Ozone pollution and ozone biomonitoring in European cities Part II. Ozone-induced plant injury and its relationship with descriptors of ozone pollution

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Atmospheric Environment 40 (2006) 7437–7448 www.elsevier.com/locate/atmosenv

Ozone pollution and ozone biomonitoring in European cities Part II. Ozone-induced plant injury and its relationship with descriptors of ozone pollution Andreas Klumppa,, Wolfgang Ansela, Gabriele Klumppa, Phillippe Vergneb, Nicolas Sifakisc, Marı´ a Jose´ Sanzd, Stine Rasmussene, Helge Ro-Poulsene, A`ngela Ribasf, Josep Pen˜uelasf, Harry Kambezidisc, Shang Heg,1, Jean Pierre Garrecg, Vicent Calatayudd a

Institute for Landscape and Plant Ecology and Life Science Center, University of Hohenheim, 70599 Stuttgart, Germany b ENS Lyon and Lyon Botanical Garden, 46 Allee d’Italie, 69364 Lyon Cedex 07, France c Institute for Space Applications & Remote Sensing and Institute of Environmental Research & Sustainable Development, National Observatory of Athens (NOA), P.O. Box 20048, 11810 Athens, Greece d Fundacio´n CEAM, Parque Tecnolo´gico, c/ Charles Darwin 14, 46980 Paterna (Valencia), Spain e Botanical Institute, University of Copenhagen, Øster Farimagsgade 2D, 1353 Copenhagen K, Denmark f Unitat d’Ecofisiologia CSIC-CEAB-CREAF, CREAF (Centre de Recerca Ecolo`gica i Aplicacions Forestals), Universitat Auto`noma de Barcelona, 08193 Bellaterra (Barcelona), Spain g INRA Nancy, Laboratoire Pollution Atmosphe´rique, 54280 Champenoux, France Received 16 December 2005; received in revised form 4 July 2006; accepted 4 July 2006

Abstract Within the scope of a biomonitoring study conducted in twelve urban agglomerations in eight European countries, the ozone-sensitive bioindicator plant Nicotiana tabacum cv. Bel-W3 was employed in order to assess the occurrence of phytotoxic ozone effects at urban, suburban, rural and traffic-exposed sites. The tobacco plants were exposed to ambient air for biweekly periods at up to 100 biomonitoring sites from 2000 to 2002. Special emphasis was placed upon methodological standardisation of plant cultivation, field exposure and injury assessment. Ozone-induced leaf injury showed a clearly increasing gradient from northern and northwestern Europe to central and southern European locations. The strongest ozone impact occurred at the exposure sites in Lyon and Barcelona, while in Edinburgh, Sheffield, Copenhagen and Du¨sseldorf only weak to moderate ozone effects were registered. Between-site differences within local networks were relatively small, but seasonal and inter-annual differences were strong due to the variability of meteorological conditions and related ozone concentrations. The 2001 data revealed a significant relationship between foliar injury degree and various descriptors of ozone pollution such as mean value, AOT20 and AOT40. Examining individual sites of the local monitoring networks separately, however, yielded noticeable differences. Some sites showed no association between ozone pollution and ozone-induced effects, whereas others featured almost linear relationships. This is because the actual ozone flux into the leaf, which is modified by Corresponding author. Tel.: +49 711 4593043; fax: +49 711 4593044.

E-mail address: [email protected] (A. Klumpp). Present address: Chinese Academy of Forestry, Research Institute of Forest Ecology and Environmental Science, Wan Shou Shan, Beijing 100091, PR China. 1

1352-2310/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2006.07.001

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various environmental factors, rather than ambient ozone concentration determines the effects on plants. The advantage of sensitive bioindicators like tobacco Bel-W3 is that the impact of the effectively absorbed ozone dose can directly be measured. r 2006 Elsevier Ltd. All rights reserved. Keywords: Air quality; Bioindicators; Tobacco Bel-W3; AOT40; Urban air pollution

