Ozone Plant Damage: How To Fix Ozone Damage In Garden Plants
By: Jackie Carroll
Ozone is an air pollutant that is essentially a very active form of oxygen. It forms when sunlight reacts with exhaust from internal combustion engines. Ozone damage to plants occurs when plant foliage absorbs ozone during transpiration, which is the plant’s normal breathing process. The ozone reacts with compounds inside the plant to produce toxins that affect the plant in a variety of ways. The result is reduced yields and unsightly discolorations, such as silver spots on plants.
How to Fix Ozone Damage
Plants under stress are most likely to be seriously affected by ozone damage, and they recover slowly. Treat injured plants by providing conditions as close to the ideal for the species as possible. Irrigate well, especially on hot days, and fertilize on schedule. Keep the garden weed-free so that the plants don’t have competition for moisture and nutrients.
Treating ozone injured plants won’t correct the damage that is already done, but it can help the plant produce new, healthy foliage and help prevent diseases and insects that normally attack weak and injured plants.
Ozone Plant Damage
There are a number of symptoms associated with ozone plant damage. Ozone first damages foliage that is almost mature. As it progresses, older and younger leaves may also sustain damage. The first symptoms are stippling or tiny spots on the surface of the leaves that may be light tan, yellow, red, red-brown, dark brown, black, or purple in color. Over time, the spots grow together to form large dead areas.
Here are some additional symptoms you may see in plants with ozone damage:
- You may see bleached out or silver spots on plants.
- Leaves may turn yellow, bronze, or red, inhibiting their ability to perform photosynthesis.
- Citrus and grape leaves may wither and drop off.
- Conifers may show yellow-brown mottling and tip burn. White pines are often stunted and yellow.
These symptoms closely mimic those of a variety of plant diseases. Your local cooperative extension agent can help you determine whether the symptoms are caused by ozone damage or disease.
Depending on the extent of the damage, plants may have reduced yields. Fruits and vegetables may be small because they mature too early. The plants will likely outgrow the damage if the symptoms are light.
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Read more about Environmental Problems
Air Pollution - Annuals, Bulbs, Groundcovers, Perennials and Vines
Bronzy leaf spots on Rudbeckia foliage
Air pollution damage is more common in urban areas but can also occur in suburban and rural areas downwind of industrial sites. The severity of plant damage caused by air pollution varies with the time of day and with environmental conditions such as heat, wind conditions, sunlight, and soil type. Ozone, PAN and Sulfur dioxide are common air pollutants.
Ozone injury in cucurbit crops
White to tan small spots on the leaves of the gourd Turk’s Turban in the following photographs are due to ozone. They were taken on 6 August 2004.
The interveinal necrotic (brown) tissue in the watermelon leaf below is the result of damage from exposure to high concentration of ozone.
Exposure to ozone caused the small, white spots on the pumpkin leaves in the following photographs. Sometimes part of a leaf blade is not injured due to stomates being closed.
In early August 2008 when ozone reached concentrations high enough to cause injury, plants generally were wilting under the hot and dry conditions then, consequently stomates were closed limiting ozone influx into leaves and thus very little damage was observed.
Margaret McGrath, Associate Professor
Long Island Horticultural Research & Extension Center
Riverhead, NY 11901-1098
Email: [email protected]
Every summer and fall, I hire research assistants to help me conduct my research. Interested? Contact me: [email protected]
Podcast: What’s wrong with my tomatoes?
Meg McGrath talked with Margaret Roach about tomato troubles on Roach’s popular A Way to Garden podcast.
Air Pollution Effects on Vegetables
The burning of coal and other fossil fuels gives rise to various chemical pollutants such as SO2 (sulfur dioxide), NOx (nitrogen oxides such as nitrite, nitrate, etc.), O3 (ozone) as well as a variety of other hydrocarbons. Ozone and peroxyacetyl nitrate (PAN) produced in these reactions can become injurious to plants depending on concentration and duration of exposure. Ozone causes up to 90 percent of the air pollution injury to vegetation in the United States and negatively influences plant growth and development causing decreases in yield. Ozone injury to watermelons is common in the mid-Atlantic area. After ozone, PAN is the next most phytotoxic air pollutant.
