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Welcome to the search site of the LWF Ozone Website!

The LWF Ozone Website is based on a continuously updated databank and, therefore, searchable for various criteria such as plant form, species, country, region, and project in which the symptom was found, and the form of the validated or non-validated symptom. After some short instructions for an efficient search, explanations and comments for the search criteria are following. The section with important guidelines for the diagnosis of ozone-induced injury is summarized by a flow chart for the field.

 
Instructions This is how it works: For each search criteria, you choose a specific plant form, plant species, country, etc. Note: For 'Plant species', 'Country', and 'Symptom Form' there are multiple choices possible. By holding down the Ctrl key you are able to make more than one selection for the respective criteria. After making your selection, start your search with the 'Search' button. You can always change your prior selction in the frame without going back or resetting your search. To get back to the default setting, i.e. all possibilities, you highlight the 'Reset' button. Note: Contradicting combinations may be possible.
 
Explanations and comments for the search criteria
 
Plant Form
  Tree: A woody perennial plant having a single usually elongated main stem with generally few or no branches on its lower part.
  Shrub: A low, usually several-stemmed woody perennial plant growing up to 5 m in born height and branches from the bottom.
  Herb: A seed-producing annual, biennial, or perennial plant that does not develop persistent woody tissue but dies down at the end of growing season.
  Crop: A plant (or animal) that can be grown and harvested extensively for profit or subsistence.
 
Plant Species Note: Multiple selection is possible with Ctrl.
There are currently 14 symptomatic plant species included in the data bank. Each species is listed with one to several different symptom descriptions.
 
Country Note: Multiple selection is possible with Ctrl.
It is the aim to collect information about ozone visible injury from as many countries as possible where plants develop visible symptoms in response to elevated ozone exposures. Each registered country is divided into regions where ozone symptoms were found.
 
Symptom Forms Note: Multiple selection is possible with Ctrl.
Ozone causes several general symptoms on broadleaf species in the field, the most common of which is stipple, or pigmentation. As a general rule in aiding diagnosis, ozone injury is expressed as an upper leaf surface stipple (lower surface clean of symptoms), with no stippling on the veins or veinlets, and with leaves towards the base of twigs (older leaves) showing increasing degrees of stippling, general leaf discoloration or chlorosis, and early senescence, possibly followed by necrosis as the growing season, and therefore exposures to ambient ozone concentrations continue (Innes et al., 2001).
  Chlorosis: In many species, the development of stippling is followed by loss of chlorophyll from the leaves, resulting in the development of chlorosis (yellowing or paling of normally green plant tissue), especially in the case of older leaves. The development of chlorosis and subsequent leaf fall is a normal part of the autumnal senescence process. As a result, considerable care is needed in the timing of any assessment of foliar injury on numerous ozone-sensitive plant species (Innes et al., 2001).
  Early senescence: Early decline or degeneration of tissue, plant parts, or plants that occurs between maturity and death; can be accelerated by disease or stress (Flagler et al., 1998).
  Even discoloration: The upper leaf surface of plants may have a tan, red, brown, purple, or black coloration that appears at first glance as being uniformly distributed over the leaf surface. Closer examination with a hand lens will reveal that affected areas are restricted to certain areas of the leaf, or appear as discrete, dot-like areas of increased pigmentation, called stippling. Veins and veinlets are usually not involved, and veinlets consistently bound the injury areas producing angular sections of affected cells and tissues. In some species young foliage has a reddish discoloration on the upper surface of the foliage. This is not caused by ozone and is usually easily distinguished from ozone-induced injury as it is normally the oldest foliage that shows the highest amounts of ozone-induced injury due to longer periods of exposures throughout the duration of the summer oxidant season (Innes et al., 2001).
  Necrosis: Death of cells or plant parts, usually resulting in the tissue turning brown or black due to oxidation of phenolics (Flagler et al., 1998).
  Stipple: Stippling is best observed by holding the leaf toward the sun while looking for very small, pepper-like, darkened interveinal areas of affected tissues. The stippling is often restricted to sun-exposed parts of leaves; the presence of another leaf directly overlapping a leaf may prevent symptoms from developing on the overlapped part (shading effect). Stippling has been described as the most definitive symptom of ozone injury on broadleaf species. The coloration of stippling is usually characteristic for a species but can vary with environmental or physiological conditions; dark red, reddish purple, and darker brown/black coloration is most common. On young leaves symptoms tend to develop at the leaf margins and tips; on older leaves symptoms develop first toward the base. In the late summer and early autumn, the entire surface of older leaves may exhibit symptoms following season-long exposures to ozone. Stippling is distinguishable from spotting since the discoloration is on the upper surfaces of the leaves only and does not extend across veins or veinlets (Innes et al., 2001).
 
