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/lp/de-gruyter/ozone-phytotoxicity-in-the-western-carpathian-mountains-in-slovakia-LjcdgLopUF
- Publisher
- de Gruyter
- Copyright
- Copyright © 2016 by the
- ISSN
- 0323-1046
- eISSN
- 0323-1046
- DOI
- 10.1515/forj-2016-0008
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- See Article on Publisher Site
Abstract
In this work, the response of temperate coniferous forests to ozone air pollution (O3) in the mountain environment of the High Tatra Mts. (Western Carpathians) was analyzed. The modelling of stomatal O3 flux is a complex method for the estimation of phytotoxicity of O3 pollution to forest vegetation. Stomatal flux-based critical levels (CLef) for effects of O3 on radial growth take into account the varying influences of O3 concentration, meteorological variables, soil properties, and phenology. The application of the model DO3SE (Deposition of Ozone for Stomatal Exchange) at five experimental plots with altitudes varying from 810 to 1,778 m a.s.l. along vertical and spatial profile in the High Tatra Mts. revealed the high phytotoxic potential of O3 on spruce forests during the growing season 2014. The accumulated stomatal O3 flux above a threshold of Y (1 nmol m2 s1), i.e. POD1 (Phytotoxic Ozone Dose) ranged from 13.6 mmol m2 at the Kolové pleso site (1,570 m a.s.l.) to 16.2 mmol m2 at Skalnaté Pleso site (1,778 m a.s.l.). CLef for POD1 (8 mmol m2) recommended for the protection of spruce forests were exceeded at all experimental plots from early July. Similarly, AOT40 index suggests vulnerability of mountain forests to O3 pollution. AOT40 values increased with altitude and reached values varying from 6.2 ppm h in Stará Lesná (810 m a.s.l.) to 10.7 ppm h at Skalnaté Pleso close to the timber line (1,778 m a.s.l.). Concentration-based critical level (CLec) of 5,000 ppb h was exceeded from June to August and was different for each experimental site. Key words: mountain forests; Phytotoxic Ozone DoseY; DO3SE model; stomatal conductance; stomatal ozone flux Editor: Bohdan Konôpka 1. Introduction Ozone levels in Europe are rather high to jeopardize human health and vital growth of vegetation (WHO 2008; Paoletti 2014; Monks et al. 2015). Relevant reduction of O3-precursors emissions in Europe (Vestreng et al. 2004) tends to decrease O3 maxima and increase annual averages at both urban and rural sites (Paoletti et al. 2014) due to less O3 titration by reduced NOx emissions. The ozone levels are increasing in cities and decreasing at Mediterranean remote sites (Sicard et al. 2013). However, cumulative indices such as SOMO35 and AOT40, i.e. 5,000 ppb h (Directive 2008/50/EC) indicate that rural highland sites of Europe are more vulnerable to health and environmental risks associated with perpetual O3 exposure than urban lowland areas (Bicárová et al. 2013). Concentration-based critical level (CLec) of AOT40 for forest ecosystems is regularly exceeded in almost whole territory of Slovakia (Pavlendová 2008) as well as in the Czech Republic (Hnová & Schreiberová 2012; Hnová et al. 2016). At high-altitude stations, the background O3 levels (chronic exposure) are higher, and higher O3 concentrations are observed at night (Sicard et al. 2009). Acute exposures are characterized by high O3 concentrations for a relatively short time period, within hours or days that lead to visible foliar injury (Schaub et al. 2010; Sicard et al. 2011). Chronic exposures involve lower concentrations that persist or recur over a period of weeks or months (Grulke et al. 2007). Mountains can act as cold-traps for long-range transport of atmospheric pollutants. The mechanism of transport of pollutants through the atmosphere and accumulation in the mountain environment were well described in literature (Steinbacher et al. 2004; Sicard et al. 2009, 2011; Monks et al. 2015). For example, there is evidence of accumulation of persistant organic pollutants (POPs) in the mountainous environment (Hageman et al. 2015). The highest deposition fluxes of organochlorine compounds (OCs) were found at high-altitude European sites, especially at Skalnaté Pleso in the High Tatra Mts. (Arellano et al. 2015). Tropospheric ozone acts as a phytotoxin which produces an oxidative stress in plants. The phytotoxic nature of O3 can impair forest productivity by both favouring stomatal closure and impairing stomatal control. High O3 concentrations reduce carbon