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BEDNÁŘOVÁ, E., KUČERA, J.: Monitoring the damage to epicuticular waxes at silver birch (Betula pendula Roth.) in the changing air pollution spectrum of the Ore Mountains. Acta univ. agric. et silvic. Mendel. Brun., 2011, LIX, No. 5, pp. 9–16 The paper deals with the study of damage to the assimilatory apparatus of silver birch (Betula pendula Roth) using the study of changes of epicuticular waxes in the period 1997 to 2009. During the period, changes in the air pollution spectrum occurred in the area of the Ore Mountains. At the beginning of the monitoring, above-limit concentrations of sulphur oxides were the main anthropogenic factor. These concentrations resulted in the degradation of epicuticular waxes. Statistical evaluations demonstrated the high dependence of damage to epicuticular waxes on high concentrations of sulphur oxides. Damage to epicuticular waxes by air pollution increased with the increasing altitude of a forest stand. Since 2001, measured values of SO2 decreased to a minimum but a new phenomenon appeared damaging the assimilatory apparatus of forest stands, namely above-limit concentrations of ground ozone. These above-limit concentrations of ground ozone damage the assimilatory apparatus including epicuticular waxes at all silver birch stands occurring at altitudes above 800 m. This fi nding was also proved by the high coeffi cient of determination. birch (Betula pendula Roth.), air pollution, epicuticular waxes, altitude, damage, sulphur oxides, ground ozone In the 80s of the 20th century, considerable damage to forest stands occurred by high concentrations of sulphur dioxide in the Ore Mountains. A er 1989, a marked decrease of air-pollution load occurred but at the highest locations of the Ore Mountains, concentrations of sulphur oxides reached always above-limit values for forest trees, which became evident on the health condition of silver birch. In case of damage to the assimilatory apparatus by air pollution, functional disturbances and fi nally also abnormalities in the morphology of leaves occur fi rst. These disturbances refl ect largely physiological processes (Hoad et al., 1998). The plant epidermis with cuticle and waxes are damaged as the fi rst due to the infl uence of external factors on the plant (Tuomisto and Neuvonen, 1993). Due to the eff ect of air pollution, the loss of waxes occurs together with the change of structures of epicuticular waxes (Hoad et al., 1992). The cuticle with wax surface increases the resistance of leaves against the penetration of gases such as SO2, O3 and NOx. Properties of cuticle also largely aff ect the accumulation and subsequent behaviour of pesticides, growth regulators, leaf nutrients and other chemical preparations (Ylimartino et al., 1994). In recent ten years, the change in the air pollution spectrum occurred at high-altitude areas of the Czech Republic. Sulphur oxides decreased to minimum values but abovelimit concentrations were measured of ground ozone for forest ecosystems. At present, ozone is considered to be the most important gaseous harmful substance aff ecting the health condition of forests in Europe (Ashmore, 2003). The harmfulness of ozone depends on the detoxication capacity of 10 E. Bednářová, J. Kučera a plant diff ering at particular tree species (Ditmar et al., 2004). In various experiments, relatively high susceptibility of birch was demonstrated (Skelly et. al., 1998, Päakkönen et al., 1998, Karnosky et al., 2002, 2003). At the necrosis of cells of upper mesophyll, damage caused by chlorosis and necrotic spots on leaves becomes visibly evident. In addition to leaf damage, ozone also aff ects unfavourably the total energy balance of trees, which results in the reduction of resistance to other stress factors (Jones et al., 2004). MATERIAL AND METHODS In the period 1997 to 2009, damage to the assimilatory apparatus of silver birch (Betula pendula Roth.) was evaluated by the method of changes in epicuticular waxes in the altitudinal gradient from 600 to 1000 m of the Ore Mountains, namely on ten research plots of the second age class in relation to the changing air pollution spectrum and environment parameters. Sampling the plant material was carried out on the fi rst week in September, always from three trees of each of the monitored localities. The amount of epicuticular waxes on the leaf surface was determined in the laboratory according to the method of Günthardt et al. (1994). Measured values of SO2 concentrations in 1997 to 2001 were obtained from stations of the ČHMU (Czech Hydrometeorological Institute) occurring in the vicinity of the monitored silver birch stands. From 2003, concentrations of ground ozone were measured directly in the evaluated stands using passive dosimeters of Gradko Co. UK. Every-year installation of passive dosimeters occurred in the phenological stage “foliage beginning” 100%. The passive dosimeters were tested compared to AIM ozonometers (Czech Hydrometeorological