Ecological adaptations among spruce species along an environmental gradient in urban areas

Knowledge about current state of the trees in urban areas may be important for foresting and green planting of city landscapes and for improving environmental quality in these areas. The object of this study were to screen a range of morphometric, physiological and biochemical parameters among species of the genus spruce (Picea A. Dietr.) in urban areas of Kryvyi Rih City and to assess the ecological adaptations among species of the genus spruce (Picea A. Dietr.) along an environmental gradient in urban areas of Kryvyi Rih City. During 2017-2021, the 7 research plots in Kryvyi Rih City urban areas along an environmental gradient (low, moderate and high levels of the environmental impact) and 1 research plot in the background area (control) were established. The 30–40-year-old trees of indigenous spruce species (Norway spruce (Picea abies (L.) Karst.)) and non-native spruce species (Colorado blue spruce (Picea pungens var. ‘Glauca’)) were investigated. The morphometric characteristics of trees, vitality of trees and chlorophyll a, chlorophyll b content in needles were studied. The results showed that in background area the tree height (14.5-15.1 m and 11.7-12.5 m for Norway spruce and Colorado blue spruce), diameter at breast height (25.3-28.1 cm and 24.6-27.2 for Norway spruce and Colorado blue spruce), chlorophyll a content (0.75-1.04 mg/g of wet weight and 0.96-1.24 mg/g of wet weight for Norway spruce and Colorado blue spruce) and chlorophyll b content (0.33-0.41 mg/g of wet weight and 0.42-0.50 mg/g of wet weight for Norway spruce and Colorado blue spruce) were typical of mature 30-40-year-old spruce trees. In Kryvyi Rih City urban areas the ecological stress along an environmental gradient decreased the values of growth, vitalyty and photosynthetic activity of the trees by 15-50%. Colorado blue spruce trees (non-native species) exhibit greater ecological tolerance and ecological adaptations than Norway spruce trees (indigenous species). Colorado blue spruce is less sensitive to environmental impact and have a better ecological adaptive balance of pigment content than Norway spruce. Our results confirm that from a sustainable development of the urbane areas perspective it is necessary to using the Colorado blue spruce for greene planting.


Introduction
Today, the state of the environment in industrial cities is very critical, causes concern and requires practical measures to improve it [1][2][3][4][5].The trees play an important role in improving the quality of the urban areas.Landscaping of these areas with woody plant species is an important practical measure for the implementation of sustainable development in current cities [5][6][7][8][9].Among the assortment of plants, preference is given to those with high phytoncide 1254 (2023) 012114 IOP Publishing doi:10.1088/1755-1315/1254/1/012114 2 properties [6,10,11].In particular, such plants are conifers, which clean the air of harmful substances all year round, absorbing almost all types of chemical compounds entering the atmosphere with emissions from industry, energy, motor vehicles [12][13][14][15].However, improving environmental conditions, coniferous plants themselves suffer from the negative effects of air pollutants, which leads to changes in their biological parameters, biochemical characteristics and, in general, to a decrease in their viability [6,11,16].Due to this speed of reaction to pollutants substances, plants of conifers are used as environmental indicators [5,6,10,13].
In Kryvyi Rih, one of the largest industrial cities of Ukraine, the level of atmospheric air pollution significantly exceeds the limits [10,17].Emissions from industrial enterprises and intensive traffic lead to the formation of harmful substances in the air, among which are noted: nitrogen oxides, sulfur dioxide, carbon monoxide, etc. [13][14][15].The negative impact of pollution is enhanced by adverse natural and climatic conditions, which in the steppe zone are exacerbated due to climate change, which causes global warming [17,18].It is difficult for introduced conifers to adapt to the urbotechnogenic environment of a large industrial steppe city.
Among the widespread assortment coniferous plants of Kryvyi Rih excrete out trees of spruce species, which grow all over the city in different types of plantings.In addition, they are characterized by high phytoncide activity, year-round decorativeness, attractive color of the needles [5,6,11].Considering on it, the objectives of the study were (1) to screen a range of morphometric, physiological and biochemical parameters among spruce species in urban areas of Kryvyi Rih City, (2) to assess the ecological adaptations among spruce species along an environmental gradient in urban areas of Kryvyi Rih City.