Movement of Pollutants into Plants
Most of the polluting gases enter leaves through stomata, following the same pathway as CO2. NOx dissolves in cells and gives rise to nitrite ions (NO2 – , which is toxic at high concentrations) and nitrate ions (NO3– that enter into the nitrogen metabolism of the plant as if they were absorbed by the roots). In some cases, exposure to pollution, particularly SO2, causes stomates to close, which protects the leaf against further entry of the pollutant but also stops photosynthesis. In the cells, SO2 dissolves to produce sulfite ions, which can be toxic, but at low concentrations they are effectively detoxified by the plant. SO2 air pollution can actually provide a sulfur source for the plant.
Tomato, watermelon, squash, potato, string beans, snap beans, pinto beans, tobacco, soybeans, cantaloupe, muskmelon, alfalfa, beets, sunflower, carrots, sweet corn, gourds, green peas, turnips, grapes, peaches, and strawberries are some of the more susceptible crops to air pollution damage. Cucumbers, pumpkins, and peppers are less susceptible. Watermelon and squash are the most sensitive of the cucurbits followed by cantaloupe.
Ozone: Ozone is considered the most damaging phytotoxic air pollutant in North America. Injury is most likely during hot, humid weather with stagnant air masses. Symptoms consist of small, irregular shaped spots or flecks that range in color from dark brown to black or light tan to white (Fig.1). Symptoms also include stipples (small darkly pigmented areas approximately 2-4 mm in diameter), bronzing, and reddening. These symptoms usually occur between the veins on the upper leaf surface of older and middle-aged leaves, but may also involve both leaf surfaces for some species and cultivars (Figs.1 and 2). The type and severity of injury depends on the duration and concentration of ozone exposure, weather conditions, and plant genetics. Some or all of the symptoms can occur on vegetables under various conditions.
Symptoms on one cultivar can differ from the symptoms on another. With continuing ozone exposure the symptoms of stippling, flecking, bronzing, and reddening are gradually replaced with chlorosis and necrosis (Figs. 2d and e). Early ozone foliar damage (Figs. 2b and c) can resemble severe spider mite injury. The presence of mites can be confirmed by examining the underside of the leaf. Mite populations would have to be comparatively great (>45/leaf) to cause the type of leaf injury shown in Figs.1b and c. As the exposure to ozone continues the spots may fuse forming larger necrotic areas (Figs. 2d and e). Due to the tissue collapse induced by ozone, leaves are prone to infection by pathogens such as Alternaria sp (early blight) and will senesce sooner. Plants that are exposed to high ozone concentrations metabolize less carbon dioxide, resulting in less carbon available for soil microbes to utilize. Consequently, soil enrichment and carbon processing decline resulting in decreased soil fertility. Symptoms of ozone damage can appear on one side of a plant or stem depending on the source of pollution and micro-climate (Fig. 3).
The injury pattern on the foliage is initially observed on older mature leaves near the crown or center of the plant, often progressing with time to the younger foliage. The yellowing of the plant centers in rows of watermelon is quite distinctive and can give fields an obviously striped pattern of alternating yellow and green bands.This type of injury on watermelon can be referred to as "center of the crown dieback." In contrast, injury on muskmelons is typically much less severe and is visible at a later stage of plant development. Irrigated plants will promote greater symptom development if the cultivar is sensitive compared with drought-stressed plants. Ozone injury on watermelons generally appears in mid to late July prior to fruit maturation. Ozone injury on beans appears as bronzing on the upper leaf surface and as the problem progresses necrotic lesions are formed that coalesce and become reddish brown.
Sulfur dioxide: Damage symptoms to crops caused by SO2 and its by-product sulfuric acid usually result in dry, papery blotches that are generally white, tan, or straw-colored and marginal or interveinal (Fig. 4). On some species, chronic injury causes brown to reddish brown or black blotches. Both the upper and lower leaf surfaces are affected. Leaf veins remain green. Young and middle-aged plants and leaves are most sensitive. Sensitivity is highest during days with bright sunlight and high relative humidity.
Peroxyacetyl nitrate (PAN): Causes a collapse of tissue on the lower leaf surface of most plants resulting in leaves that develop bands or blotches of glazed, bronzed or silvery areas (Fig. 5). The affected leaves usually senesce prematurely. On some plants, such as Pinto bean, tomato, and tobacco, the injury can occur through the entire width of the leaf blade. PAN is most toxic to small plants and younger leaves, but leaves just forming and starting to open and the most mature leaves are less susceptible to PAN injury. The formation of PAN is well documented on the west coast of the U.S., with injury occurring on vegetation all along the coast, however, little is known about the concentration of PAN in the eastern United States.