assimilation in trees while this reduction is more related to stomatal O3 deposition than to O3 concentration (Fares et al. 2013). The scientific community is moving toward an evaluation of the ozone risk based on stomatal O3 fluxes (Matyssek et al. 2007; UN-ECE 2010; Mills et al. 2011; Büker et al. 2012). Tracking of stomatal O3 uptake by vegetation required more comprehensive methods than the evaluation of O 3 concentration data alone. Multiplicative models of stomatal conductance, such as the DO3SE (Deposition of Ozone and Stomatal Exchange), have been suggested as a basis for calculating the hourly O3 flux resulted to the Phytotoxic Ozone Dose (PODY) (Emberson et al. 2000). For forest trees, stomatal flux-based critical levels (CLef) of PODY were derived for effects on changes in annual increments in the whole tree biomass. These critical levels can be used to refer adverse health effects of O 3 on *Corresponding author. Zuzana Sitková, e-mail: sitkova@nlcsk.org, phone: +421 5314 158 S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 relevant ecosystem services provided by forest trees, e.g. production of roundwood, C sequestration, soil stability and flood prevention (Mills et al. 2011). Main problem is that present exposure-based standards for protecting vegetation from ozone (O3) do not reflect the actual field conditions. Recent knowledge resulting from epidemiological assessment of forest responses to O3 showed that a risk assessment based on PODY and on real plant symptoms is more appropriate than the concentration-based method and developed the new flux-based critical levels CLef for forest protection against visible O3 injury (Sicard et al. 2016). Previous studies concerning the problems of air quality pointed to the high level of ozone air pollution in the Western Carpathian Mts. that is comparable with the most polluted regions in Europe (Bytnerowitz et al. 2004; Bicárová et al. 2013; Hnová et al. 2016). Formation of O3 in mountain regions of Slovakia is substantially influenced by long-range transport of O3 precursors and their interaction with local components from both antropogenic and biogenic sources (Bicárová et al. 2005). It can be expected that high chronic O3 exposure and O3 uptake by vegetation may impair the vitality of forests, especially in wet and cold climate conditions of highland areas. The aim of this work is to quantify phytotoxical ozone dose for coniferous forest species, especially Norway spruce (Picea abies L. Karst) in the mountain environment of the High Tatra Mts. (Slovakia). Stomatal O3 fluxes and POD1 are calculated by DO3SE model for five experimental sites situated along spatial and vertical profiles from 810 to 1,778 m a.s.l. during the vegetation season 2014. The results are intendend to support new complex approach in research of adverse impact of O3 pollution on forest vegetation based on modelling of stomatal O3 flux. This new approach may improve still prevalently used O3 concentration based method associated with AOT40 indicator for the protection of vegetation and forests. Presented research can provide many results useful for the wide scientific community (in environmental and forest science, physiological and biological research, ecological modelling etc.). Research activities and field measurements are part of the ongoing project MapPOD (Mapping of Phytotoxic Ozone Dose in the Forest Environment of the High Tatra Mts.) which focuses on assessment of potential O3 risk to mountain forests in Slovakia. 2. Material and methods 2.1. Study area The High Tatra Mts. are located in the northern part of Slovakia on the border with Poland (Fig. 1). Region of interest represents the highest part in the whole Carpathian Mountains. The elevation of the main mountain chain of the High Tatra Mts. varies from about 2,000 m a.s.l. (saddles) to 2,654 m a.s.l. (the highest peak). Temperate coniferous forest with Norway spruce (Picea abies L. Karst.) is the dominant vegetation type up to 1,500 m a.s.l. From the other tree species occur European larch (Larix decidua Mill.), Scots pine (Pinus sylvestris L.) and Grey alder (Alnus incana L. Moench). The higher part of the valley (subalpine) is almost completely covered by Dwarf pine (Pinus mugo Turra). In order to model O3 fluxes, the O3 concentrations, meteorological and environmental parameters were measured at 3 experimental sites situated in the south aspect: Stará Lesná SL, Start STA, Skalnaté Pleso SP (Table 1, Fig. 1). On the north side of the High Tatra Mts., in the vicinity of Tatranská Javorina municipality, the other 2 experimental sites (Podmurá PDM and Kolové pleso KP) are located. On the south side, the massive rocky branches separate numerous glacial valleys including Skalnatá dolina area. Due to strong rain-shadow effect the climate of south-facing Skalnatá dolina area is slightly warmer and significantly drier Fig. 1. The geographical position of the High Tatra Mts. in the Carpathian Montane Forests and location of the experimental sites (SL Stará Lesná, STA Start, SP Skalnaté Pleso, KP Kolové pleso, PDM Podmurá). 