TEMPORAL DEVELOPMENT OF VISUAL OZONE INJURY ON THE FOLIAGE OF PRUNUS-SEROTINA - A STATISTICAL EVALUATION

Ozone-induced visible injury to plants is relatively common in North A merica but has rarely been reported in Europe. The south of Switzerlan d (canton Ticino) has been identified as having high ambient ozone exp osures relative to other parts of Switzerland, with accumulated annual exposures over a threshold of 40 ppb (40 nl O-3 litre(-1)) for daylig ht hours from April to September of > 30 ppm x h. Ozone-induced foliar injury on black cherry (Prunus serotina) has been observed in the are a. The main purpose of this study was to establish whether seedlings o f black cherry grown in three different treatments (open plots [ambien t ozone concentrations], chambers receiving non-filtered [96% ambient] air and charcoal-filtered chambers [ca. 60% ambient]) showed signific ant differences with respect to the various aspects of ozone injury de velopment, particularly trends in injury development, the survival pro babilities, the average injury level of a tree and the proportion of t rees showing any sign of injury over the summer growing season. Visual estimates of the percentage of leaves showing symptoms (adaxial stipp le and leaf reddening) on a plant and the percentage of leaf area of o nly the injured leaves which showed symptoms of ozone injury were reco rded weekly for each seedling for eight consecutive weeks. These two s cores were multiplied to derive a measure of injury (Y) which can be i nterpreted as the proportion of injured leaf area on a tree. This deri ved score was used in all subsequent analyses. In this paper we assess whether, overall, an increasing trend in the injury levels, as given by the values of Y, was evident. We have also estimated the probabilit y F(t) that the first sign of injury (measured by Y) might occur after a given number t of weeks. The smaller the value of F(t) for a given t, the stronger the effect of the treatment (i.e. the treatment causes relatively more damage). The average injury level of a tree and the p roportion of trees that showed any sign of injury over the 8-week peri od were also analysed. The results from the open plots, the non-filter ed chambers and the charcoal-filtered chambers were significantly diff erent. However, no statistically significant difference was found betw een the open plots and the non-filtered chambers. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.