Abstract: Ligularia virgaurea is a noxious weed widely distributed in the alpine grassland of east Qinghai-Tibet Plateau of China.This paper studied the allelopathy of its aqueous extract on the pasture plants Festuca sinensis,Bromus magnus,Elymus nutans,Poa annua,and F. ovina in the region.The mean response index (RI) values of the pasture plants were calculated,and used to quantitatively assess the allelopathic sensitivity of the receptors at three levels,i.e.,growth items,development stages,and species.Corresponding values of the weed were also treated in similar way to assess the allelopathic potential of the donor.The results showed that the allelopathic sensitivity was in the order of P.annua>B.magnus>F.sinensis>F.ovina>E.nutans.Both the seed germination and the seedling growth of test pasture plants were inhibited at species level,suggesting that rain eluviation was one of the means by which the weed released allelochemicals.The aqueous extracts from L.virgaurea root and leaf had a significant inhibitory effect at species level,and the effect of root extract was stronger than that of leaf extract,suggesting the competition among species on the underground resources in natural grassland.Allelopathy played an important role in L.virgaurea invasion,and might be responsible to the formation of mono-dominant community and the degeneration of grassland.

Key words: Leaf decomposition, Tilia amurensis, Broad-leaved Korean pine forest