78 S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 GranodioriteGranite Skeli-Dystric Leptosols Sandy loam coarse Skeli-Dystric Leptosols Silt loam medium coarse compared to north part of the High Tatra Mts. (Table 1). On the contrary, the climate of the north-facing Tatranská Javorina area is cold and very wet with long-term mean annual temperatures around 3.8 °C and rainfall total of 1,250 mm at the altitude of 1,100 m a.s.l. The meteorological observation during the last two decades revealed moderate warming and increasing rainfall amounts (SHMI 2015). In recent decades, the area of interest was affected by large-scale disturbances in connection with the adverse effects of climate change. The extreme weather conditions more frequently observed in the recent years (drought, heat waves, snow cover decline etc.) contributed to the massive bark beetle outbreaks (Ips typographus) in forest stands weakened by abiotic destructive factors as windstorm, fire, flooding, long-range transport of air pollutants etc. (Mezei et al. 2014; Nikolov et al. 2014). P196190 mm 1,220 1,250 AT196190 °C Silt loam medium coarse Soil texture Sandy loam coarse Gleyic Cambisols Cambic Podzols Cambic Podzols Soil type Loam medium 1,493 2.2. Meteorological and ozone data The basic meteorological variables (such as air temperature, relative humidity, wind speed, wind direction, solar radiation and precipitation) were continuously monitored at all experimental sites using automatic weather stations (EMS Brno CZ; Physicus, s. r. o. SK). The measuring interval of meteorological data was set on variable time step (starting from 10 seconds up to 510 minutes) and average data were consequently stored every 10 to 30 minutes into the central datalogger of the weather station. Ozone concentration data were measured at five experimental sites using the ozone analyzers based on the well established technique of absorption of UV light at 254 nm. At three experimental forest sites (Stará Lesná SL, Skalnaté Pleso SP, Podmurá PDM), the analyzers manufactured by Horiba (APOA360 Ambient Ozone Monitor) and Thermo Electron Environmental (49C Ozone Analyzer) were used. The more remote experimental sites where the electricity was unavailable (Start STA, Kolové pleso KP) were equipped by Ozone Analyzer Monitor M106-L (2B Technologies, Inc.) and powered by solar energy. The ozone data in default ppb units were measured in 610 second interval and hourly averages were stored into the datalogger. For purposes of this study, the hourly meteorological and O3 concentration data from the period of April to October of the year 2014 were processed and analysed. Geological subbase Granodiorite Granodiorite Fluvioglacial spruce, fir, rowan, beech, maple Norway spruce, Birch, Scots pine, European larch, Grey alder Mountain pine (8th) Mugethum acidifilum Mountain and swiss pine, spruce 1,570 Tree species composition spruce, larch, pine, fir, maple Mountain pine (8th) Mugethum acidifilum Mountain pine Granodiorite Used data sources: 1 forestry databases of National Forest Centre in Zvolen (soil, geological and typological maps, Forestry GIS-databases). 2 climate data provided by Slovak Hydrometeorological Institute for the reference period 19611990 and Climate Atlas of Slovakia (SHMI 2015). 3 soil units according to WRB Soil Classification System (WRB 2015, FAO). 