1. Introduction Tropospheric ozone is an air pollutant of major concern on both the European and global scale, with current concentrations being high enough to harm human health, agricultural productivity and biodiversity over wide areas. Recently established target values and long-term objectives for the protection of human health and vegetation (EU (European Union), 2002) are frequently being exceeded in large regions of Europe, including urban agglomerations in many countries (EEA (European Environment Agency), 2003). Ozone concentrations and doses in various regions and cities reveal a strong spatial and temporal variability, with a clear north–south gradient and a significant differentiation between rural, suburban and urban sites within a given region or municipal area. This reflects different climatic conditions and emission sources of precursor substances (Sanz et al., 2004; Klumpp et al., 2006). Strong efforts are being made to reduce ozone pollution, e.g., by cutting down precursor emissions from traffic and industrial sources based on agreements established by the Gothenburg Protocol (UNECE (United Nations Economic Commission for Europe), 1999) and the NEC Directive (EU (European Union), 2001). Observations and projections point at a positive response to these measures: peak concentrations are declining, but global and supra-regional developments apparently provoke a gradual increase of global or hemispheric background values. This indicates that tropospheric ozone will remain on the environmental agenda in the future (Prather et al., 2003; Grennfelt, 2004; Vingarzan, 2004; Ashmore, 2005). Air quality control fundamentally aims at verifying whether compliance with the target or limit values set by national laws and European directives actually avoids harmful effects on humans and the environment. Biomonitoring using accumulative or sensitive indicator plants is an appropriate means to detect and monitor air pollution effects because bioindicators react to the biologically active pro-

portion of air pollution; they therefore display the integrated response of past and present environmental conditions. The extremely ozone-sensitive tobacco (Nicotiana tabacum L.) cultivar Bel-W3 has been used in numerous biomonitoring studies worldwide for more than four decades (Heggestad, 1991; Mulgrew and Williams, 2000). The different methods applied concerning plant cultivation, age and developmental stage of indicator plants, exposure duration, injury assessment, etc. have compromised the comparability of previous results (Heggestad, 1991; Toncelli and Lorenzini, 1999; Cuny et al., 2004; Saitanis et al., 2004; among others). A strict standardisation of methods is required to overcome the relatively poor comparability of data and the low acceptance of this biological monitoring procedure by regulators and policy makers. The first such national initiatives were taken in Germany starting in the 1990s (VDI (Verein Deutscher Ingenieure), 2003). In 1999, EuroBionet, the ‘European Network for the Assessment of Air Quality by the Use of Bioindicator Plants’, was established as a network of research institutes and municipal environmental authorities from twelve urban agglomerations in eight EU Member States. It aimed at promoting environmental awareness of the urban population and at assessing and evaluating air quality using highly standardised bioindication methods. Among various techniques, the ozone-sensitive tobacco cultivar Bel-W3 was employed to assess the occurrence of phytotoxic ozone effects at urban, suburban, rural and traffic-exposed sites. The present paper reports on the results of standardised exposure of tobacco plants at up to 100 biomonitoring sites in urban agglomerations during three years. These experiments were a first field test of the standardised method of tobacco exposure in such a large geographical area. The detailed analysis of foliar injury on exposed tobacco plants focuses on the 2001 data which are the most complete. We present the intensity as well as spatial and temporal variability of ozone-induced injuries and explore the relationship between

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2. Material and methods

various bioindicator species were exposed to ambient air in order to assess the effects of ozone, sulphurous compounds, metals, hydrocarbons and mutagenic substances (Klumpp et al., 2002, 2004).

