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Print version ISSN 0104-7760On-line version ISSN 2317-6342

CERNE vol.25 no.4 Lavras Oct./Dec. 2019  Epub Mar 30, 2020 



Konstantin Zavyalov1 

Natalya Ivanova1 

Anton Potapenko2 

Sezgin Ayan3  +

1 Botanical Garden of Ural Branch of Russian Academy of Sciences, Yekaterinburg, Russia

2 Institute of Forest of the National Academy of Sciences, Gomel, Belarus

3Kastamonu University, Faculty of Forestry, Silviculture Department, Kastamonu, Turkey


The purpose of the research is to identify the effect of soil factor on the ability of Scots pine to adapt to technogenic pollution based on comparative analysis of radial increment of the species which grows on soils of different fertility. The null hypothesis that soil fertility is a significant factor for adaptation was tested. The research area i.e. the plantation created in 1983 and exposed to pollution of aero-technogenic emissions of magnesium production Satka/Chelyabinsk Region/Russia, is located within the central part of the subzone of coniferous-broad-leaved and South-taiga coniferous forests of the Southern Urals. The analysis of annual growth rings (AGR) of Scots pine growing on soils of different fertility allowed us to estimate the effect of soil factor on the ability of Scots pine to adapt to magnesite pollution. As results of the research it was found that the differences in the AGR of Scots pine growing on soils of different fertility was statistically significant under the same level of technogenic pollution. During the investigation period (1994-2010), the AGR of Scots pine on fertile soils were significantly higher than those of on poor soils for 7 years. It was revealed that the positive effect of soil fertility on the Scots pine growth is leveled at the level of pollution exceeding 6-10 thousand tons per year of gaseous emissions and 25-30 thousand tons per year of total emissions. It was also found that soil fertility allows better adaptation of Scots pine to low temperatures, and more actively grow on sites with increasing precipitation.

Keywords: Scots pine; Forest planting; Dendrochronological analysis; Forest ecosystem; Aero-technogenic


Development of the industry leads to a progressing increase in emissions in atmospheric air. As a result, large areas of forest ecosystems have become under the influence of aero-technogenic pollution, thus, and the assessment of development of degressive tendencies and ability of organisms and ecosystems to adapt to this influence is needed. Steady management of bioresources and understanding of mechanisms of stabilization of the biosphere depends on the solution of this problem (MAITI et al., 2016). The exponential growth of these relevant studies raise the number of potential citers and therewith the probability of relevant papers to be cited (HAUNSCHILD et al., 2016). Special attention has been given to adaptation of woody plants to city conditions and industrial pollution (DISE and GUNDERSEN, 2004; SUKHAREVA, 2013; BUHARINA and DVOEGLAZOVA, 2016, MIKHAILOVA et al., 2017; MAKHNIOVA et al., 2019; MENSCHIKOV et al., 2019; POTAPENKO et al., 2019), as well as to the features of interference in the system of the ecosystem-soil during pollution (MENON et al., 2007; OROZCO-ACEVES et al., 2015; BENNETT et al., 2017). It is suggested that mineral food of plants has a positive impact on their adaptation to adverse effects of the environment (HABAROVA et al., 2015; MAITI and RODRIGUEZ, 2015).

In the recent years, the dendroindicative method of research in forest ecosystems has actively developed (ANONYMOUS, 1990a; SHIYATOV et al., 2000). Annual rings of tree species show regularities of influence of external environmental conditions, and it has allowed making existential assessment of change of forest ecosystems for many years. With this method, it is possible to reveal a negative or positive influence of various factors of the environment that hinder or improve the radial gain of tree species.

Technogenic factors in the modern world increasingly affects the ecosystem. One of the main sources of technogenic emissions to the atmosphere in the Urals, in Russia is the Plant Magnesite. The main purpose of this research was to reveal the influence of the soil factors on the ability of the Scots pine (Pinus sylvestris L.) to adapt to technogenic (magnesite) pollution. The basis of the comparative analysis of annual growth rings (AGR) in the Scots pine plantations that grow on soils of various fertility was followed. It should be noted that the plantations were even-aged, and exposed to a same level of pollution. It was hypothesized that the fertility of soils is a significant factor for adaptation of the Scots pine individuals to the pollution. The scientific novelty consists in the proof of statistical reliability of differences in the radial gain of the Scots pine, which grows on soils of various fertility at the identical level of technogenic pollution.


