Research on Regional Plant Landscape of Industrial Cities in Henan Province

. Plant landscape is an indispensable part of the city. Regional plant landscape not only has excellent ecological benefits, but also can better show the regional characteristics and human culture of the city. Through the analysis of plant landscape in the industrial city, it is concluded that how to make better use of plants to create urban plant landscape with regional characteristics is the focus of regional plant landscape construction.


Introduction
With the rapid development of China's economy, the process of urbanization and industrialization has also been significantly accelerated. In the early stages of urban industrial development, the backwardness of industrial technology and the unreasonable development of resources caused serious environmental pollution. With the advancement of science and technology, the optimization and upgrading of the industrial structure, coupled with the increase of people's awareness of environmental protection, and increased efforts to control pollution, the air quality in industrial cities has gradually improved. This is the epitome of most industrial cities in China. The industrial cities in Henan Province mainly include Zhengzhou, Jiaozuo, and Pingdingshan etc. As an industrial city, economic development is closely related to environmental quality. Although mining mineral resources promotes economic development, it also brings many environmental pollution problems, such as air pollution and soil pollution. As we all know, plants have the function of purifying the air and protecting the environment. In the process of applying plants to create landscapes and improve the environment, industrial cities have also formed distinctive regional plant landscapes. Therefore, this research takes the industrial cities in Henan as the research object, and studies the regional plant landscapes of each city, in order to provide a reference for greening and beautifying the city.

Purification and noise reduction effects of plants on the city
The impact of plants on the air is mainly reflected in the fact that plants can absorb harmful gases, purify the air, and can also reduce noise and adjust the climate. Some plants are highly resistant to air pollution, and can also absorb and accumulate pollutants [1], thereby purifying the air and protecting the environment. For example, Nerium oleander, Sophora japonica, Cinnamomum camphora, Privet, Koelreuteria paniculata, Ginkgo, Willow, Platanus, Crape myrtle, Ailanthus altissima, Paper mulberry, Chinese rose and other tree species have high resistance to SO₂. They can be produced by absorbing and using SO₂, and Sulfate becomes a substance beneficial to plant growth. These plants usually have dense leaves, leathery leaves or waxy layers and fluff, the harmful gas is difficult to pass through [2], which can be used as the basis to select suitable anti-pollution plants for industrial cities. The high and low scattered and rich plant landscape can not only beautify the environment, but also more effectively to purify the air and reduce the noise.

Purification effect of plants on soil pollution
Plants can absorb, utilize and enrich some heavy metal elements in the soil. For example, Holly, Poplar and other tree species have a high enrichment capacity for heavy metal elements such as Cr, Zn, Cu, Pb in the soil, which can transfer the heavy metals in the soil to the aboveground parts of plants [3]. Through the centralized treatment of plant above-ground parts, it can effectively reduce soil pollution and improve soil fertility [4]. and Cultural Center for most of China's history, Henan developed many industries in ancient times and retained many ancient industrial heritages. In modern history, modern industrial cities were also born in Henan Province, such as Luoyang, Zhengzhou, and Jiaozuo [5]. Although the rise of industry has led to the rapid development of economy, but also caused urban environmental pollution, and the air pollution has become the main problem of the urban environment. In the past five to ten years, "smog" has appeared in many cities in Henan Province, and the air quality of each city in Henan Province is far behind that of other cities. In recent years, through the national policy guidance and significant efforts of governance, air quality has been significantly improved, but it has brought various aspects of impact, plant landscape is one of them. In order to create urban landscape and reduce air pollution, some anti-pollution tree species have been applied in some cities, forming a special regional plant landscape.
Henan Province is in the central plains, belonging to the transition from subtropical to warm temperate continental monsoon climate, have four distinct seasons, and enough rainfall. Henan Province is rich in plant resources, most of northern and southern plants are grow well here. The native plants in Henan mainly include Poplar, Ailanthus altissima, Sophora japonica, Willow, Paulownia, Melia azedarach, etc.
[6]. The representative plants of main industrial cities in Henan Province are shown in Table 1.

Natural conditions in Pingdingshan
Pingdingshan is in the central-southern part of Henan Province, between 33°08'-34°20' north latitude and 112°14'-113°45' east longitude. It is in the transitional zone between mountains and plains, and has the characteristics of high west and low east. Pingdingshan has a continental monsoon climate, located on the edge of a warm temperate zone and a subtropical climate, with four distinct seasons and enough sunlight and rainfall. The city's annual average total sunshine hours are about 1868-2378h, and the annual average temperature is between 14.8～15.2℃; the extreme minimum temperature is -11.3℃, and the extreme maximum temperature is 38.1℃. The average annual precipitation in the city is about 1000mm, which is suitable for the growth of most woody plants.