4 forest typology and edaphic-trophic units based on Zlatnik's geobiocenological school (Zlatník 1976). Abbreviations: AT air temperature; P precipitation. Group of forest type Fluvioglacial Sorbeto Piceetum Lariceto piceetum Table 1. Experimental sites description (CODES used in relation to Fig. 1). SpruceFirBeech (6th) Vegetation zone Firbeech (5th) Altitude m asl 1,778 1,150 1,100 Spruce (7th) Sorbeto Piceetum Acereto Piceetum Pineto-Piceetum 2.3. DO3SE model The multiplicative deposition DO3SE model has been developed to estimate the risk of O3 damage to the European vegetation and it is capable of providing flux-modelling estimates according to UN-ECE LRTAP methodologies for effectsbased risk assessment (Pihl-Karlsson et al. 2004; Emberson et al. 2007; Karlsson et al. 2007; Tuovinen et al. 2007). Meteorological data, O3 concentration and plant-specific characteristics (e.g. physiological and phenological) are three basic groups of input data that enter into the model for the estimation of O3 flux to the vegetated surfaces (Büker et al. 2012). The stomatal conductance (Gsto) is one of the GPS Latitude Longitude 49°09'08'' N 20°17'19'' E 49°10'30''N 20°14'48'' E 49°11'21'' N 20°14'02'' E 49°15'00'' N 20°09'25'' E Stará Lesná SL Start STA Skalnaté Pleso SP Podmurá PDM South transect Skalnatá valley area Experimental site CODE North transect Tatr. Javorina area Kolové pleso KP 49°13'22'' N 20°11'27'' E Transect Aspect S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 most important and key parameters of the DO3SE model. The detailed description of the algorithm of Gsto calculation is given in the manual for modelling and mapping of the critical level exceedance (UN-ECE 2004). The stomatal flux of O3 (Fst) is modeled using an algorithm incorporating the effects of meteorological conditions (air temperature, vapour pressure deficit, light); soil and plant water (soil water potential, available water content); plant phenology and O3 concentration on the maximum stomatal conductance measured under the optimal conditions. Fst is the instantaneous flux of O3 through the stomata pores per unit projected leaf area (PLA) and refers specifically to the sunlight leaves at the top of the canopy. As there is strong biological support for the use of a threshold to represent the detoxification capacity of the trees (Karlsson et al. 2007), the expert judgement was used to set Y to 1 nmol m2 PLA s1 for the forest trees (Mills et al. 2011). The model calculation of the stomatal flux is based on the assumption that the concentration of O3 (nmol m3) at the top of the canopy c (z1) measured in the tree height (z1) represents a reasonable estimate of O3 concentration at upper surface of the laminar layer. Stomatal O3 flux Fst (nmol m2 PLA s1) is given by (UN-ECE 2004): Fst = c(z1) * Gsto * (rc / (rb + rc)) [1] where Gsto is the stomatal conductance for O3 (m s1), rb and rc are the quasi-laminar resistance and the leaf surface resistance (s m1), respectively. PLA is the abbreviation of Projected Leaf Area. The stomatal conductance can be calculated as: Gsto = gmax * fphen * flight * max {fmin, (ftemp * fVPD * fSWP)} [2] where gmax is the species-specific maximum stomatal conductance (mmol O3 m2 PLA s1), f(phen, light, min, temp, VPD, SWP) are the parameters determining the effect of the environment and phenophase on the stomatal conductance. The detailed description of the algorithm and derivation of the physical relationships for the final calculation is given in the manual for modelling and mapping of CLef level exceedance (Mills et al. 2011). The phytotoxic ozone doses (POD Y) is the accumulated value of the stomatal fluxes that exceed the threshold Y nmol m2 s1 during the vegetation season. It is calculated according to the formula: PODY = (1; n) [Fst Y] [3] for Fst Y with the accumulation of the hourly stomatal O3 flux during the whole vegetation season (defined for the tree species and year of the assessment). Fst is the hourly mean stomatal O3 flux (nmol m2 s1) and n is the number of hours within the accumulation period. The threshold Y is defined as species-specific, the actual value for forest trees is proposed to 1 nmol m2 PLA s1, the CLef of PODY is proposed to be 8 mmol m2 PLA for spruce (evergreen coniferous) with expected biomass increment reduction of 4 and 2% respectively (Mills et al. 2011). Besides PODY, the exceedance of CLec of exposition index AOT40 was calculated for all experimental sites. The AOT40 for forests is the accumulated excess of the hourly ozone concentrations above 80 µg m³ between 8:00 and 20:00 CET over the period AprilSeptember (Directive 2008/50/EC). This indicator quantifies only the ozone exposure, i.e. not the effective ozone uptake by (and therefore the damage caused to) vegetation. In this study, AOT is the sum of the concentrations over the threshold value X