Investigation area

The Scots pine plantation established in 1983 was selected as the research area since it has been exposed to pollution of aero technogenic emissions of magnesite production (Satka, Chelyabinsk region, Russia, 550 05’ N, 590 03’ E) (Figure 1). The Scots pine plantation consist of 5 experimental sites (ES) with a total area of 6 hectares. In this work we studied two experimental sites No. 5 and 6 with an area of 1 and 0.5 hectares, respectively. The characteristics of experimental sites (ES) which are situated 3 km from the pollution source in moderately polluted zone on soils of various fertility, have been shown in Table 1 and 2.

FIGURE 1 Location of the investigation area. 

TABLE 1 Characteristics of the experimental sites and soil (material by MENSCHIKOV, 1985). 

ES Location of the site on the slope Aspect Slope Water nutrition Depth of humus horizon (cm) Soil texture
5 on the upper part of the slope south 3-50 feed from precipitation 5 sandy loam
6 on the lower part of the slope east 3-40 feed from precipitation, underground water 30 medium-textured loam

TABLE 2 Chemical characteristics of the soil of the experimental sites. 

ES Soil fertility рН* H2O Humus, ** % Р2О5 ** К2О** Relation* Mg++/Ca++
5 poor 8.5 3.1 56 110 2.7
6 fertile 8.3 9.5 70 170 0.9

Experimental sites are situated along the main path of the dust. The research area is characterized by continental climate with moderately cold winters and warm, sometimes hot summers. In spring, sharp differences from negative to positive temperatures are characteristic. The vegetation period begins in late April. Along with it, in May and even in June, it is frequently cold weather connected with the Arctic air. The cold snap quite often is followed by plentiful snow. The late spring frosts are noted at the end of May and the beginning of June while the first autumn frosts usually occur in early September. The fall season is quite warm while the early autumn is characterized, as a rule, by steady clear weather. Average annual air temperature is 0.7 0C. The total annual rainfall is 555 mm in average. The highest amount of precipitation occurs during the summer period (about 45% of the annual precipitation, mostly in July) whereas in winter their quantity decreases sharply (26% of the annual precipitation, the lowest in February). The data of the meteorological station, which is located 40 km from the source of emissions of Zlatoust, were used (ANONYMOUS, 1990b). According to B.P. Kolesnikov’s (1969) district division, the study area belongs to the central part of the sub band of coniferous and broad-leaved, and South-taiga coniferous forest zones of South Ural.


Breast height diameters (cm) of trees on sample plots in each experiment sites were measured at 1.3 m above the ground with an accuracy of 0.1 cm. Height of trees was measured using a Haglof altimeter with a precision of 0.20. Comparisons were made using the F-test for the height and diameter measurements obtained from the treatments. Life expectancy of needles was determined by visual assessment of shoots based on the number of interned internees. Escape from fully preserved needles taken equal to one, with partially preserved one-tenth of the unit. The age limit was determined by summing all values. Observations were made on 15-20 tree shoots in the upper third of the tree crown (GRUBER, 1988). Crown defoliation and crown condition, as well as damage to the stand, of each tree was recorded as outlined in Menschikov (2001). This technique was described in detail in our previous research (ZAVYALOV et al., 2018).

The forest stand damage index on the site was calculated as the average value of the categories (classes, points) of the state from 100 to 120 main trees counted on the experimental site using the equation 1, where: n 1-6 - Number of trees I, I - IV category (damage classes); K 1-6 - The points of the living condition of the categories of trees corresponding to the category number (damage class); N - The total number of recorded trees on the sample area.

lp=n1K1+n2K2++n6K6N (1)

In mixed stands, the damage index was determined separately for each tree species. Then, a general index in average was calculated for each stand.