Social factors in Pingdingshan
Pingdingshan's industries mainly include coal mining and washing industry, chemical industry, and fuel processing industry. Relying on abundant mineral resources and a solid industrial foundation, Pingdingshan's economic development is very rapid. Although the energy model based on coal mining has driven rapid economic growth, it has also brought serious environmental pollution and climate change. The main pollution includes: when mining coal mines, heavy metal elements in coal gangue such as Cr, Hg, Pb, Cu, Zn, etc. enter the soil and cause soil pollution [7], air pollution caused by coal fly ash, automobile exhaust, sulfur oxide and dust in the atmosphere [8]. Besides, with the growth of the population of Pingdingshan, the demand for resources is also increasing, which leads to the exploitation of more resources. Whether it is human life activities or mining activities, it will inevitably emit a large amount of Carbon causes the continuous increase of carbon emissions, which in turn affects the environment and climate [9]. In the past few years, residents lived in an environment with poor air quality most of the time. Because of this, Pingdingshan's plants are mostly anti-pollution tree species, such as Cinnamomum camphora, Sophora japonica, Koelreuteria paniculata, Privet, etc. The plant landscape is also mainly composed of anti-pollution plants.

Native plants in Pingdingshan
Cinnamomum camphora is the city tree in Pingdingshan. Cinnamomum camphora has been planted in Pingdingshan since the 1990s. It has a long history of cultivation and a large scale of planting area. Cinnamomum camphora is a large evergreen tree and a subtropical evergreen broad-leaved tree. It is evergreen all the year round with luxuriant branches and leaves, and it is an excellent tree species as a shade tree, street tree and sound insulation forest. At the same time, Cinnamomum camphora is an important environmental protection tree species because of its resistance to Cl₂ and other toxic gases.
The regionality of plant image creates regional plant landscape. Due to the different natural conditions, there are rich and diverse native plants in various places. Native tree species are incomparable in adaptability, stress resistance and cost. The native plants in Pingdingshan include Torreya grandis, Elm, Paulownia, Rhamnus, Sapindus, Shan tong zi, Lian xiang, etc. The common evergreen trees are Cinnamomum camphora, Magnolia grandiflora, Arborvitae, Sabina chinensis, Cedar, Pinus tabulaeformis, Osmanthus, Privet etc.; And the common deciduous trees are Purple-leaf plum, Koelreuteria paniculata, Ginkgo, Ailanthus altissima, Chinese tallow, Melia azedarach, Sophora japonica, Albizia, Acer truncatum, Paper mulberry, Paulownia, Cotinus coggygria etc.

Regional plant landscape of Pingdingshan
Through the analysis of the common garden plants in Pingdingshan, the common garden plants in Pingdingshan are shown in Table 2. It can be concluded that in the industrial city, the plants with strong anti-pollution ability are mostly selected. For example, Cinnamomum camphora, Privet, Platanus, Koelreuteria paniculata, Magnolia grandiflora, and Zelkova schneideriana, etc., are mainly used as street trees; In the industrial zone, Sophora japonica, Melia azedarach, Ailanthus altissima, Ash tree, Paper mulberry. These plants either have strong noise reduction, smoke and dust resistance, or have a strong resistance to toxic gases. They have a strong adsorption and purification effect on industrial waste gas, and they can not only beautify the environment, but also purify the air and degrade the heavy metal pollution in the soil. In parks and residential areas, ornamental plants choose Ginkgo, Purple leaf plum, Albizia, Acer monoes, Acer palmatum, Chinese Tallow and Osmanthus, these plants not only have the characteristics of strong adaptability and strong resistance, but also have beautiful tree shape and hue changes; The plants in the waterfronts not only consider the landscape effect, but also consider the purification of water quality. For example, Reed can degrade the biological metabolism; Lotus can also reduce the content of phosphorus and nitrogen in the water, and increase the content of dissolved oxygen in the water.

Conclusion
The regional plant landscape not only has better ecological benefits, but also better demonstrates the city's regional characteristics and human culture. Through the analysis of the plant landscape in Pingdingshan, Henan Province, the plant landscape of industrial cities has more consideration of the ecological benefits of plants, such as the use of plants to purify air and soil to play an environmental role. At the same time, in the plant landscape construction of Pingdingshan, native plants have not been fully used. During the investigation process, the plant landscape with local characteristics is relatively lacking, with relatively few evergreen plants and colourful leaf plants, and the hue change of the plant landscape is slightly monotonous. There are few applications of plants to reflect urban characteristics. When creating a regional plant landscape, it is not only necessary to "fit the place with trees", but also to reflect the regional characteristics with the plant landscape. How to use plants to better show the urban style is a crucial aspect to be considered in the creation of plant landscapes.