Nitrogen Oxides (NOs): These pollutants play a major role in the production of ozone. NOs are likely contributors to a number of environmental effects such as eutrophication in coastal waters like the Chesapeake Bay. Eutrophication occurs when bodies of water undergo an increase in nutrients that reduce the amount of oxygen in the water, thereby producing an environment that is unfavorable to animal life. It is estimated that 50 million pounds of nitrogen make it into the Chesapeake Bay through deposition of NOs onto the Bay’s watershed (Cerco and Noel, 2004).
Ethylene: Occurs in trace (C2H4) amounts in propane, gasoline and natural gas and is produced when these substances are burned. It also is present in wood and tobacco smoke. Ethylene pollution influences the activities of plant hormones and growth regulators, which affect developing tissues and normal organ development, without causing leaf-tissue damage. Injury to broad-leaf plants occurs as a downward curling of the leaves and shoots (epinasty), followed by a stunting of growth. In high tunnels, which burn propane, kerosene or use motors that burn gasoline, that have poor or no ventilation, even minute amounts of this pollutant can cause severe damage to tomatoes. Tomato plants exposed to ethylene can develop plant twisting, defoliation, and bloom drop.
Estimated yield losses: Estimating yield loss due to air pollutants in the field is difficult and only approximations are available. In a California study, ozone damage to crops caused the greatest yield losses (10-30%) in cantaloupe, grape, onion, and bean. Sorghum and lettuce yields were found to be mostly unaffected by exposure to ozone. Other research has shown that when average daily ozone concentrations reach >50 ppb (parts per billion) yields of vegetables can be reduced by 5-15%.
Management: While there is no treatment for ozone injury it may be possible to select certain cultivars that are more tolerant of air pollution compared with others. Little research has been done in this area however, a watermelon/ozone study by Holmes and Schultheis (2001) in North Carolina showed that seedless cultivars tended to be more tolerant of ozone damage than seeded cultivars. The top 10 least susceptible watermelon cultivars in descending order were: W5051, W5052, Millionaire, HMX913, EX4590339, Freedom, HMX8914, Revolution, Millenium, and TRI-X 313. The 10 most sensitive cultivars in ascending order were: SXW 5023, Variety 800, Stars-N-Stripes, Pinata LS, Athens, WX8, Regency, ACX 5411, Starbrite, and Variety 910.
Cerco, C. F. and M. R. Noel. 2004. The 2002 Chesapeake Bay Eutrophication Model. United States Environmental Protection Agency Region III. Chesapeake Bay Program Office U.S. Army Corps of Engineers Engineer Research & Development Center Environmental Laboratory EPA 903-R-04-004. Found at: The 2002 Chesapeake Bay Eutrophication Model
Delucchi, M. A., J. J. Murphy, D. R. McCubbin, H. J. Kim. 1998. The Cost of Crop Damage Caused by Ozone Air Pollution from Motor Vehicles: Report #12 in the series: The Annualized Social Cost of Motor-Vehicle Use in the United States, Based on 1990-1991 Data. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-96-03(12).
Fiscus, E.L., Booker, F.L., Burkey, K.O. 2005. Crop responses to ozone: uptake, modes of action, carbon assimilation and partitioning. Plant, Cell and Environment 28:997.
Heagle, A.S. 1989. Ozone and crop yield. Annual Review of Phytopathology 27:397-423.
Holmes, G. J. and J. R. Schultheis. 2001. Susceptibility of watermelon cultigens to ozone injury. B&C Tests. vol. 109:1-2. Figures. 1 and 2 contributed by Gerald Holmes, NCSU.
Queen’s Printer for Ontario, 1991. Reproduced with Permission. Figures 3, 4 and 5.
Sikora, E. and A. H. Chappelka. 2004. Air Pollution Damage to Plants. ANR-913 The Alabama Cooperative Extension System.
What is ozone therapy? Benefits and risks
Ozone therapy is a controversial alternative medicine practice that uses ozone gas to fight disease.
Ozone is a form of oxygen. In alternative medicine, practitioners of ozone therapy use gas or liquid forms of ozone to treat medical conditions and as a topical disinfectant.
People have practiced ozone therapy in medical contexts for many years. However, its use is now controversial amid safety concerns.
In 2019, the Food and Drug Administration (FDA) warned against using ozone therapy. This is because there is not enough evidence to conclude that it is effective or safe for medical use.
This article provides an overview of ozone therapy, including its uses, proposed benefits, and possible risks and side effects.
Share on Pinterest Some health organizations, including the FDA, have concerns about the safety of ozone therapy.
