Study On An Invasive Plant Species Redroot Pigweed (Amaranthus Retroflexus) In Taiyuan

The growing frequency and impact of invasive plants worldwide threaten biodiversity,ecological environment,and national economies.Many countries and organizations have focused great attention on the prevention of invasive plants.Redroot pigweed is an annual herbaceous plant which could exist in harsh ecological environment.In China there are two distribution centers,one is northwest-North China-northeast;and the other is southeast-Centre China. Currently this weed has distributed and damaged local communities seriously in many areas of China.Redroot pigweed is also notorious in Taiyuan, adversely affecting to flora in the invaded ecosystem,and makes loss of yield in agriculture.In this thesis,we conducted a survey of the species and their distributions in different weed habitats invaded by redroot pigweed in Taiyuan and constructed a risk analysis system in order to interpret the relationship between its occurrence and the environments,and to elucidate the impact of its invasion on plant diversity.The methods and results as follows:(1) A survey of distribution of Redroot pigweed was conducted with square plot method in different habitats in Taiyuan.The results showed:a) Redroot pigweed exists in habitats of farmlands,waste lands and roadsides.b) the most important factors affecting the occurrence and distribution of Redroot pigweed were the level of niche space,the levels of human distribution and different land utilization,etc. (2) Contiguous quadrats were chosen,and variance/mean ratio method was adopted to examine spatial distribution of Redroot pigweed.The results showed:a) the populations of redroot pigweed surveyed showed cluster distribution,and had a trend to random distribution;b) the surveyed populations of redroot pigweed were found from small patch of 120cm×80cm to large patch of 240cm×400cm.(3) A survey of weeds species and distribution was conducted with the square plot method in different habitats in Taiyuan.The data were analysed using principle component analysis(PCA) and correlation analysis in spss. The results showed:a) we recorded twenty-nine weed species that belonged to fifteen families;b) there were different factors affecting the occurance and distribution of weed species in different habitats;c) species diversity decreased when the importance value of redroot pigweed increased;d) the hazards of redroot pigweed to different habitats from high to low is farmland, roadsides and weastland.(4) Aiming at the status quo of redroot pigweed in Taiyuan,we have constructed a risk assessment system for redroot pigweed by 6 primary indices and 14 secondary indices.The results showed:a) it has caused serious damage in farmland;b) such damage is especially severe in vegetable, soybean and wheat crop land.