| With the acceleration of climate warming and urbanization,global extreme rainfall events occur frequently.Urban rainstorm and flood disasters caused by heavy rainfall have become increasingly severe and frequent,causing huge economic losses to the world,and China is no exception.From July 17 to 24,2021,Zhengzhou City,Henan Province was hit by a rare heavy rainstorm in history.The flood disaster caused by rainstorm brought a great test to the urban garden system.Therefore,this study investigated and studied the effects of Zhengzhou 7.20 waterlogging on garden plants in Zhengzhou,and explored the effects of flooding stress on the growth morphology,physiology and biochemistry of garden plants and the response mechanism of plants under stress,in order to provide some basic data and theoretical basis for the protection and restoration of garden plants under flooding stress.In this study,the influence of Zhengzhou 7.20 flood disaster on garden plants in Zhengzhou was investigated and data were collected.Six areas,three parks,two roads and one university park were investigated.The damage grades of the investigated trees,shrubs and grasses were graded and evaluated,and the waterlogging tolerance of different garden plants was analyzed.According to the investigation results,four garden plants,Oxalis corymbosa,Ligustrum japonicum ‘Howardii’,Pittosporum tobira and Miscanthus sinensis,which suffered from different degrees of waterlogging were selected for water stress treatment.Four kinds of plants were tested with different flooding depths,and the treatment time was 5 days,10 days and 15 days.The response characteristics of morphological characteristics,growth indexes(plant height,number of leaves and leaf area)and some physiological and biochemical indexes(chlorophyll content,malondialdehyde content and superoxide dismutase activity)of four plants under different flooding conditions were studied.Finally,according to the results of field investigation and waterlogging resistance test,some suggestions are put forward for the optimization model of plant configuration in Zhengzhou park green space after waterlogging.The main results are as follows:(1)Field investigation of 130 plant species.There are 61 species of trees,40 species of shrubs and 29 species of herbs.There are 30 species of plants,such as Cercis chinensis,Photinia × fraseri,and Muhlenbergia capillaris,which are seriously(Ⅴ)waterlogged in the investigated area.Therefore,in the restoration and construction of park green space after waterlogging,these plants are not suitable for planting in low-lying areas and natural revetment areas along rivers and lakes.There are 51 species of plants with strong waterlogging tolerance(damage grade I and II),such as Cinnamomum camphora,Gardenia jasminoides,Iris tectorum,etc.Because of their strong water resistance,these plants are widely used in parks and roadside green spaces in Zhengzhou City.In the future planning and design,the number of such plants can be appropriately increased in suitable areas.The investigation on the waterlogging tolerance of plants shows that after the flood disaster,many factors will affect the survival rate of plants.Besides the factors such as flooding time,flooded parts and tree age,temperature,soil texture,vegetation types and root distribution also affect the survival rate of garden plants.In the later period,some suggestions were put forward on the restoration and control measures of garden plants after waterlogging and the preventive measures before waterlogging.The investigation on waterlogging tolerance of common trees,shrubs and grasses in Zhengzhou park green space not only helps to provide reference for the selection of waterlogging tolerant trees,but also improves the utilization efficiency of land resources in riverside,lakeside and low-lying areas.(2)The results showed that Miscanthus sinensis and Pittosporum tobira had strong adaptability to flooding stress,followed by Ligustrum japonicum ‘Howardii’,and Oxalis corymbosa was poor.In the process of flooding stress,the external morphological characteristics of the four garden plants changed significantly under the influence of different flooding treatments,such as plant wilting,leaf yellowing,leaf shedding and even whole plant death.The plant height of four garden plants Oxalis corymbosa showed a downward trend,the plant height of Ligustrum japonicum ‘Howardii’,Pittosporum tobira and Miscanthus sinensis showed an upward trend,and the number of leaves and leaf area showed a downward trend.The MDA content in the four plants showed a trend of increasing first and then decreasing with the prolongation of waterlogging stress time,and the SOD activity showed a trend of decreasing first and then increasing.The change trend of chlorophyll content was quite different among the four garden plants.Studies have found that garden plants can actively initiate stress defense mechanisms,mainly by adjusting their own growth and SOD activity to improve resistance to adverse flooding environment.Through the waterlogging tolerance test,the response strategies of garden plants to different water treatments were analyzed,and the self-regulation ability of four plants in different water environments was compared,which had important guiding significance for the restoration and establishment of vegetation under waterlogging stress.(3)According to the results of field investigation and waterlogging resistance test,some suggestions were put forward for the optimization model of plant configuration in Zhengzhou park green space after waterlogging.In the allocation of plants in park green space,we should first consider choosing plants with strong waterlogging tolerance and developed roots,which can meet the short-term waterlogging stress;Secondly,ensure that plants can not only optimize urban air quality,but also improve the aesthetic performance of small urban areas and increase their plant survival rate.In addition,attention should be paid to the development of native plants,and the diversity,growth environment,runoff purification effect and ecological function of plants should also be considered.In this study,the garden plants in Zhengzhou City after 7.20 flood disaster were investigated,and the growth morphology and physiological and biochemical changes of plants under water stress were analyzed.Based on this,some suggestions were put forward for the optimization model of plant configuration in Zhengzhou park green space after flood disaster.This study has important reference value for the restoration of urban gardens affected by floods,ecological reconstruction and reduction of greening construction costs. |
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