Status To be able to provide a quality assurance for the LWF Ozone Website we introduced the search criteria 'Status'. The status indicates whether the symptom is validated or not validated. We determined a symptom as validated
  1. if the finding is published or
  2. if the symptom went through the validation process of one of the three ICP-Forests Validation Centres for the Assessment of Ozone Injury.
You may find symptoms under the status 'non-validated' which are typical ozone-induced injury but have not yet been validated.
 
Projects The purpose of this search criteria is to provide some information about the project methods and the environmental conditions under which the symptom has been found. This list may be extended as more countries with differing programs will join. Currently, the following project methods are listed:
  CSTR Continuously-Stirred Tank Reactor; a growth chamber for plants where environmental factors such as light, relative humidity, temperature, mixture of ambient air and air pollutant, etc. can be controlled and stirred.
  Level I For monitoring forest condition and its spatial and temporal changes on a large scale over a necessary period of time, the so-called Level I network has been established. The Level I system covers the main forests in Europe adequately. The Level I network consists of approximately 6,000 monitoring plots, which are systematically arranged in nominal grid throughout Europe. In addition, several countries are executing surveys at a denser national grid net in order to obtain reliable estimates at national and regional levels.
  Level II For the intensive monitoring program (Level II) more than 860 permanent observation plots have been established with the aim of investigating key factors and processes at the ecosystem scale. Plots have been selected in such a way that major forest ecosystems are represented following general recommendations by ICP Forests.
  OTC The so-called open-top chambers follow the design and specifications developed by Allan Heagle. OTC's are chambers with transparent side-walls and open tops through which either ambient air (100% O3) or charcoal filtered air (50% O3) is continually pumped. Through the open top and the continuos wind flow, the environmental conditions inside the chambers can be considered as 'close to natural'.
  Others Any symptoms which were found within a non-specific or a not listed project.
 
Diagnosis (From Innes et al., 2001).
Some degree of expertise is required to recognize ozone-induced foliar symptoms. It may be confusing to distinguish ozone-induced symptoms from symptoms caused by other biotic or abiotic stressors such as insects, fungi and viruses, heat, drought, or nutrient deficiency. Although the coloration of ozone-induced stippling or general upper surface pigmentation is species specific and can vary with environmental and/or physiological conditions, several distinctive symptom characteristics can be observed when diagnosing ozone-induced injury.

To understand the characteristics of ozone-induced injury we have to keep in mind that foliar injury is a visible manifestation of internal physiological events that have taken place within the foliage. For example, many studies have shown that stomatal conductance and pollutant uptake, i.e. the rate with which a gas may enter a leaf, can be the main physiological event controlling the expression of visible ozone-induced injury. Knowing that stomatal conductance or ozone uptake are sensitive to various environmental factors such as light, relative humidity, soil water content and air temperature helps us to recognize characteristic patterns of the development of ozone-induced injury. Indeed, older leaves are usually more affected by ozone-induced injury than younger leaves due to longer durations of season-long exposures and higher cumulative ozone uptake (age effect). Or, an overlapping leaf may protect a portion of a lower leaf from ozone exposure and injury development by reducing the available amount of light and lessening the stomatal ozone uptake (shade effect).

As a set of general diagnostic features, ozone-induced injury is usually expressed as a dark colored (brown to reddish purple), upper leaf surface stipple (smaller than 1 mm) or as an upper surface general pigmentation (bronzing or reddening discoloration) with the lower leaf surface clear of symptoms; symptoms are not present on the veins or veinlets. Leaves towards the base of the twigs (older leaves) exhibit an increasing presence of stippling due to longer seasonal ozone exposures and higher cumulative ozone uptake. Additional possible diagnostic features are shading effects and premature leaf senescence followed by early leaf abscission.

The discussed diagnostic features may be summarized in a flow chart as a tool for the diagnosis of ozone-induced visible injury on broad leaf species. This flow chart is intended to help as a guide for the diagnosis of possible ozone-induced injury on broad leaf species. It is not exhaustive and further research may reveal more symptomatic plant species and a wider range of symptoms.