calculated for the daily hours during the vegetation season according to the equation: AOTX = (1; n) [C X] [4] for C X, where C is the hourly mean O3 concentration (ppb), n is the number of daily hours in the accumulation period, and X is the threshold value for forest ecosystems being 40 ppb. CLec of AOT40 was set to 5,000 ppb h (Directive 2008/50/EC). In the past, the value 10,000 ppb h was used. The exceedances of CLef for POD1 and CLec for AOT40 are calculated for the main tree species Norway spruce (Picea abies L. Karst.). The parameterisation of DO3SE model reflects the recommendations in different scientific papers, the generic values are also given in manual ICP Modelling and Mapping (UN-ECE 2010), for some of them it is possible to assess by field measurement to be species specific and also site specific. More specific and detail information about model parametrisation is included in the Appendix. 3. Results 3.1. Meteorological data and weather conditions Information on the development of meteorological parameters is important not only for the interpretation of the measured ozone data but also as key input into the model of stomatal ozone fluxes. In the High Tatra Mts., growing season 2014 (GS 2014) started after the snowmelt (March/ April) and depending on the altitude continued until the late autumn (October/November). The statistical characteristics of the hourly weather data measured at the selected field sites in the High Tatra Mts. from April to October 2014 are included in the Table 2. The mean air temperature varied in interval from 7.5 to 12.0 °C and reached maxima up to 30 °C. Values were in line with the normal course of climate data (Fig. 2). The calculated values of the vapour pressure deficit (VPD) were under the limit level (VPD_min, 3.00 kPa) for the minimal stomatal conductance (Fig. 2) that illustrates the favourable air humid conditions for the stomatal flux. The precipitation sums varied between 918 and 1,370 mm depending on the altitude of the site (Table 2). During the given GS period, the extraordinary weather events occurred. In May there was intensive heavy rain for two days and there fell about 100200 mm. The windstorm at high altitudes (the maximum observed gust has achieved value of 42 m s1) resulted in flooding and forest windfall, especially in the NW area above the Podmurá experimental site (PDM). On the other hand, the SE foothill area was affected by an exceptional long dry event in June. A rainless or light rain period lasted 38 days from 22th May to 28th June with a very low precipitation sum of 19 mm at the Stará Lesná experimental site. The next wet event started on 29 th June and continued for the next 34 days. During this period, the total S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 amount of precipitation reached a high value of 295 mm. July was a very wet month with a mean monthly temperature slightly above normal in the High Tatra Mts. as well as in whole territory of Slovakia. The weather at the end of summer and during autumn was relatively normal without unusual events. Frequently, the mean hourly wind speed values were up to a level of 5 m s1 (Fig. 2), median ranged from 0.7 to 1.9 m s1 (Table 2). For GS period, the sums of global radiation varied between the values from 542 kWh m2 measured in the NW area (Kolové pleso) to 848 kWh m2 observed in the SE area (Stará Lesná). The mean air pressure varied from 82.3 to 92.4 kPa and corresponded to the altitudinal position of the experimental sites. 3.2. Ozone data The mean O3 values at the study sites aggregated over GS 2014 fluctuated from 30.9 to 44.1 ppb (Table 3). Prevailing humid weather in the summer of 2014 influenced the O3 formations in the atmospheric boundary layer, therefore the O3 concentrations for GS 2014 was relatively low. According to data from the Slovak air quality monitoring network (SHMI and ME SR 2015), the mean O3 concentrations for GS 2014 were lower then those in GS 2003 when the summer O3 event occurred (Bicárová et al. 2005) likely due to the heatwave and extraordinary drought in Europe (Fiala et al. 2003). Generally, by many physiological studies it was approved that the light causes plant stomata to open and darkness to close. At the sites under the altitude of 1,600 m a.s.l., the mean O3 concentrations during the hours of sunlight (i.e. between 0717 h, when global radiation >50 W m2) were higher about 3090% than O3 mean concentrations