Abstract: At the dry valley along Jingsha River, a highly degraded grass community was selected to determine the effect of N、P fertilization on community dynamics.After one growing season of N and P application, the results showed that the above ground biomass and species density increased except the one with the highest P (20 g& #183;a^-1& #183;m^-2)treatment, and the increases caused by N applications were greater than that of P applications, therefore N was the limiting factors for the restoration of community.After the treatment, the density of Gramineae species increased sharply, but that of tree and shrub species did not increase significantly, so we can conclude that the community has become Gramineae dominant within the short term.Both N and P treatment did not caused significant changes in species type and diversity.Up to the end of treatment, NH4⁺、NO3^- and available P in the soil did not increase with the application of N、P, but the content of N and P in the biomass increased。

Key words: dry valley, N and P fertilization, grass community, Jinsha River, biodiversity