The study area
The urbane areas of Kryvyi Rih City (central part of Ukraine) was chosen for the present study.It is situated between 47°53'54" and 48°8'52" north latitude and 33°19'52" and 33°33'38" west longitude.The climate of this area is characterized by short springs, hot and dry summers and cold winters with little snowy.The monthly mean air temperature ranged from -5.1°C (in January) to 22.2°C (in July).The mean annual precipitation was from 400 to 450 mm [2,3,16].Kryvyi Rih is one of the largest industrial city in Europe, specializing in iron ore mining and production of iron ore concentrate, iron ore agglomerate, iron ore pellets, cast iron smelting and steel smelting.In this city the industrial activity (mining, processing and smelting operations) generate a lot of pollutants (dust, carbon / sulphur / nitrogen oxides, heavy metals) that is released into the atmosphere.The annual emissions air pollutants range from 400 000 to 700 000 tons per year [2,17].

Research design, data collection and sampling
In our study the 30-40-year-old trees of indigenous spruce species (Norway spruce (Picea (L.) Karst.)) and non-native spruce species (Colorado blue spruce (Picea pungens var.'Glauca' ) were investigated.A systematic random sampling design was used for selection of sampling sites.The study area was divided into two locations as control area and environmental imputed area.The territory of Kryvyi Rih Botanical Garden arboretum was used as a control (sampling site 1).The environmental imputed area was divided into sub-locations as (i) low environmental impact (sampling sites 2, 3), (ii) moderate environmental impact (sampling sites 4, 5, 6) and high environmental impact (sampling sites 7, 8).All research points were located at three Kryvyi Rih City Districts such as Ternivskyi, Pokrovskyi and Metalurhiinyi.The spatial distribution of the sampling sites is shown in figure 1. Field data were collected through direct enumeration and measurement of 30-40 trees in every sampling site [19].In each site, the tress were recorded and: (i) their diameter at 1.3 m above ground (in two perpendicular directions by a caliper); (ii) their height (by a hypsometer), (iii) the crown height and diameter (in two directions: east-west, south-north) were measured and (iv) their vital state was assessed (by Yarmishko [20]).In each site the 10 dominated trees were randomly selected.From each trees five samples of the two-year needles were sampled.After sampling, needles were combined to give one composite sample per site.The samples were stored in plastic bags in a freezer (-4 °C) before analysis [21].

Analytical methods
The concentrations of chlorophyll a and chlorophyll b in two-year needles were determined spectrophotometrically using a SF-2000 instrument according to follow methodical [22].Approximately 0.1 g crushed needles samples were soaked in 2 mL dimethyl-sulfoxide and incubated in water bath at 67°C for three hours.The absorbance of samples was measured at 665 nm (chlorophyll a) and 649 nm (chlorophyll b).
Content of chlorophylls and carotenoids was calculated using the following equations by Wellburn [23]: where A is the absorbance; Cchl a is concentration of chlorophyll a, mg/mL; Cchl b -is concentration of chlorophyll b, mg/mL.Pigment concentration was expressed as mg per g of raw weight using the following equation by Wellburn [23]: where: PC -content of pigments in needles, mg/g of raw weight; C -pigment content in extract, mg/mL; V -volume of extract, mL; H -weight of needles, g.All determination was done in four replicates for each species.

Statistical analysis
The results were statistically analysed using a descriptive statistics.The differences between mean values from environmental imputed area and control were tested by a Student's t-test for independent variables at 5% probability level (p < 0.05) [24,25].Statistical analysis was performed using Microsoft Office Excel 2003.