2.1. The EuroBionet programme

2.3. Cultivation and exposure of tobacco plants

The present study was part of the European bioindicator programme EuroBionet (www. eurobionet.com), which aimed at assessing and evaluating air quality in twelve urban agglomerations throughout Europe using various bioindicator species from 2000 to 2002 (Klumpp et al., 2002, 2004). To this end, a network of municipal administrations and research institutes was established under the coordination of the University of Hohenheim. The project started in 1999 with the following cities and regions as participants: Copenhagen (Denmark), Edinburgh (UK), Klagenfurt (Austria), Greater Lyon (France), Sheffield (UK), and Verona (Italy). The City of Du¨sseldorf (Germany), the City of Ditzingen/Greater Stuttgart (Germany), Greater Nancy (France) and the regional government of Catalonia/Barcelona (Spain) joined the network in 2000, and the cities of Valencia (Spain) and Glyfada/Greater Athens (Greece) in 2001 (cp. Klumpp et al., 2006).

Seeds of the ozone-sensitive tobacco cultivar BelW3 were obtained from the State Institute for Crop Production (Landesanstalt fu¨r Pflanzenbau, Rheinstetten, Germany). The plants were cultivated between April and September each year in the local greenhouses of the partner cities using a mixture of commercially available, standardised soil type ED73 and river sand (8:1 by volume), plastic pots (1.5 L) and a semi-automatic watering system made of glass fibre wicks and water containers. The procedure largely corresponded to a method described in a draft version of the guideline of the German Association of Engineers (VDI, 2003). All material necessary for plant cultivation and field exposure was distributed to the local teams by the coordination office in order to ensure a high level of methodological standardisation. Plants with six fully expanded leaves were selected for exposure. Since cultivation in filtered air was not usually possible in the greenhouses, the plants were checked prior to exposure for leaf injury that may have been caused by elevated ozone concentrations during cultivation. Such values were considered in the final plant assessment after the two-week exposure period. Per site and series, four–six plants were exposed to ambient air in exposure racks (exposure height 90 cm, frame height 180 cm) as originally described by Arndt et al. (1985). Each rack was covered with green shading fabric (50%) on the top and at three sides and remained open towards the northern side. During outdoor exposure, plants were irrigated by the above system of suction wicks hanging into water reservoirs. The exposure duration was 1471 days. Thus, up to eight exposure series were carried out between late May and mid-September.

ambient ozone levels and ozone-induced effects on indicator plants.

2.2. Local networks In each city, local bioindicator networks with 8–10 exposure sites were implemented, including one or two reference sites with low levels of primary air pollutants as well as urban, suburban, industrial and traffic-exposed sites. Overall, about 100 bioindicator stations were established and operated during up to three years. Various criteria were considered when selecting the monitoring sites. The first was a relatively uniform distribution over the city area to best represent the pollution burden of the conurbation. Proximity to existing air monitoring stations, protection from theft and vandalism, and city planning matters also played an important role. The ‘Stuttgart’ monitoring network did not include biomonitoring sites in the city centre but three sites in the network’s associate partner, the township of Ditzingen northwest of the Stuttgart/ Middle Neckar conurbation, as well as four sites on the university campus and in three municipalities in the Neckar valley southeast of Stuttgart. They were run directly by the coordination team and were treated as one common network. At all the sites,

2.4. Visual injury assessment After the two-week exposure period, the tobacco plants were exchanged with a new set and the ozone-induced plant injury on three reference leaves (leaves no. four–six) was recorded as percentage of damaged leaf area in relation to whole leaf area. The visual assessment of damaged leaf area was

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Table 1 Five-stepped scale for classifying ozone effects on tobacco plants Ozone impact

Very weak

Weak

Medium

Strong

Very strong

Damage class Leaf injury (%)

1 0−5

2 6−15

3 16−30

4 31−60

5 > 60

done in 5% steps, using a photo catalogue with exemplary images of damaged leaves for the purpose of comparison. Based on the mean injury degree of each of the three reference leaves, the mean leaf injury was calculated for each bioindicator station and exposure period. The leaves were also checked for plant diseases and mechanical damage, e.g., due to storms or vandalism. Such kind of leaf damage was occasionally observed, then leaves or whole plants were not further considered for ozone injury assessment. From the raw data of the injury assessments, the mean percentage of leaf injury was computed and classified into different ozone impact classes according to a five-step scale (Table 1). At the end of each experimental year, the mean percentages of leaf injury from all exposure series were also determined at each station. This calculation was the basis for the comparative statistical evaluation within the network that included analysis of variance (ANOVA) and pairwise comparisons of means using the Tukey test.