during the night and weak sunlight hours (18 06 h). These results suggest relevant stomatal O3 uptake into forest vegetation during daylight hours. On the contrary, at the high altitude site of Skalnaté Pleso (1,778 m a.s.l.) the values of ozone concentrations were higher by approximately 1.7 ppb during the nights in comparison to the sunlight part of day. Nevertheless, the mean O3 values for both sunlight and night part of day at this site exceeded a level of 40 ppb. Maximal hourly O3 concentrations occurred at sites on the northern slope (75.7 88.0 ppb) were higher in comparison with sites on the southern slope (70.5 78.1 ppb). Lower O3 maxima on south-facing slope may be associated with large deforestration and reduction of biogenic O3 precursors after wind disaster (Bicárová et al. 2015). stomatal conductance was minimal with the exception of June at the foothills represented by the Stará Lesná site. Generally, the stomatal conductance gradually increases as the temperature increases reaching a peak and then gradually declines as the temperature increases beyond the optimum, whilst the stomatal conductance increases rapidly as light levels increase, reaching a maximum at relatively low light levels and maintaining that maximum as light level increase further (UN-ECE 2004). DO3SE model estimation of Fst for the experimental sites in the High Tatra Mts. (Table 5) showed that the mean Fst values for GS 2014 were over the threshold value Y of 1 nmol m 2 PLA s 1. Nearly twice higher mean Fst calculated for the sunlight part of a day (0717 h) suggests intensive stomatal O3 uptake to the forest vegetation during the photosynthetic process. The elevation profile of mean values of O3, Gsto and Fst (Fig. 3) illustrates great increase of O3 concentration with altitude that is in contrast to slightly decrease of Gsto and nearly unchanged Fst. Range Tmin-Tmax Topt SP KP STA PDM SL Avg 10 20 Ts [°C] Opt. range VPD 0.8 0.6 0.4 0.2 0.0 0 1 2 VPD [kPa] 1.0 3 SP KP STA PDM SL Avg KP PDM 3.3. Plant-specific parameters and POD1 The descriptive statistics of Gsto data estimated by DO3SE model for all 5 experimental sites in the High Tatra Mts. during GS 2014 are included in Table 4. The modeled Gsto values reached maxima up to 115 mmol m 2 s 1. Over the GS 2014, Gsto mean ranged between 21 and 28 mmol m2 s1, during the sunlight hours (0717 h) mean values were nearly twice higher. Night-time mean Gsto did not exceed level of 10 mmol m2 s1. As the growing season of 2014 was mostly humid the impact of water stress on plant SL STA SP Avg 0.0 0 5 10 WS [m s1] 15 20 Fig. 2. Cumulative frequency distribution of hourly mean air temperature (Ts), vapour pressure deficit (VPD) and wind speed (WS). S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 Table 2. Statistics of hourly meteorological data measured at experimental sites for growing season (GS), April October 2014. Experimental plot Altitude Air temperature Ts [°C] Minimum Maximum Median Mean Standard deviation Vapour Pressure Deficit VPD [kPa] Maximum Median Mean Standard deviation Precipitation P [mm] Sum for GS period Median Mean Standard deviation Wind speed WS [m s-1] Maximum Median Mean Standard deviation Global radiation R [kW m-2] Sum for GS period Monthly maximum Median Mean Standard deviation Air Pressure Pa [kPa] Minimum Maximum Median Mean Standard deviation SL 810 m asl STA 1,150 m asl Meteorological variables -3.6 27.2 10.5 10.5 5.3 2.153 0.071 0.209 0.302 917.6 377.2 438.9 306.4 16.1 1.9 2.4 1.9 552 100 78 79 22 87.1 90.1 88.7 88.7 0.5 SP 1,778 m asl PDM 1,100 m asl KP 1,570 m asl -2.9 28.4 12.2 12.0 5.8 2.536 0.174 0.342 0.386 749.1 342.7 382.5 252.5 13.7 1.5 1.9 1.3 848 156 120 121 35 90.9 93.8 92.4 92.4 0.5 -5.6 21.8 7.6 7.5 4.6 1.560 0.151 0.228 0.227 1,286.0 624.2 643.5 427.2 20.6 2.0 3.0 2.8 744 140 117 106 28 80.8 83.6 82.4 82.3 0.5 -4.0 26.5 9.5 9.4 5.8 2.466 0.079 0.232 0.327 1,337.0 779.3 717.6 437.6 8.6 0.7 1.0 0.8 657 119 95 94 22 87.7 90.6 89.1 89.2 0.5 -3.5 24.9 7.8 7.9 5.0 2.217 0.140 0.231 0.262 1,370.6 760.2 696.0 460.5 6.0 0.7 0.8 0.5 542 106 77 77 21 82.8 85.3 84.1 84.1 0.4 Table 3. Statistics of hourly O3 data for growing season (GS), April October 2014. Experimental site Altitude Minimum Maximum Median Mean Standard deviation Sunlight daily (0717 h) Minimum Maximum Median Mean Standard deviation Night and weak sunlight hours (1806 h) Minimum Maximum Median Mean Standard deviation SL 810 m asl 4.4 