Image credit: James Mutter, 2015.
Ozone therapy refers to medical practices that use ozone gas.
Ozone gas is a form of oxygen. This colorless gas is made up of three oxygen atoms. In the upper atmosphere, a layer of ozone gas protects the earth from the sun’s UV radiation. On ground level, however, ozone is “a harmful air pollutant.”
Ozone gas is harmful when a person inhales it, leading to lung and throat irritation, coughing, and worsened asthma symptoms. High exposure can lead to lung damage and can be fatal.
However, some researchers believe that ozone can have therapeutic effects in medical contexts. For example, one 2011 review reports that ozone therapy has had the following uses:
- treating arthritis
- fighting viral diseases, such as HIV and SARS
- disinfecting wounds
- activating the immune system
- treating ischemic heart disease
- treating macular degeneration
- treating cancer
Researchers are currently exploring the effects of ozone therapy on the human body to identify any potential therapeutic benefits.
So far, however, there has been little research into the true effectiveness and safety of ozone therapy. For this reason, official organizations do not currently approve its use.
According to one 2005 report, there is not enough evidence to recommend ozone therapy for HIV or other infectious diseases, heart disease, cancers, skin conditions, or a range of other conditions.
Although ozone has shown success against the virus that causes HIV outside the body, no research to date has shown its safety or effectiveness in live humans.
Some research suggests that ozone therapy can fight disease, including cancer, by modulating the immune system response and reversing oxygen deficits in the body.
However, Complementary and Alternative Medicine for Cancer (CAM Cancer) state that there have been no randomized controlled trials in people with cancer and very few human trials of ozone therapy for any condition.
The FDA do not authorize the use of ozone “[i]n any medical condition for which there is no proof of safety and effectiveness.”
This means that researchers need to run many more trials before determining the true effects of ozone therapy on the human body and whether or not it has any therapeutic benefits.
4 Reasons Why You Should Avoid Air Purifiers that Produce Ozone
Not only is ozone potentially dangerous to your health, it may not even work at all. Below are four reasons why you should never use an air purifier that produces ozone.
1. Ozone Generators May Not Work at All
Some manufacturers suggest that ozone will render nearly every chemical contaminant in the home harmless by producing a chemical reaction. This is incredibly misleading because a thorough review of scientific research has shown that in order for many of the dangerous chemicals found indoors to be eliminated the chemical reaction process may take months or even years. Other studies have also (PDF) noted that ozone cannot effectively remove carbon monoxide or from outside. If used at concentrations that do not exceed public health standards, ozone applied to indoor air pollution does not effectively remove viruses, mold, bacteria, or other biological pollutants.
2. The Chemical Reaction Can Be Dangerous
Even if ozone generators were proven to be effective at eliminating these chemicals, there are certain side effects everyone must be aware of. Many of the chemicals ozone reacts to results in a variety of harmful by-products. For example, when ozone was mixed with chemicals from new carpet in a laboratory setting, the ozone reduced many of the chemicals but created a variety of dangerous organic chemicals in the air. While the target chemicals were reduced, the dangerous byproducts rendered the process moved.
3. Ozone Generators Do Not Remove Particulates
A third factor to consider when looking at ozone generators is that they do not remove particulates such as dust or pollen from the air. This includes the particles which are primarily responsible for allergic reactions. To combat this, some ozone generators include an ionizer which disperses negatively charged ions into the air. In recent analysis’s, this process was found to be less competent in the removal of air-borne molecules of dust, smoke, pollen, and mold spores than HEPA filters and electrostatic precipitators.
4. It Is Impossible to Predict Exposure Levels
The EPA notes that it is increasingly difficult to determine the actual concentration of ozone produced by an ozone generator because so many different factors come into play. Concentrations will be higher if more powerful devices used in smaller spaces. Whether or not the interior doors are closed rather than open will affect concentrations as well. Additional factors which affect concentration levels include how many materials and furnishings are in the room to react with ozone, the level of outdoor air ventilation, and the proximity of a person to the ozone generating device.
Exposure of plants to high levels of ozone has been shown to alter the interactions between plants and insect herbivores. However, the duration of the exposure and interactions with ambient temperature have not yet been considered as factors affecting plant-herbivore interactions. In this study, longer exposures to ozone affected the quality of Sinapis arvensis plants more strongly, with subsequent stronger effects on the interactions with the herbivore Pieris brassicae. P. brassicae butterflies avoided ozone exposed plants for oviposition. Despite a positive effect of ozone exposure on the survival of the eggs, the number of hatched caterpillars was lower on ozone-exposed plants and the caterpillars performed less well when feeding on them, particularly at higher ambient temperatures, a climate scenario that is likely to become more common in the future.