2.6. Quality assurance and control The entire project placed special emphasis on the standardisation of all procedural steps from plant cultivation and exposure at the monitoring sites to data acquisition and processing. This strict harmonisation was designed to eliminate potential external factors that could influence plant response and to reduce methodological error. The processes of quality assurance and quality control therefore covered all aspects of the bioindication procedure:











All material necessary for cultivation and exposure such as seed stocks, plant pots, substrate, fertiliser and exposure facilities was procured centrally and dispatched to the cities. A detailed and comprehensively illustrated handbook describing the procedures of cultivation, field exposure and injury assessment in different languages—and designed as a practical guide even for untrained technicians—was provided to all working groups. Practical demonstrations of the key operational steps were organised at the beginning and during the course of the project. Methodological compliance by the local teams was checked during repeated on-site visits by the coordination team.

3. Results and discussion 2.5. Comparative evaluation of ozone pollution and ozone-induced injury

3.1. Ozone-induced leaf injuries

Hourly or half-hourly ozone concentration measurements were obtained from monitoring stations routinely operating at or close to the biomonitoring sites (cp. Klumpp et al., 2006). Mean concentrations per day, biweekly exposure period and whole experimental season were computed, and cumulative exposure indices (AOT20, AOT40) were calculated as described by the EU Directive (EU, 2002). Details on ozone monitoring and calculation of ozone descriptors are given in Part I of this paper (Klumpp et al., 2006). Ozone exposure parameters (mean, AOT20, AOT40) and degree of ozoneinduced injury on tobacco leaves were comparatively evaluated by Spearman rank correlation and linear regression analysis. All statistical procedures were performed using the WinStat software package.

Typical ozone-induced injuries were recorded on the leaves of exposed tobacco plants in all cities of the network and during all three study years. However, while more than 70% of the visual assessments revealed ‘‘very weak’’ to ‘‘moderate’’ grades of leaf injury in Sheffield, Edinburgh and Copenhagen, these injury classes appeared much less frequently in Barcelona (14%) and Lyon (10%). Here, ‘‘strong’’ and ‘‘very strong’’ ozone effects dominated. The monitoring networks in Du¨sseldorf, Nancy, Klagenfurt and Verona occupied an intermediate position in this respect. Most assessments here lay in the range of ‘‘moderate’’ and ‘‘strong’’ ozone effects, whereby the extreme classes of 1 and 5 (‘‘very weak’’ and ‘‘very strong’’ effects) were rather rare. In the Stuttgart network, which cannot directly be compared with the other networks because of its

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broad agreement with the known distribution of tropospheric ozone concentrations over Europe (EEA, 2003; Sanz et al., 2004; Klumpp et al., 2006): a clear gradient with increasing ozone impact from northern to central and southern Europe was observed. An analysis of variance (ANOVA) and subsequent comparison of means using the Tukey test revealed significant differences in ozone effects between the cities. The monitoring networks in Lyon and Barcelona in particular differed from the other cities.

more suburban/rural nature, more than 50% of the assessments revealed ‘‘strong’’ or ‘‘very strong’’ ozone damage to the tobacco plants. The pollution pattern therefore resembled those in Nancy and Klagenfurt, i.e. a higher proportion of extreme values. In Valencia, data from only four exposure series during 2001 were available; they showed ‘‘very strong’’ ozone injury during one exposure series and only ‘‘moderate’’ to ‘‘weak’’ ozone injury during the other campaigns. For Glyfada, which joined the project in late 2001, only data from 2002 was available. ‘‘Very strong’’ leaf damage was recorded. The latter two cities were not further considered when comparing local networks. The average percentage of leaf injury (mean value from eight exposure series) was computed for each site. The distribution of these mean site values in the individual cities is depicted in Fig. 1. In this boxwhisker plot the central box shows the lower and upper quartiles and the median, and the whiskers extend to the maximum and minimum values. The lowest site mean in the entire monitoring network (7%) was recorded at the ‘Tinsley’ site in Sheffield, the highest site mean (83%) at ‘Feyzin’ in Lyon. Within the local monitoring networks, most of the site means lay within a relatively small range (cf. 25–75% boxes of the plot). The values are in