77.1 30.5 30.9 12.8 6.1 77.1 38.0 37.4 10.8 4.4 65.6 23.5 25.3 11.8 STA SP 1,150 m asl 1,778 m asl O3 concentration (023 h) [ppb] 3.2 10.6 70.5 78.1 31.1 44.3 31.7 44.1 11.5 8.2 7.1 70.5 37.1 36.6 10.8 3.2 62.6 26.5 27.5 10.4 14.9 78.1 43.5 43.2 8.4 10.6 70.8 45.1 44.9 8.0 PDM 1,100 m asl 2.0 88.0 29.5 29.5 15.8 4.4 88.0 40.2 39.1 13.0 2.0 73.4 17.4 21.4 13.2 KP 1,570 m asl 5.9 75.7 33.0 33.7 11.1 10.1 75.7 39.1 39.5 9.6 5.9 63.6 27.7 28.8 9.8 S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 Table 4. Statistics of stomatal conductance Gsto data estimated by DO3SE model for growing season (GS), April October 2014. Experimental site Altitude Stomatal Conductance Gsto [mmol m2 s1] All daily hours (023 h) Maximum Median Mean Standard deviation Sunlight daily hours (0717 h) Maximum Median Mean Standard deviation Night and weak sunlight hours (1806 h) Maximum Median Mean Standard deviation SL 810 m asl STA 1,150 m asl SP 1,778 m asl PDM 1,100 m asl KP 1,570 m asl Table 5. Descriptive statistics of stomatal Fst flux of O3 estimated by DO3SE model for growing season (GS), April October 2014. Experimental site Altitude SL 810 m asl STA 1,150 m asl Stomatal O3 flux Fst (nmol m2 PLA s1) 5.78 0.00 1.18 1.55 5.69 2.55 2.26 1.55 5.78 0.00 0.27 0.78 SP 1,778 m asl PDM 1,100 m asl KP 1,570 m asl All daily hours (023 h) Maximum Median Mean Standard deviation Sunlight daily hours (0717 h) Maximum Median Mean Standard deviation Night and weak sunlight hours (1806 h) Maximum Median Mean Standard deviation O3_ppb 2 1 Gsto [mmol m s ] 60 Fst 2 1 nmol m PLA s O3 (023h) Threshold Y H [m a.s.l.] Fig. 3. Altitudinal relation of O3 concentration (ppb), stomatal conductance (Gsto_mmol m2 s1) and stomatal flux (Fst_nmol m2 s1) in the High Tatra Mts. averaged for GS 2014 (023 hours). Gsto (023h) Polynomial regression Fs (023h) The model estimates for both AOT40 (Fig. 4) and POD1 (Fig. 5) for Norway spruce (Picea abies L. Karst) indicate the exceedance of CLec as well as CLef at all experimental sites in the High Tatra Mts. during GS 2014. Index AOT40 was increasing with the altitude and reached the values from 6.2 ppm h in Stará Lesná (810 m a.s.l.) to 10.7 ppm h at Skalnaté Pleso near the timber line (1,778 m a.s.l.). The critical threshold (CLec of 5,000 ppb h) was exceeded at each considered sites in different date. First it was at the Skalnaté Pleso site in the first half of June due to a generally higher O3 concentration for the higher altitude position. At the beginning of August, index AOT40 was above CLec at all sites. POD1 reached values from 13.6 mmol m2 PLA at site Kolové pleso (1,570 m a.s.l.) to 16.2 mmol m2 PLA at Skalnaté Pleso (1,778 m a.s.l.). The critical level CLef of 8 mmol m2 PLA recommended for the spruce protection was exceeded at all experimental plots during July, in around half of the growing season 2014. S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 Avg PDM SP STA CLec KP SL 0 4 5 6 7 month 8 9 10 POD1 [mmol m2 PLA] AOT40 [ppm h] 7 month Fig. 4. Accummulated ozone exposure index AOT40 [ppm h] and the concentration-based critical level (CLec) for effects of ozone on forests at experimental sites in the High Tatra Mts. during GS 2014. Fig. 5. Cumulative stomatal flux of ozone POD1 [mmol m2 PLA] and stomatal flux-based critical level (CLef) for effects of ozone on forests at experimental sites in the High Tatra Mts. during GS 2014. 4. Discussion Phytotoxic effects of O3 on forest vegetation are hardly distinguishable by direct methods. Based on recent epidemiological studies, Norway spruce is not clearly affected by visible O3 injury (chlorotic mottling on the needles) and may be classified as an O3-tolerant species (Nunn et al. 2002; Sicard et al. 2016). Critical levels of ozone concentrations could be described in different ways including concentration-based CLec for AOT40 and stomatal flux-based CLef for PODY that considers the stomatal conductance as the main control driver of O3 uptake by plants. Stomatal flux-based approach has not been applied yet in assessment of O3 impact on forest vegetation in Slovakia, mainly due to the extensive requirement of direct measurements and model input data. The presented results of pilot O3 measurements and model outputs of POD1 and AOT40 in the High Tatra Mts. achieved for the growing season of 2014 indicate vulnerability of forest vegetation to chronic and long-term exposure of O3 pollution in the Western Carpathian