Abstract: In this paper,an investigation was made on the species composition of turf weeds under three management levels in Hohhot during 2000～2002.The results showed that there were 80 species in total,with 67,37 and 36 species under lower,medium and higher management levels,respectively.Compositae,Legumiosae and Gramine were the dominant families,and the biological spectrum of weed communities were differed with turfs.Based on the index of harm degree,the turf weeds could be classified into five degrees,i.e.,extreme,heavy,medium,light and weak.Under lower,medium and higher management levels,the extremely and heavily harm turf weed species occupied 11.95%,21.63% and 22.22%,respectively.The extremely harm weed species included Viola prionantha,Digitaria ischaemum and Leymus secalinus,Viola prionantha and Geranium sibiricum,Potentilla anserine,L.secalinus and Inula britanica,respectively in the three management levels.V.prionantha,L.secalinus were the dominant species in spring and autumn,and D.ischaemum in summer.G.sibiricum was the dominant species in whole season.

Key words: Arabidopsis thaliana, Carbon dioxide, Response