3.1.1. Spatial variability of ozone-induced injuries within the local monitoring networks in 2001 Unlike the comparison between the cities, no significant differences between individual stations within the local networks were generally observed in 2001. This is reflected in the relatively short whiskers in Fig. 1. The difference between the highest and lowest site mean was at most one grade in the five-step evaluation scale. This is confirmed by the mean leaf injury and the most extreme values for the local monitoring networks (Table 2). In most cities the lowest site means occurred at urban bioindicator stations due to ozone depletion by higher NO levels in city centres. Strongest effects typically occurred in suburban districts and in areas

100 90 g

25-75%

80

Median

% leaf injury

70

f

5

Min-Max

60 50

de

cde

e

4

bd

40 abc

ab 30

a

a 3

20 2

10

1

0 Ed

Sh

Co

Dü

Na

St

Kl

Ve

Ly

Ba

Fig. 1. Distribution of the site means within the local city monitoring networks in 2001 (25–75% box: range including 50% of the site means in the individual cities), classification of ozone-induced injury degree according to the five-stepped scale (solid horizontal lines and right y-axis) and results of the Tukey test. Ed ¼ Edinburgh; Sh ¼ Sheffield; Co ¼ Copenhagen; Du¨ ¼ Du¨sseldorf; Na ¼ Nancy; St ¼ Stuttgart; Kl ¼ Klagenfurt; Ve ¼ Verona; Ly ¼ Lyon; Ba ¼ Barcelona. Local networks with significant (po0.05) differences to others are marked by different lowercase letters.

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Table 2 Mean leaf injury as well as maximum and minimum biweekly site means within the local monitoring networks in 2001

Edinburgh Sheffield Copenhagen Du¨sseldorf Nancy Stuttgart Klagenfurt Verona Lyon Barcelona

Mean leaf injury of local network (%)

Maximum site mean (%)

Minimum site mean (%)

25 19 20 26 38 36 38 32 72 58

30 26 26 33 45 42 42 39 83 72

16 urban 7 urban 13 urban 16 urban 28 urban 26 suburban/reference 31 suburban 29 suburban/reference 64 urban 42 urban

suburban/reference suburban suburban suburban/reference reference suburban reference suburban industrial reference

Coloured labelling according to the five-step evaluation scale.

with comparably low pollution by primary pollutants (reference stations). Such distribution patterns of ozone effects in urban agglomerations are known from several other biomonitoring programmes (Mignanego et al., 1992; Godzik, 2000; Nali et al., 2001; Stabentheiner et al., 2004; Kostka-Rick and Hahn, 2005). The present study, however, did not verify statistically significant differences between urban and traffic-exposed sites on one hand and suburban and reference sites on the other hand when pooling data from all local networks. 3.1.2. Seasonal variations of ozone-induced leaf injuries within the local monitoring networks during the period 2000– 2002 Contrary to the relatively low spatial variation within the local networks, strong seasonal and interannual differences in ozone-induced leaf injury were caused by the variable meteorological conditions and related ozone concentrations. Figs. 2–4 exemplarily illustrate ozone effects at individual bioindicator stations in Du¨sseldorf, Klagenfurt and Lyon, encompassing the entire study period between July 2000 and July 2002. The relatively long whiskers at most sites reflect the high variability in plant injury due to varying ozone concentrations and weather conditions during the individual exposure periods. In Du¨sseldorf, the most severe leaf damage during a total of 15 biweekly exposure series was registered in July 2001 (78%, ‘Mo¨rsenbroicher Ei’ site), whereas in some periods no injury at all was detected at the same site. In Klagenfurt, the most severe leaf damage occurred in August 2000, with values of approximately 80% at the sites ‘Sattnitz’, ‘Wo¨rthersee’ and ‘KoschatstraXe’. Compared with Du¨ssel-