Results and discussion
The territory of Kryvyi Rih Botanical Garden arboretum is characterized by environmentally friendly conditions for spruce species.That is why in control plot, the basic morphometric characteristics included tree height (14.8±0.14 m and 12.1±0.22m for Norway spruce and Colorado blue spruce, respectively) and diameter at breast height (26.7±0.71cm and 25.9±0.65 for Norway spruce and Colorado blue spruce, respectively) were typical of mature spruce 30-40year-old trees and comparable to those reported by many authors [26,27].It should also be noted that in the control plot, the vitality of spruce trees was assessed as "healthy": 93.3% and 95.7% for Norway spruce and Colorado blue spruce, respectively (table 1).According to obtained results, in control site the tree height of spruce species were more and the diameter at breast height of spruce species were large than morphometric characteristics of same age spruce trees from environmental impact areas (table 1).Thus, in low environmental impact area the mean of tree height of Colorado blue spruce was statistical significance lower than the bouground value (by 11.5%).In moderate environmental impact area the means of tree height were lower than control (by 18.2% and 19.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In this area the means of diameter at breast height were statistical significance lower than mean values from bouground area (by 16.3% and 8.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In high environmental  According to obtained results, in control site the tree height of spruce species were more and the diameter at breast height of spruce species were large than morphometric characteristics of same age spruce trees from environmental impact areas (table 1).Thus, in low environmental impact area the mean of tree height of Colorado blue spruce was statistical significance lower than the bouground value (by 11.5%).In moderate environmental impact area the means of tree height were lower than control (by 18.2% and 19.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In this area the means of diameter at breast height were statistical significance lower than mean values from bouground area (by 16.3% and 8.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In high environmental impact area the means of tree height were lower than the bouground value (by 30.1% and 28.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In this area the means of diameter at breast height were statistical significance lower than control (by 21.6% and 14.9% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).
As demonstrated in table 1, in all environmental impact areas the vitality values of the all spruce species were statistical significance lower than control levels.The vitality values in Norway spruce trees were significantly lower in low environmental impact area by 15-16% (p < 0.05), in moderate environmental impact area by 17-18% (p < 0.05) and in high environmental impact area by 50-51% (p < 0.05).Colorado blue spruce alsow showed differences in vitality values but showed a more smaller amplitude.The means of tree vitality was statistical significance lower than the control value by 9.9%, 23.2% and 40.0% in low, moderate and high environmental impact areas, respectively (p < 0.05).
The needles chlorophyll concentration is an important parameter that is regularly measured as an indicator of plant metabolism, plant stress and of plant's current state in urban areas [11,[28][29][30][31].It has been found that maximum contents of chlorophyll a in needles of spruce species were in May in control site: 1.04 mg/g of wet weight and 1.24 mg/g of wet weight for Norway spruce and Colorado blue spruce, respectively (figure 2).These values were statistical significance higher than concentration of this pigment in environmental impact areas by 16.3% -20.6% (p < 0.05).The results of our study concur with the findings of previous researches.
The data of many authors in different countries indicated a higher concentrations of chlorophyll a in needles of spruce species in May [6,32].This is due to sufficient rainfall and optimal air temperature for the plant development, increasing during the next months.The lowest chlorophyll a content in needles of spruce species were found in September in high environmental impact area: 0.58 mg/g of wet weight and 0.70 mg/g of wet weight for Norway spruce and Colorado blue spruce, respectively.These values were lower than control by 21.6% and 29.3% (p < 0.05).For both species, we observed a general tendency to reduce this pigment concentration during summer and autumn, especially in September, as this period was characterized by low rainfall and air drought.In the course of five-month studies, was found a significant decline in the chlorophyll a content in needles of spruce species along an environmental gradient.But in all environmental impact areas the content of this pigment in the needles of Colorado blue spruce was a relative stability and higher than in the needles of Norway spruce.We hypothesize that Norway spruce is more sensitive to environmental impact than Colorado blue spruce.
The result of our investigation clearly indicated that minimal contents of chlorophyll b in needles were found in September in high environmental impact area (near cast iron smelting and steel smelting plants).At this site concentration of chlorophyll b was 0.29 mg/g of wet weight in needles of Norway spruce and was and 0.33 mg/g of wet weight in needles of Colorado blue spruce.These values were lower than control by 14.7% and 21.4%, respectively (p < 0.05).
During five months of our investigations, there was a significant decrease in the value of chlorophyll b concentration in the needles of both spruce species along an environmental gradient in Kryvyi Rih City urban areas.We imply that this phenomenon is determined by distance from urban roads, from ore mining and processing enterprises and from metallurgical combine.
It is known from earlier publications that environmental pollution decreased the content of chlorophyll b in needles more than the content of chlorophyll a in needles [11,32].It may reduce the activity of the photosynthetic apparatus and disrupt the plants metabolism.However, other researchers reported that chlorophyll a was to be less stable than chlorophyll b in the pigment complex of conifers in urban areas [33,34].In our research, the second variant of the dynamic changes in pigment complex of needles was confirmed: along an environmental gradient in Kryvyi Rih City urban areas more significantly decreases the content of chlorophyll a than content of chlorophyll b.
Still remain controversial the data about of the photosynthetic apparatus stability in coniferous plants under environmental effects.Some authors [35] were noted that Norway spruce and Colorado blue spruce had the same inhibition effects of the pigment complex functioning under the stress influence of the air pollution.But according to results of the our research Colorado blue spruce had a better adaptive balance of pigment content than Norway spruce.
Many authors [6,10,11,32,36,37] reported that the morphometric characteristics, vitality and intra-annual dynamics of chlorophyll content in needles of spruce species determined by climatic conditions and environmental impact level.According to our results, the maximum decrease of values of morphometric characteristics, vitality and chlorophyll content were wound in the southern part of the Kryvyi Rih City near largest in Ukraine processing, cast iron smelting and steel smelting enterprise.Finally, our results are agree with several numerous studies and key sciences publications.The obtained results of this study help to provide important information on understanding how trees of spruce species can affecting on urban ecology and urban sustainable development by temperature reduction, by reduce heat stress, by carbon storage and by promoting biodiversity.Besides, they may serve as reference levels for future studies in other urban areas at similar sites all over the world.
As in previous case, the maximum contents of chlorophyll b in needles of spruce species were in May in control site: 0.41 mg/g of wet weight and 0.50 mg/g of wet weight for Norway spruce and Colorado blue spruce, respectively (figure 3).These values were statistical significance higher than concentration of this pigment in environmental impact areas by 9.8% -18.0%(p < 0.05).

