How to recognize ozone symptoms

The following general guidelines can be given to identify ozone symptoms in plants (adapted from the Manual on Methods and Criteria for Harmonized Sampling, Assessment, Monitoring and Analysis of the Effects of Air Pollution on Forests Part X).

Symptom identification for broadleaf species

Visible ozone-like symptoms can be identified and distinguished from symptoms caused by other biotic/abiotic factors by following the general guide lines as described below:

· Symptoms are more severe on mid-aged and older leaves than on younger leaves. Older leaves are the first to develop symptoms (age effect).

Detail of a Sambucus ebulus plant fumigation with ozone in OTCs; only old leaves are affected (Photo: M.J. Sanz & V. Calatayud)

Ozone symptoms in Prunus spinosa fumigated in OTCs. Note that older leaves are more affected than younger ones (Photo: M.J. Sanz & V. Calatayud)

· Shaded portions of the leaves (i.e. if two leaves overlap) usually do not show any injury (shade effect).

Ozone symptoms (bronzing) in Fagus sylvatica near Torino, Italy. Note that shaded portions of leaves remain greener, less affected by ozone (Photo: M.J. Sanz & V. Calatayud).

· Visible ozone injury normally does not go through the leaf-tissue. Visible symptoms are most likely confined to the upper leaf surface, typically expressed as tiny purple-red, yellow or black spots (described as stipple) or sometimes as a general even discoloration, reddening or bronzing.

Severe ozone symptoms in Ulmus glabra in southern Switzerland. (Photo: M.J. Sanz & V. Calatayud)

Underside of the above leaf. Note than despite the severe injury in the upper side of the leaf, its lower side remain unaffected (Photo: M.J. Sanz & V. Calatayud)

· Both, stippling and even discoloration, only occur between the veins (interveinal) and do not affect the veins.

Ozone symptoms in Hibiscus syriacus fumigated in OTCs (Photo: V. Calatayud)

· Injured leaves appear to senesce faster and drop sooner.

Fumigation of Salix alba plants with enhanced ozone levels accelerated leaf senescence. In this picture: a senescent leaf (Photo: V. Calatayud)

Symptom identification for conifer species

Visible ozone and visible ozone-like symptoms for conifer species can be assessed by following the general guide lines as described below:

· Visible ozone and visible ozone-like symptoms for conifer species are expressed at the upper parts of the crown, on the upper side of the branches and needles.

· Chlorotic mottling is the most common symptom described for conifer needles; it is the result of chronic exposure to ozone and can be described as yellow or light green areas of similar size without sharp borders between green and yellow zones. However, not all needles in a fascicle may be uniformly affected.

· Chlorotic mottling frequently appears only in needles older than 1 year (second-year needles and older). That is, the observed symptom seems to increase with increasing needle age (age effect).

· Chlorotic mottling is more distinct on light-exposed needle areas in comparison to shaded ones.

· It is easier to observe the mottling, if several needles are held close to each other, forming a “plane” of needles.

Ozone symptoms in Pinus strobus from Torino (Photo: M.J. Sanz & V. Calatayud)

Last Updated on Tuesday, 12 May 2009 22:32