dorf the mean values were higher at all stations. Maximum values (480%) were also recorded in individual exposure series at all stations in Lyon, particularly during 2001, but variability at all sites was also very strong between different exposure series. 3.2. Relationships between ozone pollution and ozone-induced injury The relationship between ozone pollution and ozone-induced injury was studied by pooling data from 16 exposure sites in all cities except for those networks (Barcelona, Valencia) where less than five data pairs (tobacco exposure/ozone concentration) were available in 2001. A highly significant correlation was found between foliar injury degree and various descriptors of ozone pollution such as mean value, AOT20 and AOT40, although the relationships were not very strong. Table 3 lists the computed correlation coefficients for comparisons based on single biweekly exposure periods (n ¼ 112) and on the entire exposure time from late May to mid-September (n ¼ 16). The correlation coefficients were similar for all three tested ozone parameters. For the data pairs based on biweekly exposure periods, all coefficients were significantly different from 0 (r ¼ 0: no correlation), although they only reached a comparably low value of 0.32. When ozone and tobacco data within the local monitoring networks were aggregated over the entire study period (late May to mid-September), the correlation coefficients clearly increased (r ¼ 0.56–0.61). When differentiating between urban and suburban sites, correlation coefficients of

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100 25-75% 90 Median Min-Max

80

70

% leaf injury

60

50

40

30

20

10

0 Airport suburban

Hubbelr. reference

Lörick suburban

Mörsenbr. Ei street

Heyestr. suburban

Graf-Adolf street

Suitbertus urban

Further suburban

Stettiner suburban

Fig. 2. Ozone effects on tobacco Bel-W3 in the Du¨sseldorf monitoring network (2000–2002).

urban sites rose to r ¼ 0.43–0.49 for single exposure periods and to 0.76–0.79 for the whole experi mental season. Suburban sites, by contrast, showed weaker correlation for the individual exposure periods and no significant relationship for the entire period. Ribas and Pen˜uelas (2003), in a biomonitoring study in rural Catalonia (Spain), found strong correlations (r40.97) between AOT20 and AOT40 values and ozone effects on leaves of tobacco BelW3 when leaf damage was categorised in 10% intervals. Hence, we reran our statistical analyses considering the damage classes proposed by those authors or the five damage classes used by the present study instead of the exact percentage of injured leaf area. The correlation analyses based on categorised leaf injury, however, did not produce significantly different results. Only at suburban sites were slightly stronger relationships between AOT values and categorised leaf injury observed

(data not shown). This may be due to the higher variability in site characteristics (ozone concentrations, meteorological conditions) in our study versus in the relatively limited area in Catalonia. Examining individual sites of the local networks separately, however, yielded noticeable differences in the correlation between ozone pollution and ozone-induced effects. In Lyon, for example, no association was found between different ozone descriptors and corresponding tobacco data. Already at comparably low AOT20 values of 1100 ppb h, very strong ozone injury appeared on exposed tobacco plants. In Du¨sseldorf, by contrast, descriptors of ozone pollution (AOT20 and mean concentration) and the corresponding leaf injury at ‘Lo¨rick’ site were almost linearly associated (Fig. 5). Similar linear relationships between ozone pollution (as AOT20) and tobacco injury were also found in 2000 in Barcelona when only urban sites and only

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25%-75%

90

Median Min-Max

80

70

% leaf injury

60

50

40

30

20

10

0 Sattnitz industrial

Wörthersee suburban

Koschat street

Mageregg rural

Wölfnitz rural

Annabichl suburban

Hörtendf. Suburban

Völkermarkt street

Fig. 3. Ozone effects on tobacco Bel-W3 in the Klagenfurt monitoring network (2000–2002).

