Population Dynamics And Risk Assessment Of Exotic Species Of Rorippa Amphibia On Lawn

Lawns make up a large part in urban green space in China.The temperature changes in a wide range due to obvious seasonality of the north,and the single turf plant is often poorly managed and looked after in the later stage,which makes it highly susceptible to environmental influence,resulting in turf weeding.The exotic plant,Rorippa amphibia is creeping rooted weed that has invaded the urban lawns of Liaoning Province in recent years.It has formed a large-scale dominant community,which not only causes great damage to the aesthetics of the turf and the community ecosystem,but also brings huge losses to our economy,and there shows a tendency for it to continuously spread to surrounding cities.In order to clarify the influence of Rorippa amphibia on turf and the influence of temperature on seed germination,and to determine its risk of invasion,this study carries out related research on Rorippa amphibia and its community of the swimming pool lawn of Shenyang Agricultural University.Results of the research are as follows:(1)With the invasion of Rorippa amphibia,the increase of the number of species in the community slows down and the species distribution tends to be uniform;the dominant species decrease,the diversity increases,and the community structure becomes more complicated.As Rorippa amphibia has a large niche breadth,the plant in sample plot competes with each other.(2)The number of species that depend on each other for existence is reduced,and the interspecific association among species and the community stability are weakened.Rorippa amphibia destroys community structure of the turf,causing the lawn to develop into weeds.The suitable temperature for germination of Rorippa amphibia is 30-35?,the lowest germination temperature is 10?,and the highest is 40?.The temperature does not have an significant effect on the number of leaves of Rorippa amphibia seedlings(P<0.05),while it has an obvious effect on the length of roots,the number of lateral roots and the number of secondary lateral roots(P<0.05).The root length increases first and then decreases with the increase of temperature.It is the longest at the temperature of 25? and significantly decreases at 30-35?.The number of lateral roots and secondary lateral roots decreases with increasing temperature.Temperature of 15-20? promotes the development of lateral roots of Rorippa amphibia,while the temperature of 25-35? can greatly reduces the number of lateral roots.The temperature has a significant effect on the biomass of Rorippa amphibia.The total dry weight of Rorippa amphibia is the highest at 20?.The root cap ratio is the largest at 15? and the smallest at 30?.It decreases with increasing temperature over all,lower temperature promotes the allocation of more biomass to the roots of Rorippa amphibia.It indicates that Rorippa amphibia seeds were suitable for germination at high temperature,but the roots were suitable for growth at low temperature.(3)The risk assessment value of Rorippa amphibia is 2.25,the risk of invasion reaches the highest level,so the introduction should be prohibited.The corresponding risk monitoring and risk management should be implemented in Liaoning Province.