Institute) with very good results (Šrámek et al., 2007). At all research plots, air temperatures were continually measured in the lower part of crowns where also the passive dosimeters were placed in four weeks intervals. Solar radiation and precipitation were monitored in the open area. RESULTS AND DISCUSSION At the beginning of our monitoring in 1997–1999, above-limit concentrations of sulphur oxides for forest trees were measured in the Ore Mountains also in the summer season (SO2 concentrations exceeding 20 μg. m3 (Fig. 1). Mean monthly maxima of SO2 reached 49 μg.m −3 at these localities in summer months, which proved negatively in the quantity and quality of epicuticular waxes of silver birch (Bednářová, 2001). The development of epicuticular waxes at silver birch in the Ore Mountains in the period 1997 to 2009 is characterized by Figs. 2 and 3. Literature sources (Turunen et al., 1995) mention that even short-term exceeding above-limit concentrations of sulphur oxides shows irreversible negative impacts on the degradation of epicuticular waxes in forest trees. In 1998, lower concentrations of sulphur oxides were measured at all localities as against 1997. At lower altitudes, the decline of sulphur oxide concentrations by 32% occurred and at higher altitudes, the air pollution load decreased even by 55% as compared to values from the previous year. This change showed itself favourable in the condition of epicuticular waxes. In 1997, 53 mg. g−1 DM (dry mass) were detected on leaves from the lowest (alt. 600 m) research plot and in silver birch stands at the highest altitude (1 000 m) only 34 mg.g−1. Quantitative analyses of the plant material in 1998 demonstrated the higher amount of epicuticular waxes on silver birch leaves at all altitudes of monitored stands as compared to the previous 1: Mean monthly concentrations of SO2 μg. m −3 in monitored areas of the Ore Mountains in the period May to August Monitoring the damage to epicuticular waxes at silver birch (Betula pendula Roth.) 11 year. At an altitude 600 m, 55 mg.g−1 DM (dry matter content) leaves were measured and in stands at an altitude of 1 000 m some 35 mg. g−1 DM leaves were found. This situation is characterized in Figs. 1 and 3. In 1999, another decline the SO2 air pollution load occurred, which resulted in the repeated increasing the amount of epicuticular waxes on birch leaves in the period of leaf sampling (at the beginning of September). In monitored stands at higher altitudes, the increased amount of epicuticular waxes on birch leaves occurred in 1999, namely as many as by 27% as against 1998. An increase in the total amount of epicuticular waxes on birch leaves became mostly evident at stands growing at higher altitudes together with the marked decline in the concentration of sulphur oxides in this year. Since 1999, the amount of epicuticular waxes from stands at lower altitudes (600–800 m) ranges nearly at the same level. Only at the Litvínov stand at an alt. of 800 m, the higher loss of epicuticular waxes occurred in 2006, which could be possible to explain by high concentrations of ground ozone at altitudes exceeding 800 m in this year. Within the period of monitoring, the decreasing amount of epicuticular waxes was demonstrated on leaves with the increasing altitude of monitored stands, which is proved by a determined dependence R2 = 0.8969 (y = −0.0473x + 86.24). Above-limit concentrations of sulphur oxides resulted in the degradation of epicuticular waxes and decreasing 2: Amount of epicuticular waxes in birch (Betula pendula) in lower altitudes 3: Amount of epicuticular waxes in birch (Betula pendula) in higher altitudes 12 E. Bednářová, J. Kučera their total amount on the leaf surface, which was expressed by high dependences evident from Fig. 4. Fig. 5 characterizes the level of the measured amount of epicuticular waxes at silver birch growing in the immediate vicinity of stations measuring the sulphur oxide concentrations in the period 1997 to 2001. In 2000, measured values of sulphur oxides decreased to insignifi cant values throughout the altitudinal gradient, however, since 2000, gradual increasing the ground ozone concentrations occurred in forest stands. In 2001, the average concentration of ground ozone was measured (in the Ore Mountains at an alt. 800 m at CHMI stations) for the period May to August, namely 91.00 μg. m−3, which exceeds a limit for forest trees amounting to 80 μg.m−3. In 2002, the average value of ozone concentrations 92 μg.m−3 was determined for the same period. Since 2003, above-limit concentrations of ground ozone were measured at six long-term monitored plots occurring at altitudes 600 to 1 000 m (Fig 8). At all higher-situated plots, lower amounts of epicuticular waxes were measured on birch leaves as against the previous year. Increased concentrations of ground ozone resulted in the higher degradation of epicuticular waxes, which became evident in the destruction of waxes (Fig. 6) and their total loss. Fig. 6 chara