exposure periods with stable weather conditions were considered (Ribas and Pen˜uelas, 2002). Efforts to determine relationships between ambient ozone concentrations or doses and symptomatology of tobacco and other bioindicator plants have repeatedly been undertaken, but with variable success. In smallscale studies and under relatively homogeneous meteorological conditions, even linear relationships between both pollution and effect criteria may be found (Heggestad, 1991; Biondi et al., 1992; Mignanego et al., 1992; Nali et al., 2001; Kostka-Rick, 2002; Ribas and Pen˜uelas, 2002; Cuny et al., 2004). Variable relationships between ozone injury and ozone concentrations at different sites and in different studies may partly be attributed to the fact that air pollution monitoring stations and bioindicators cannot not always be installed side by side (cp. Table 1 in Part I). Thus, actual ozone values affecting the tobacco plants may differ from the measured concentrations. Additionally, it should be stated that it normally takes some time (1, 2 days) for the ozone injury to develop, and therefore the periods used for calculating ozone

concentrations and those responsible for ozone injury development are not exactly the same. In large-area networks like those presented here, however, it is of major importance that the ozone concentration may account for only a small part of the variance in symptomatology: this is especially true under strong spatial and temporal meteorological variations. It is widely accepted that the ozone flux through the stomata into the leaf and the consequential cumulative ozone uptake rather than ambient ozone concentrations determine ozoneinduced effects on plants. This flux, however, is modified by various environmental factors such as temperature, humidity and wind speed (Pen˜uelas et al., 1999; Pihl Karlsson et al., 2004; Filella et al., 2005). Flux models would therefore be needed to quantitatively link ozone to plant response. This approach was outside the scope of the present project. The advantage of exposing sensitive bioindicators like tobacco Bel-W3 is that the impact of the effective ozone dose on the plant can directly be measured comparatively simply. Some authors

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100

90

80

70

% leaf injury

60

50

40

30 25-75%

20

Median 10

Min-Max

0 Solaize industrial

Feyzin industrial

Airport reference

Etats Unis street

Berthelot street

St. Just urban

Cr. Luizet urban

Fig. 4. Ozone effects on tobacco Bel-W3 in the Lyon monitoring network (2000–2002).

Table 3 Spearman rank correlation coefficients rs between different ozone parameters and ozone effects (assessed as % leaf injury) considering biweekly exposure periods and entire exposure duration of up to eight biweekly periods Type of site

Ozone parameters

Biweekly exposure periods

Entire exposure duration

Mean concentration AOT40 AOT20

n ¼ 112 0.32*** 0.32*** 0.32***

n ¼ 16 0.56* 0.59** 0.61**

Mean concentration AOT40 AOT20

n ¼ 54 0.43*** 0.48*** 0.49***

n¼8 0.76* 0.79* 0.76*

Mean concentration AOT40 AOT20

n ¼ 58 0.28* 0.27* 0.29*

n¼8 0.33ns 0.29ns 0.26ns

All

Urban

Suburban

*Significant at po0,05.**Significant at po0.01.***Significant at po0.001.ns Not significant.

argue that the degree of ozone-induced injury on tobacco leaves provides a better basis for the risk assessment of incidence or extent of ozone-induced

leaf injury in crops than do any descriptors of ambient ozone concentrations or doses (KostkaRick, 2002).

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R2 = 0.76

70 % leaf injury

60 50 40 30 20 10 0 0

1000

2000

3000

4000

5000

AOT20 [ppb*h] 100 90 80

% leaf injury

70

R2 = 0.88

60 50 40 30 20 10 0 0

5

10

15

20

25

30

35

Mean ozone concentration [ppb]

Fig. 5. Scatter plot (with regression line and coefficient of determination R2) of the relationship between ozone-induced leaf injury and AOT20 (above) or mean ozone concentration (below) at the ‘Lo¨rick’ site in Du¨sseldorf during 2001.

