Dynamics of Weed Community among Three GrowingSeasons in Alpine Cultivated Grassland

Weed abundance and biomass among three perennial grasses(Elymus nutans,Festuca sinensis,and Festuca ovina) cultivated widely in the east Qinghai-Tibetan plateau were studied.Seven different sowing methods and four density levels were used in the experiment.Field quadrats were tracked and investigated for three years.Results showed 30 kinds of weeds in the cultivated grassland during first growing season.Annual broadleaf weeds,such as Trigonotis peduncularis,Chenopodium album,Elsholtzia patrini,and Lamium amplexicaule had considerable impact on the cultivated grassland.In the second growing season,weed abundance was the lowest(19 kinds) among three years.Perennial weeds,such as Chenopodium album、Artemisia tangutica、and Asiatic plantain had impact on the cultivated grassland.In the third growing season,weed abundance was the highest(40 kinds) among three years and Artemisia tangutica,Plantago asiatica,Geranium wilfordii and Humata tyermanni had significant impact on the cultivated grassland.Both F.sinensis and F.ovina exhibited the poorest persistence in the first establishment year then increased in the following seasons,whereas E.nutans showed the best persistence in the first establishment year then decreased in the following seasons.