Increasing the duration of exposure of S. arvensis plants to ozone resulted in avoidance of these plants by P. brassicae butterflies when choosing oviposition sites. This is likely due to alterations in the chemical cues produced by the plant, particularly changes in the chemicals of the leaf boundary layer, that are often used in food plant acceptance 30 . Our study is in accordance with some other studies addressing the plant-mediated effects of ozone on the oviposition preference of insect herbivores that show that the insects prefer to lay eggs on control plants 6,36 . In other studies, exposure of the plant to ozone had no effect on oviposition preference 11,35 , but, as we observed in the present study, this could be a matter of duration of exposure. In studies where the plants were presented to the insects during the exposure, some insects had a preference for laying eggs on control plants 37 whilst others preferred ozone-exposed plants 35 .
Plants may react to egg deposition by a hypersensitive response 32 . In our study, the survival of the eggs was positively affected by ozone. We hypothesize that the exposure to an abiotic stress (ozone) prior to egg deposition may have inhibited a defence response from the plant in ozone-exposed plants, leading to a positive effect of ozone in the egg survival rate. Griese et al. 53 showed that the expression or severity of the hypersensitive response does not increase with an increased number of eggs laid, but single-laid eggs are more susceptible to it than eggs laid in clusters and eggs laid in smaller clusters have a tendency to be more susceptible than eggs laid in bigger clusters. This is presumably because they are more vulnerable to desiccation. Although we did not specifically register survival per cluster, there was a positive correlation between the number of eggs per plant and the average number of eggs per cluster (r = 0.75). We consider that an increased susceptibility of eggs in smaller clusters to a defence response may be the reason why, in this study, the egg survival rate was higher on plants with more eggs laid on them. Despite the positive effect of ozone on egg survival, the number of caterpillars per plant after hatching was still higher for control plants than for ozone-exposed plants, showing an overall negative effect of ozone.
The effect of ozone on caterpillar performance was also negative, but only for longer exposures and only when the caterpillars were reared at higher ambient temperatures. This gives rise to two non mutually exclusive hypothesis: (1) higher temperatures intensify the response of the plants to ozone with consequences to their nutritional value and/or to their level of toxicity, therefore affecting the caterpillars development or (2) higher temperatures increase the metabolic rate of the caterpillars, leading caterpillars that have similar weights at hatching to diverge faster, and therefore to show an indirect response to ozone. In any of these cases, the lower weight of caterpillars reared on plants exposed to ozone for 5 days may mean that the caterpillars are growing into lighter, weaker pupae or that the caterpillars will take longer to pupate, and therefore that their life cycle will be extended. The latter was the case in a study by Jondrup et al. 39 , where they observed that caterpillars reared on ozone-sensitive plants exposed to ozone reached the same final weight, but took longer to pupate than the caterpillars reared on the control plants. On the other hand, Couture et al. 10 observed that caterpillars showed decreased growth when fed foliage from trees growing under elevated ozone conditions. In Khaling et al. 5 both phenomena occurred: caterpillars reared on ozone-exposed plants took longer to pupate and the pupae were lighter. If the reduced weight of the caterpillars reared on ozone-exposed plants shown here, translate into a longer caterpillar stage, together with the fact that the egg stage was also longer for eggs laid on ozone-exposed plants, the herbivores will have longer life cycles. Consequently, the number of generations produced per year may decrease and the predation or parasitism risk during the developmental stage may increase. Plant-mediated effects of ozone on caterpillar performance are not globally negative: Bolsinger et al. 38 showed a higher relative growth rate of caterpillars when reared on plants exposed to ozone and Jackson et al. 27 observed a tendency for increased growth of caterpillars fed with plants grown under elevated ozone conditions. Kopper et al. 54 observed that ozone had no effect on the performance of caterpillars reared on trees growing under elevated ozone conditions and Jondrup et al. 39 also saw no effect of ozone on caterpillars reared on resistant and wild type lines. When coupled with information about the nutritional state of the host, some studies suggest that alterations in caterpillar weight are related to changes in the nitrogen content of the host’s leaves, whether the effect of ozone was negative 5,9,10,12 or positive 27 . Interestingly, in no-choice tests, caterpillars either consumed similar amounts of plant material irrespective of plant treatment 39 or consumed more ozone-exposed plant material than control plant material 14,36 , which could indicate a mechanism to compensate for the reduction in nutritional value. However, in dual-choice feeding tests, herbivores also consumed more ozone-exposed plant material 3,5 suggesting that changes in palatability may be the reason for the modified consumption.