The core samples were taken using the Swedish increment borer at about 30 cm height from two root necks from each tree. Collecting, transportation and preprocessing of cores were carried out with standard techniques, which are well accepted in dendrochronology studies (ANONYMOUS, 1990a; SHIYATOV et al., 2000). Measurement of width of annual rings was conducted by the measuring LINTAB 6 complex with an accuracy of 0.01 mm. All annual growth rings were cross-dated visually in TSAP-WIN package (RINN, 1996). For the analysis, radial increment from 1994 to2010 were used. The statistical relationships between the radial growth of the Scots pine and fertility of soils were tested using the analysis of variance (ANOVA), and correlation analyses at p<0.05 (KHALAFYAN, 2010). Calcium and magnesium metals from the soil were extracted with acetate-ammonium buffer solution. Concentrations of calcium and magnesium were determined using an atomic absorption spectrometer. Phosphorus and potassium were extracted from the soil using ammonium carbonate. Concentrations of potassium were determined using an atomic absorption spectrometer. Concentrations of phosphorus were determined using a photo electrocolorimeter. pH was determined on the ionometer. The method of determination of organic matter is based on the oxidation of organic matter with a solution of potassium bicarbonate in sulfuric acid and the subsequent determination of trivalent chromium equivalent to the content of organic matter on a photo electro colorimeter.


The study of the influence of magnesite pollution on the state and growth of the Scots pine has been carried out since 1984. Long-term study of this pollution has shown that influence of emissions of magnesite pollution leads to decrease in growth and deterioration in the state of both mature natural pine forest stands (ZAVYALOV, 2015), and forest planting, which grow 3 km from the pollution source on soils of various fertility, are studied for Pinus sylvestris L., Larix sukaczewii Dylis, Betula pendula Roth (ZAVYALOV and MENSCHIKOV, 2016; ZAVYALOV et al., 2018), decrease in elevated biomass of Betula pendula Roth (ZAVYALOV and MENSCHIKOV, 2010), increase in xeromorphy of leaves and Mg in leaves (ZAVYALOV, 2013), weak influence of the pollution on sowing qualities of seeds of Pinus sylvestris L. (MOHNACHEV et al., 2013) and on natural regeneration of Pinus sylvestris L. (MOHNACHEV et al., 2018), but noticeable decrease in radial gain in this tree species (ZAVYALOV, 2018). In the course of work, the zero hypothesis that the fertility of soils is a significant factor for adaptation of the Scots pine to pollution was supported. As it has been noted, forest stands on rich soils have the best height and diameter growth (Table 3). The study was also devoted to check of this hypothesis on statistical reliability.

TABLE 3 Indicators of experimental cultures of Scots pine. 

ES Diameter (cm) Height (m) Average index of damage Term of needles life Defoliation
5 7.2±0.33 6.9±0.20 2.66±0.08 3.4±0.07 45±2.04
6 9.7±0.75 7.2±0.49 3.13±0.18 2.8±0.11 47±4.72

The dispersive analysis, which was carried out every year during the study, has revealed statistical reliability of differences in radial growth of Scots pine in 1994, 1997, 1998, 1999, 2000, 2001 and 2002. These years’ radial gains of Scots pine on rich soils were bigger in comparison with the gain on poor soils (Table 4). It exhibits the statistical importance of the factor of fertility for adaptation of plants to pollution.

TABLE 4 Dispersion analysis of the dependence of the radial growth of Scots pine on soil fertility . 

Nº ES Average AGR -95% +95% F-test** (1.77) p
1994 year
5 251 232 271 11.42 0.0011*
6 320 276 365
1995 year
5 317 294 341 0.34 0.56
6 331 285 376
1996 year
5 255 238 271 0.64 0.43
6 268 232 304
1997 year
5 200 185 215 16.46 0.0001*
6 266 229 303
1998 year
5 129 115 143 16.37 0.0001*
6 192 157 227
1999 year
5 104 91 117 29.84 0.0001*
6 194 152 237
2000 year
5 94 81 107 64.19 0.0001*
6 241 189 292
2001 year
5 91 76 106 67.72 0.0001*
6 239 193 285
2002 year
5 133 113 154 23.29 0.0001*
6 228 195 261
2003 year
5 182 156 207 3.85 0.05
6 230 185 275
2004 year
5 244 210 279 0.36 0.55
6 225 174 276
2005 year
5 280 249 310 0.16 0.69
6 268 216 320
2006 year
5 210 183 237 0.02 0.90
6 207 169 245
2007 year
5 279 244 313 1.01 0.32
6 246. 191 301
2008 year
5 238 204 271 0.34 0.56
6 219 165 274
2009 year
5 250 222 277 0.57 0.45
6 229 176 282
2010 year
5 172 148 195 0.24 0.63
6 160 116 205

Note: * - statistically significant p<0.05 was observed, **F-test is a Fisher test (the critical value of the Fisher test is given in brackets). If the actual value of F is bigger than or equal to the critical (standard) value of F, the differences between the samples are statistically significant.

