaged strands. The protection of photoprotective pigments such as flavonoids to act as screening agents has both been demonstrated to occur and to protect against UV-B damage (Beggs et al, 1986). However, protection may not always be complete because the absorbtion characteristics of the compound may have absorbtion maxima outside the UV-B range. Morphological changes in the plant or in the timing of events may serve to protect the plant from UV-B, but such mechanisms are much more speculative (Begg et al, 1986). 3. Relative susceptibility of crop species In their review Krupa & Kickert (1989) chose biomass as an indicator of plant sensitivity to UV-B. It is probably a good measure of the cumulative, complex effects of UV-B on plants (Teramura, 1983). The main classifications they made of crop and tree species are shown in Table 1. It must be remembered that there were great differences between species and between strains as well as in the experimental conditions used in the studies included in preparation of this table. ln addition, some effects of UV-B on plants may not affect biomass. For instance, Barnes et al (1988) showed that although morphology of wheat and wild oats was affected by UV-B, total biomass was not. Therefore classification by biomass excludes some indicators of sensitivity. However, some major agricultural crop species are considered sensitive to UV-B radiation including barley, oats, sweet corn, soybean and peas. Some important vegetables such as tomato, cucumber, cauliflower and broccoli are also sensitive as are the root crops sugar beet, carrot and turnip. Therefore increasing ultraviolet-B radiation following ozone depletion may have important consequences for both animal and human food production. 4. Effects of UV-B on competition between plants species Studies are now beginning to demonstrate that differential effects of UV-B on plant species and varieties may have consequences for plant community structure (e.g. Gold & Caldwell, 1983; Barnes et al 1988; Barnes et al, 1990). ln agricultural systems the Gramineae or grasses [including wheat, oats and rice] seem to be more susceptible than broad leaved plants [such as brassicas] to community changes because of altered competitiveness. Barnes et al (199O) found that although broad leaved weeds and crops did show altered morphology in relation to UV-B this was more marked in weed and crop grasses and cereals. For instance Barnes et al (1988) demonstrated that wheat has a competitive advantage over wild oat but there seems to have been no other recent studies examining crop weed pairs. Therefore it is not possible to predict whether weed or crop will profit from the competition and is likely to depend on the species pair involved. 5. Interactions with other environmental conditions In contrast to the laboratory, plants in the environment will be exposed to more than ons single environmental variable and therefore plants may be exposed to multiple stresses. These include natural stresses such as drought as disease or anthropogenic derived stresses such as ozone pollution, increased UV-B and elevated CO2 levels. The possible implications of the combined effects of such stresses are beginning to be recognised and experiments performed. 5.1 Nutrient and water stress In the presence of nutrient and water stress the effects of UV-B on plants are often altered (Teramura, 1986; Tevini & Teramura, 1989). For instance cucumber resistance to water stress is reduced in the presence of UV-B, while that of radish is not. Soybean production is depressed by water stress but not further by UV-B. UV-B does not appear to further depress photosynthesis in P-deficient soybean plants although photosynthesis was decreased by 20% in plants with good supplies of phosphorus. Thus, the effects of UV-B may be reduced by supplying additional minerals if these are in low supply. 5.2. Disease The recent review by Teramura et al (1991) suggests that sugar beet and cucumber may both be rendered more susceptible to disease by exposure to UV-B. In studies with wheat (Biggs & Webb, 1986) there was not such an association. 5.3 Tropospheric ozone Although ozone in the upper atmosphere [stratosphere] protects the earth from UV-B radiation, when present in the lower atmosphere [troposphere] ozone is toxic. It is considered to be one of the most phytotoxic air pollutants (Krups & Kickert, 1989}. Ozone causes reductions in, among other things, photosynthesis, leaf area, dry matter production and drought resistance. Elevated levels of ozone may not coincide with elevated levels of UV-B but sequential exposure to pollutants to which a plant is sensitive could be damaging. In combination with local ozone, UV-B has been shown to result in delayed pollen tube growth in a Nicotisna sp and a Petunia hybrid [Feder & Shrier, 1990]. These effects were additive and suggest that if elevated UV-B is seen in the presence of elevated ozone, very damaging effects on plants may be seen. 5.4 Carbon dioxide Carbon dioxide levels may double during the next century as a consequence of global warming. UV-B levels are also set to rise during this period as ozone depletion progresses. Although CO2 may stimulate photosynthesis and result in increased yield and total plants biomass, Teramura et al (1990b) have recently shown that in rice and wheat such increases are reversed when ultraviolet B radiation is increased to levels expected with a 10% ozone depletion. This was not seen in soybean. Therefore estimates of global plant productivity following rises in ambient CO2 may need to be reassessed. In addition the ability for plants to absorb rising levels of CO2 and thus mitigate the effects of global warming may be limited by the effects of increasing UV-B radiation. 6. Ecosystem effects Very few studies have considered the impact of increased levels of UV-B on natural communities. Caldwell et al (1982) examined the sensitivity of arctic and alpine species to UV-B and found that arctic species, where natural UV-B levels are low, are much more sensitive to the damaging effects of UV-B than alpine species. At the altitudes and latitudes where alpine species are found, levels of UV-B are up to seven times higher than arctic species would experience. Therefore, UV-B is likely to have exerted a evolutionary selection pressure an alpine plants. Ozone depletion is set to progress and UV-B levels rise rapidly over the next few decades and whether sensitive arctic plants will be able to adapt quickly enough to survive must be questionable. For instance changes to the photosynthetic apparatus would require genetic changes which will respond only slowly to natural selection [Caldwell et al, 1982]. UV-B may also affect natural ecosystems by changing the competitive balance between species as morphological changes affect the physical structure of plant communities (Tevini & Teramura, 1989). ln addition, alterations of the timing of flowering may reduce reproductive success (Tevini & Teramura, 1989). Some of the effects of UV-B on biochemical pathways may alter plant composition which could ultimately lead to altered food quality, nitrogen fixation, decomposition and altered resistance to grazing and disease [see Figure 1 & Caldwell et al, 1989) 7. Conclusions i) Continued research demonstrates the serious potential for damage to crop and wild plant species by elevated levels of UV- B. ii) A wide range of plant species are sensitive to UV-B radiation. There may be inhibition of photosynthesis, altered plant morphology, reduced growth and reproduction. iii) There are wide variations in species and variety sensitivity to UV-B so it is not possible to quantify the likely impact of elevated UV-B on agricultural production. iv) Yield of soybean has been shown to decline significantly under UV-B conditions mimicking 25% ozone depletion. v) Those crops considered to be sensitive to the effects of UV-B include barley, oat, sweet corn, soybean, pea, and cowpea. Sensitive fruit and vegetables include tomato, cucumber, cauliflower, broccoli and carrot. vi) The competitive balance between species may be altered because of morphological changes induced by UV-B. Cereals and grasses will be more sensitive to this effect than broad leaved plants. vii) In certain species and varieties, UV-B exacerbates the effects of other environmental stressors such as drought and ozone. viii) Under conditions of elevated CO2, UV-B prevents the increases in CO2 consumption expected in wheat and rice. This means that current estimates of the effects of global warming on the environment may need to be reassessed. ix) The elevations in UV-B that will occur in the next decades may be too rapid for natural plant communities to be able to adapt. 8. References (Omitted here; unscannable) B. THE EFFECTS OF OZONE DEPLETION ON MARINE ORGANISMS (Omitted here; unscannable) C. THE EFFECT OF OZONE DEPLETION ON FARM ANIMAL SPECIES (Omitted here; unscannable)