In this study, the butterflies laid more eggs on control plants than on ozone-exposed plants, the same plants that later led to a better caterpillar performance. This is in agreement with the preference-performance hypothesis 55 which states that females choose oviposition sites that maximize the fitness of their offspring. By doing so, and having fairly mobile adults, P. brassicae may be able to escape the detrimental effects of ozone on its development as long as small scale variability in ozone damage exists. On the other hand, not being able to move, plants cannot escape ozone. They suffer stress from both ozone exposure and herbivory. We did not test for feeding preferences, but if Khaling et al. 5 ’s results on the increased consumption of ozone-exposed plant material would be applied in this situation, the fact that, as we observed, ozone-exposed plants had fewer caterpillars on them after hatching, may not be enough to compensate for the increased consumption. In our case ozone exposure seems to be a bad deal for both the plant and the herbivore. But even if one of them would be favoured by the exposure, the alterations in plant-herbivore interactions may affect the organisation of food webs, disturbing the balance of ecosystems.
Overall, the direction and strength of the herbivore response to ozone-exposed plants seem to vary between plant-insect systems. This variability may be caused by (1) different sensitivity to ozone between plant species, varieties or growth stages, (2) different susceptibility of the herbivores to the changes that ozone triggers in the plant or (3) different ozone exposure levels tested. The degree of sensitivity of a plant to ozone determines the exposure level that causes measurable changes in the plant which modify the plant’s interaction with its herbivores. In this study, both the plant and the herbivore were sensitive enough so that ozone effects could be observed on the herbivore life cycle at the ozone levels studied. Our results also suggest that the effects of ozone on plant-insect interactions are cumulative, since ozone affected oviposition and caterpillar performance when the plants were exposed for 5 days but not when plants were exposed for 1 day. However, Agathokleous et al. 56 proposed that a plant does not respond linearly to ozone. A plant’s response to ozone could also follow a hormetic model, with low doses being beneficial to plants and detrimental effects only being observed when the ozone dose exceeds the NOAEL (no-observed-adverse-effects level). In the present study, the detrimental effects on plant-insect interactions observed for an exposure of 120 ppb ozone, 6 h/day for 5 days reveals that this level of ozone is beyond the NOAEL for this plant-herbivore system.
Our results identify that relatively low concentrations of ozone affect plant-herbivore interactions. AOT40 (Accumulated Ozone exposure over a Threshold of 40 ppb) is an index defined by the European Union (EU) for the protection of the vegetation. It is determined by calculating the sum of the difference between hourly concentrations greater than 40 ppb and 40 ppb over a given period using hourly values measured between 8 h 00 and 20 h 00 CET. In the Directive on Ambient Air Quality 57 , the EU pointed to 6000 µg/m3.h (
3000 ppb.h) as the long-term objective to be reached. In our 5-day-long treatments, the calculated AOT40 is
2300 ppb.h, a level well below EU’s objective. However, as our results show, this level of exposure was already enough to cause damaging effects on the plants (visible injury) as well as to affect plant-herbivore interactions (oviposition and caterpillar performance). This points to the need of reviewing the European legislation on air quality, because currently it does not account for the damaging effect of acute ozone exposure, that seems to be important at least for annual plants like the one we used. Importantly, our data indicate that more frequent ozone peaks combined with higher temperatures, as predicted for a future with ongoing global warming and environmental pollution, will reinforce the negative effects of ozone on plant-herbivore interactions.
In summary, we showed that exposing S. arvensis to ozone affects several parameters of the life cycle of its herbivore P. brassicae. Our results reveal that a more severe exposure to ozone, especially when combined with higher temperatures, strengthens the effects of the pollutant on plant-herbivore interactions. Because plants vary in their sensitivity to ozone and herbivores vary in their susceptibility to changes in the plants, the alterations in plant-herbivore interations may vary in strength and direction between plant-herbivore systems, affecting the organisation of food webs and possibly disturbing the balance of ecosystems. This accentuates the need to implement measures to reduce the emission of precusors that could lead to ozone peaks such as the ones tested here, particularly in parts of the world where the use of fossil fuels is still increasing.