The lack of reliable differences in growth in other years allows carrying out the analysis of restrictions of adaptation ability of Scots pine, connected with other external natural and technogenic factors. For these purposes, we have carried out the correlation analysis, and monitored the influence of the external factors on the level of differences in radial gains of Scots pine growing on poor and rich soils. Coefficients of Spearman correlations for significance value of distinctions (the values p given in table 4), and a number of natural and technogenic factors are calculated. The results of the correlation analysis are given in table 5.

TABLE 5 Correlation analysis of factors influence on the level of differences in the radial growth of Scots pine growing on poor and rich soils. 

Factor Spearman correlation coefficient P
Total air pollutants 0.63 0.006*
Gaseous air pollutants 0.57 0.016*
Average temperatures in May-August 0.64 0.005*
Average temperatures for June-August 0.41 0.099
Sum of positive temperatures 0.61 0.009*
Average monthly precipitation of the calendar year -0.55 0.021*
Amount of precipitation in the calendar year -0.55 0.021*
The average monthly precipitation of the growing year -0.34 0.183
Average monthly precipitation from September of the previous year to August of the current year -0.54 0.026*
Amount of precipitation from September of the previous year to August of the current year -0.54 0.026*

Statistically significant correlations (p<0.05) were shown by emissions - general and gaseous ones (technogenic factors), average temperatures in May-August, the sum of positive temperatures, average monthly rainfall and the sum of precipitation a year, average monthly rainfall and the sum of precipitation from September of the previous year to August of the current year (Table 5).

We investigated the effects of emissions in more detail and found that the significant differences in the growth of pine on poor and rich soils were detected only when the level of pollution is less than 6,000-10,000 tons. If contamination is above this level, the differences in growth are leveled. However, this pattern was not examined in certain years with weather factors (i.e., 1995, 1996 and 2010). In 1995, there was a large emission to atmosphere of dust (KUZMINA and MENSCHIKOV, 2015). These emissions affected radial growth not only in 1995 but also in 1996. It should be noted that 2010 was very hot (ANONYMOUS, 1990b).

We performed a similar analysis for total air pollutants. The threshold values of total air pollutants were 25-30 thousand tons.


The comparative analysis of AGR of Scots pine plantations which grow on soils of various fertility, has allowed the estimation of the influence of the soil factor on ability of the Scots pine to adapt to technogenic (magnesite) pollution (Satka, Chelyabinsk region). The statistical reliability of differences in AGR of Scots pine was obtained. For the studied 17-year summer period (1994-2010) for 7 years AGR of the Scots pine, growing on fertile soils, were relatively higher than the pine growth on poor soils. It was revealed that, at the pollution level exceeding 6-10 thousand tons per year of gaseous emissions and 25-30 thousand tons per year of general emissions, the positive effect of fertility of soils on growth of Scots pine is leveled. The results obtained are of practical importance for reclamation of man-made landscapes.


The work was carried out within the framework of the state task of the Botanical garden of the Ural branch of RAS. The authors would like to thank Assoc. Prof. Dr. Ferhat KARA, Kastamonu University, Faculty of Forestry, in Turkey and Prof. Dr. Sergey MENSCHIKOV Botanical Garden Ural Branch of Russian Academy of Sciences, Yekaterinburg, Russia, for their contributions to the paper.


ANONYMOUS. Methods of dendrochronology, Application in the environmental sciences (eds. E.R. Cook, L.A. Kairiukstis). Dordrecht - Boston - London: Kluwer Acad. Publ., 394 р. 1990a. [ Links ]

ANONYMOUS. Scientific-applied Handbook on the USSR climate, Series 3. Multiyear data. kN. 1, part 1-6. Issue. 9. L.: Hydrometeoizdat, 557 p. 1990b. [ Links ]

BENNETT, J. A.; MAHERALI, H.; REINHART, K. O.; LEKBERG, Y.; HART, M. M.; KLIRONOMOS, J. Plant-soil feedbacks and mycorrhizal type influence temperate forest population dynamics, Science, 355 (6321): 181-184. 2017. [ Links ]

