Adult ash trees (Fraxinus excelsior L.), known to be sensitive or tolerant to ozone, determined by presence or absence of foliar symptoms in previous years, were treated with ethylenediurea (EDU) at 450 ppm by gravitational trunk infusion over the 2005 growing season (32.5 ppm h AOT40). Tree and shoot growth were recorded in May and September. Leaf area, mycorrhizal infection, and leaf and fine root biomass were determined in September. EDU enhanced shoot length and diameter, and the number and area of leaves, in both O 3 -sensitive and tolerant trees. However, no EDU effects were recorded at the fine root and tree level. Therefore, a potential for EDU protection against O 3 -caused growth losses of forest trees should be evaluated during longer-term experiments. KEYWORDS: European ash, ethylenediurea, forest, growth, mycorrhizae, tropospheric ozone INTRODUCTION Much has been written about the effects of O 3 on growth of forest trees, but conclusive proof that ambient levels of O 3 affect growth of forest trees remains elusive, usually because the experimental techniques do not allow extrapolation to realistic conditions Paoletti et al.: EDU Effects on Tree Growth TheScientificWorldJOURNAL (2007) 7(S1), 128-133 129 MATERIALS AND METHODS Six O 3 -sensitive (symptomatic) and six O 3 -tolerant (asymptomatic) adult ash trees, determined by presence or absence of foliar symptoms in previous years, were gravitationally infused with 450 ppm ethylenediurea (EDU) or water at 3-week intervals from May to September, 2005. AOT40 over the period was 32.5 ppm h. The experimental site was located at the 34-ha "Millerose" park in Turin, Italy. Details about infusion methodology, site characteristics, and EDU protection from O 3 visible injury are presented elsewhere Measurements of tree and shoot growth were carried out in May and September, while biomass, leaf area, and fine root mycorrhizal infection were determined only in September. Tree diameter was measured at breast height by means of a calliper. The points of measurements were labelled to reduce the error from May to September. Tree height was measured with a clinometer (Model CM360PA, Silva, Sweden). Shoot growth was measured on one 1-year-old sun shoot per tree, from the lower crown part. The shoots were the terminal ones of a lateral branch and were randomly selected. The total number of leaves and leaflets per shoot was counted. Shoot length and base diameter were recorded by means of a ruler and a digital calliper, respectively, with 0.1-mm accuracy. In September, 3 shoots per plant were collected. Total leaflet area per shoot was determined with an AM300 area meter (ADC, BioScientific Ltd, Herts UK). Shoot biomass was determined by oven-drying at 65 °C until a constant weight was reached. Leaflet mass per unit of leaflet area (LMA) and leaflet water content (LWC = (fresh weight-dry weight)/dry weight) were calculated Fine roots (diameter<2 mm) were sampled in standard cores of soil (500 ml). Four cores per tree were collected 40 cm far from the trunk along the cardinal points and joined in a single sample. Roots were attributed to F. excelsior with the help of morphological and anatomical observations The statistical unit was the single tree. After checking for normality, data were analyzed using a twoway (EDU x tree O3-sensitivity) analysis of variance (Statistica 6.0, StatSoft, Tulsa, OK). RESULTS EDU significantly reduced the abscission of leaves and induced a larger increment of the shoot length and diameter over the growing season, compared to the water-infused trees Paoletti et al.: EDU Effects on Tree Growth TheScientificWorldJOURNAL EDU Symptomatic 8.0 ± 1.8 2.5 ± 2.5 -6.2 ± 2.3 -7.9 ± 1.7 17.5 ± 8.8 11.1 ± 2.7 EDU Asymptomatic 2.0 ± 0.8 1.1 ± 1.0 1.8 ± 0.9 2.8 ± 2.5 17.5 ± 5.5 15.3 ± 0.2 WATER Symptomatic 5.1 ± 2.7 0 -7.7 ± 1.0 -10.6 ± 1.9 6.7 ± 1.2 6.0 ± 2.0 WATER Asymptomatic 1.0 ± 0.9 2.4 ± 4.0 -2.8 ± 3.5 -6.9 ± 2.4 7.7 ± 4.4 4.6 ± 2. Paoletti et al.: EDU Effects on Tree Growth TheScientificWorldJOURNAL DISCUSSION EDU enhanced shoot length and diameter, and reduced leaf abscission. The stimulating effect of EDU on shoot growth did not translate into a stimulation of growth at the fine root and whole tree level, during one growing season. Overall, EDU effects were slight, and not enough to significantly affect the total leaf biomass. Increased growth in the EDU-treated plants over the non-EDU-treated ones has been reported in several species (Phaseolus vulgaris[18] Symptomatic trees did not show a marked reduction in growth compared to the asymptomatic trees. At the shoot level, we recorded a stimulation of leaf abscission. Part of the photosynthate may have been used to prevent or repair foliar damage rather than going toward growth In conclusion, gravitational infusion of EDU resulted in stimulation of shoot growth in both O 3 -sensitive and tolerant ash trees exposed to elevated ambient O 3 concentrations (32.5 ppm h AOT40). Ainsworth et al