Conclusions
In the present study, the large range of morphometric characteristics, vitality and of chlorophyll content in needles of Norway spruce and Colorado blue spruce were observed.In control plot, the tree height, diameter at breast height, chlorophyll a content and chlorophyll b content were typical of mature spruce 30-40-year-old trees.Based on the obtained results, it can be concluded that spruce species is affected by environmental impact.In Kryvyi Rih City urban areas the ecological stress along an environmental gradient decreased the values of growth, vitalyty and photosynthetic activity of the trees by 15-50%.Our study demonstrated that Colorado blue spruce trees exhibit greater ecological tolerance and ecological adaptations than Norway spruce trees.Colorado blue spruce is less sensitive to environmental impact and have a better adaptive balance of pigment content than Norway spruce.Our results confirm that from a sustainable development of the urbane areas perspective it is necessary to using the Colorado blue spruce for green planting.

Figure 2 .
Figure 2. Content of chlorophyll a in needles of spruce species along an environmental gradient in Kryvyi Rih City urban areas, mg/g of wet weight, n = 5 (A -Norway spruce (Picea abies), B -Colorado blue spruce (Picea pungens var.'Glauca').1 -control site, 2-8 -environmental impact sites.Asterisks indicate that the difference between control and research sites are statistically significant, p ≤ 0.05).

Figure 3 .
Figure 3. Content of chlorophyll b in needles of spruce species along an environmental gradient in Kryvyi Rih City urban areas, mg/g of wet weight, n = 5 (A -Norway spruce (Picea abies), B -Colorado blue spruce (Picea pungens var.'Glauca').1 -control site, 2-8 -environmental impact sites.Asterisks indicate that the difference between control and research sites are statistically significant, p ≤ 0.05).

Table 1 .
Morphometric characteristics and vitality of spruce species along an environmental gradient in Kryvyi Rih City urban areas, M ± SD.
M -Mean; SD -Standard Deviation.Asterisks indicate that the difference between control and research plots are statistically significant, p ≤ 0.05.impact area the means of tree height were lower than the bouground value (by 30.1% and 28.1% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).In this area the means of diameter at breast height were statistical significance lower than control (by 21.6% and 14.9% for Norway spruce and Colorado blue spruce, respectively (p < 0.05)).