BUHARINA, I. L.; DVOEGLAZOVA, T. M. Bioecological features of herbaceous and woody plants in urban plantations, Izhevsk, Udmurt University Publishing House, 184 p. [In Russian]. 2010. [ Links ]

DISE, N. B.; GUNDERSEN, P. Forest ecosystem responses to atmospheric pollution: Linking comparative with experimental studies, Water, Air, & Soil Pollution: Focus, 4 (2): 207-220. 2004. [ Links ]

GRUBER, F. Die Anpassung der fichtenkrone (Picea abies (L.) Karst.) uber die triebbildungsarten. Schweizerische Zeitschriftfür Forstwesen, 139 (3): 173-201. 1988. [ Links ]

HABAROVA, E. P.; FEKLISTOV, P. A.; KOSHELEVA, A. E. Contents of mineral elements in the dying off needles of Scotch pine on drained areas, Forestry Bulletin, 19. (2): 15-20 (In Russian). 2015. [ Links ]

HAUNSCHILD, R.; BORNMANN, L.; MARX, W. Climate change research in view of bibliometric, PLoS ONE. 11 (7): e0160393. 2016. [ Links ]

KHALAFYAN, A. A. STATISTICA 6. Statistical data analysis: a tutorial. M.: «Binom-Press», 528 p. 2010. [ Links ]

KOLESNIKOV, B. P. Forests of Chelyabinsk region, Forests of the USSR, 4:125-157. 1969. [ Links ]

KUZMINA, N.A.; MENSHCHIKOV, S. L. Impact of agrotechnogenic emissions of magnesite production on the chemical composition of snow water and soil in dynamics, Izvestia Orenburg State Agrarian University, 56 (6) 192-195 (in Russian). 2015. [ Links ]

MAITI, R.; RODRIGUEZ, H. G. Mystry of coexistence and adaptation of trees in a forest ecosystem, Forest Research, 2015. 4:e120. 2015. [ Links ]

MAITI, R.; RODRIGUEZ, H.G.; IVANOVA, N. S. Autoecology and ecophysiology of woody shrubs and trees: Concepts and applications. John Wiley & Sons, 352 pp. 2016. [ Links ]

MAKHNIOVA, S.; MOHNACHEV, P.; AYAN, S. Seed germination and seedling growth of Scots pine in technogenically polluted soils as container media, Environ. Monit. and Assess.191(2) 113. 2019. [ Links ]

MENON, M.; HERMLE, S.; GÜNTHARDT-GOERG, M.S.; SCHULIN, R. Effects of heavy metal soil pollution and acid rain on growth and water use efficiency of a young model forest ecosystem, Plant and Soil, 297: 171-183. 2007. [ Links ]

MENSCHIKOV, S.; KUZMINA, N.; AYAN, S.; ÖZEL, H. B. Effects of mining, thermal, industrial plants on forests land and rehabilitation practices in Ural Region in Russia, Fresenius Environmental Bulletin, 28 (2A) 1511-1521, 2019. [ Links ]

MENSCHIKOV, S. L. Research of ecological features of growth and reasons for agrotechnology of creation of cultures of coniferous breeds in the conditions of magnesite dust, 1985. 20 p., avtoref. diss. cand. agricult. Sciences. Sverdlovsk, [ Links ]

MENSCHIKOV, S. L. Methodical aspects of assessment of damage to forests damaged by industrial emissions in the Central Ural Mountains. The forests of the Urals and economy in them. Yekaterinburg: Ural State Forest Engineering University, 21: 243-251 (in Russian). 2001. [ Links ]

MENSCHIKOV, S. L.; KUZMINA, N. A.; MOHNACHEV, P. E. Influence of atmospheric emissions of magnesite production on soils and snow cover, Izvestia of Orenburg State Agrarian University, 5 (37): 221-224. 2012. [ Links ]

MIKHAILOVA, T. А.; AFANASIEVA, L. V.; KALUGINA, O. V.; SHERGINA, O. V.; TARANENKO, E. N. Changes in nutrition and pigment complex in pine (Pinus sylvestris L.) needles under technogenic pollution in Irkutsk region, Russia. Journal of Forest Research , 22 (6): 386-392. 2017. [ Links ]