4. Final remarks The highly standardised biomonitoring procedure with tobacco Bel-W3 based on a draft version of the VDI-Guideline (2003) was successfully applied over a large geographical area ranging from Scotland to Greece. It proved its value in demonstrating and quantifying ozone-induced effects on plants. In strongly ozone-polluted regions with potentially

extreme foliar damage it might be recommendable to expose less sensitive cultivars like Bel-B in parallel and to use younger leaves as reference leaves for injury assessment. Such modifications have been incorporated in the finally published guideline (VDI, 2003), which now serves as a starting point for the Europe-wide standardisation of this methodology (Nobel et al., 2005). In this context, a further outcome of the EuroBionet

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project is the recommendation to cultivate the bioindicator plants in filtered air as far as possible: how exposure to elevated ozone levels during greenhouse cultivation might influence plant sensitivity during subsequent outdoor exposure remains to be clarified (Heagle and Heck, 1974; Schraudner et al., 1998). Such an additional standardisation step may help reduce the variability of plant response to ambient ozone. Our studies demonstrated that ozone pollution and ozone-induced effects generally increased along a gradient from northern Europe to central and southern Europe in the study year 2001, but that topographic characteristics and the distribution of air pollutant emissions may strongly influence ozone pollution and its impact on the local scale (Ribas and Pen˜uelas, 2003; Klumpp et al., 2006). Although highest ozone burdens and strongest ozone-induced plant injuries occurred in rural and suburban sites, we show that ozone pollution may reach high levels also at central locations and even at street sites. The widespread occurrence and geographical pattern of ozone-induced plant injury in Europe, as determined here through tobacco exposure mostly at urban and suburban sites, widely corresponded to the findings of the UNECE network, which uses differentially sensitive white clover clones to assess ozone-induced injury mostly in rural areas (Harmens et al., 2004). Ozone-induced injury on sensitive indicator plants cannot directly be translated into impact on native vegetation or crops. Nonetheless, the relationships between the sensitivity of bioindicators and other plant species underline the value of the former as an indicator of potential vegetation damage under given pollution and climate conditions (Kostka-Rick and Hahn, 2005). Finally, our studies demonstrated that tobacco plants are outstanding tools for environmental communication and education: they make the noxious effects of ozone pollution visible to citizens in their everyday life (Klumpp et al., 2004). Acknowledgements This study was supported by the LIFE Environment Programme of the European Commission, DG Environment, under the Grant LIFE/99/ENV/ D/000453. We thank the following local and regional authorities and their respective project leaders and co-workers for their valuable support: Landeshauptstadt Du¨sseldorf, Umweltamt (H.-W. Hentze, M. Wiese), Communaute´ urbaine

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de Lyon, Ecologie urbaine (O. Laurent), Comune di Verona, Servizio Ecologia (T. Basso, N. Belluzzo, S. Oliboni, S. Pisani, R. Tardiani), The City of Edinburgh Council, Air Quality Section (T. Stirling), Sheffield City Council, Environment & Regulatory Services (G. McGrogan, N. Chaplin), Landeshauptstadt Klagenfurt, Abt. Umweltschutz (H.-J. Gutsche), City of Copenhagen, EPA (J. Dahl Madsen), Generalitat de Catalunya, Dept. Medi Ambient, Barcelona (X. Guinart), Communaute´ Urbaine du Grand Nancy (F. Perrollaz), City of Glyfada (G. Kolovou), and Ayuntamiento de Valencia, Oficina Te`cnica de la Devesa-Albufera (A. Vizcaino, A. Quintana) as well as the municipalities of Ditzingen, Plochingen, Deizisau and Altbach (Germany). Gratitude is also expressed to the staff of all institutions involved in the present studies, and to M. Stachowitsch for proof reading the English manuscript.

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