Mts. Our results are consistent with the findings of many previous research studies conducted in surrounding countries. For example, in the medium altitudes of forested mountains in Central Europe (in the Jizerské hory Mts.), the O3 exposure is also relatively high and comparable with the polluted sites in Southern Europe and in the higher altitudes (Hnová et al. 2016). On the contrary, some areas of the Carpathian Mountains, in Romania and parts of Poland, as well as the Sumava and Brdy Mountains in the Czech Republic are characterized by low European background O3 concentrations (summer season means of 30 ppb). Other parts of the Carpathians, particularly the western part of the range (Slovakia, the Czech Republic and Poland), some of the Eastern (Ukraine) and Southern (Romania) Carpathians and the Jizerske Mountains have high O3 levels with the peak values >100 ppb and seasonal means of 50 ppb (Bytnerowicz et al. 2004). In the Czech Republic, the O3 flux over a Norway spruce forest was measured by the gradient method and the results showed that the total deposition and stomatal uptake of O3 significantly decreased the net ecosystem production (Zapletal et al. 2011). As shown in our results, mean O3 concentrations are high enough to effective O3 uptake through stomata of coniferous trees supported by colder and wetter mountain climate favourable for open stomata processes. Both, simple concentration-based AOT40 and complex stomatal fluxbased POD1 values exceeded critical levels during growing season. AOT40 more reflects increase of O3 concentration with altitude while POD1 in relation to Gsto and Fst takes into account meteorological conditions. The main difference between AOT40 and POD1 was found in the date (month) of exceedance of critical levels, particularly at site Skalnaté Pleso where the CLec value was exceeded in June (at the earliest date) and the CLef value was exceeded later in July 2014. As confirmed by many researches, the high mountain regions are especially susceptible to the deposition of many industrial and agricultural pollutants undergoing atmospheric transport, through a process called orographic cold trapping (Hageman et al. 2015; Arellano et al. 2015). The influence of long-range transport of air pollutants on O3 concentration in the High Tatra Mts. was noticed e.g. during unusual drought and heatwave event in summer 2003 (Bicárová et al. 2005), when the values of O3 were significant higher then those observed within this study in wet GS 2014. The accumulated stomatal O3 uptakes calculated by model DO3SE exceeded CLef during the growing season 2014 (April-October) and indicate the risk of O3 injury to spruce forest in the High Tatra Mts. Based on our results, the application of DO3SE model in the High Tatra Mts. seems to be appropriate tool for monitoring of chronic O3 exposure, O3 deposition and stomatal O3 uptake to forest vegetation. Innovative epidemiological assessment of forest responses to O3 reflecting flux-effect relationships includes species-specific CLef for forest protection against visible O3 injury (Sicard et al. 2016). New CLef for the forest protection against the visible O3 injury was calculated for O3 highly sensitive conifer Pinus cembra. In this case, the proposed value of CLef 19 mmol m-2 represents the value POD0 accumulated for hours with a non-null global radiation (Sicard et al. 2016). However, visible injuries on the needles of many conifer spe- S. Bicárová et al. / Lesn. Cas. For. J. 62 (2016) 7788 cies, like Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), are rare and cannot yet be reliably associated with O3 in the field (Günthardt-Goerg 2001). Currently the main tree species of interest in our research are Norway spruce (Picea abies L. Karst.), mainly for its economic relevance in the model area as well as the Mountain pine (Pinus mugo Turra), creating a timberline in the High Tatra Mts. Another ecologically valuable and endemic tree in the Tatra Mountains is Swiss stone pine (Pinus cembra L.) that occupies specific, relatively small areas close to the alpine tree line and is highly protected in the whole Tatra National Park. Therefore, in the next years the research priorities linking to study of O3 effect on forest vegetation in the High Tatra Mts. will be focused on biomonitoring of conifer pine species, particularly Pinus cembra and Pinus mugo.
Journal
Forestry Journal – de Gruyter
Published: Jun 1, 2016