MOHNACHEV, P. E.; MAKHNIOVA, S. G.; MENSCHIKOV, S. L. Features of reproduction of the Scotch pine (Pinus silvestris L.) in the conditions of pollution by magnesite dust, Izvestia of Orenburg State Agrarian University . 3 (41) 8-9. 2013. [ Links ]

MOHNACHEV, P. E.; MENSCHIKOV, S. L.; MAKHNIOVA, S. G.; ZAVYALOV, K. E.; KUZMINA, N.; POTAPENKO, A.; AYAN, S.; LAARIBYA, S. Scotch pine regeneration in magnesite pollution conditions in South Ural, Russia. SEEFOR, 9 (1): 55-60. 2018. [ Links ]

OROZCO-ACEVES, M., STANDISH, R.J., TIBBETT, M. Soil conditioning and plant-soil feedbacks in a modified forest ecosystem are soil-context dependent, Plant and Soil , 390: 183-194. 2015. [ Links ]

POTAPENKO, A., BULKO, N., KOZLOV, A., MOHNACHEV, P., ZAVYALOV, K., KUZMINA, N., AYAN, S. Influence of scotch pine (Pinus sylvestris l.) plantations on near and far territories of Chernobyl anthropogenic factors, Forestry Ideas, 25 (2) 58: 301-313. 2019. [ Links ]

RINN, F., TSAP. Reference manual. Version 3.0. Heidelberg, 263 p. 1996. [ Links ]

SHIYATOV, S. G.; VAGANOV, E. A.; KIRDYANOV, A. V.; KRUGLOV, V. B.; MAZEPA, V. S.; NAURZBAEV, M. M.; HANTEMIROV, R. M. Methods of dendrochronology. Part 1. Basics of dendrochronology. Collection and receipt of wood-ring information: educational and methodical manual. Krasnoyarsk: Krasnoyarsk state University, 80 p. 2000. [ Links ]

SUKHAREVA, T. A. Spatio-temporal dynamics of microelement composition of conifers and soils under industrial pollution, Bulletin of higher educational institutions//Lesnoyzhurnal. 6:19-28 (In Russian). 2013. [ Links ]

ZAVYALOV, K. E. Morphology and chemical composition of leaves of pilot cultures of the silver birch (Betula pendula Roth.) in the conditions of magnesite pollution, Izvestia of Orenburg State Agrarian University , 3(41): 230-232. 2013. [ Links ]

ZAVYALOV, K.E. Sostoyaniye of pine forest stands of a green zone Satka, subject to aero technogenic emissions of magnesite production. Izvestia of Orenburg State Agrarian University , 6 (56): 57-59. 2015. [ Links ]

ZAVYALOV, K. E. The response of radial growth of Pinus silvestris L. in the experience of recultivation of technogenic-disturbed lands Satka city, Ecology and Industry of Russia, 22 (4): 60-63. 2018. [ Links ]

ZAVYALOV, K. E.; MENSCHIKOV, S. L. Experience of recultivation measures for reforestation of disturbed lands of Satka industrial complex. Ecology and Industry of Russia , 20 (12): 36-38. 2016. [ Links ]

ZAVYALOV, K. E., MENSCHIKOV, S. L. Overground phytomass of pilot cultures of the birch in conditions of magnesite dust pollution, Izvestia of Orenburg State Agrarian University , 4 (28): 27-30. 2010. [ Links ]

ZAVYALOV, K. E.; MENSHIKOV, S. L.; MOHNACHEV, P. E.; KUZMINA, N.; POTAPENKO, A.; AYAN, S. Response of Scots pine (Pinus sylvestris L.), Sukachyov’s larch (Larix sukaczewii Dylis), and Silver birch (Betula pendula Roth) to magnesite dust in Satkinsky industrial hub, Forestry Ideas , 24 (1): 23-36. 2018. [ Links ]


1The null hypothesis of the research is to test whether soil fertility in technogenic contaminated areas is an important factor for adaptation of Scots pines.

2Different soil fertility allowed us to estimate the effect of soil factor on the ability to adapt to magnesite pollution.

3The annual growth rings of Scots pine growing on soils of different fertility were significantly different under the same level of technogenic pollution.

4Soil fertility allows better adaptation of Scots pine to low temperatures, and more actively grow on sites with increasing precipitation.

Received: October 15, 2019; Accepted: November 05, 2019

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