Abstract: In many terrestrial ecosystems, nitrogen (N) and phosphorus (P) are the most limiting nutrients. In order to determine the nutrient status in semiarid sandy grassland in Keerqin, this paper examined the nutrient dynamics of Artemisia scoparia and Pennisetum flaccidum in their growth period under different fertilizer additions, and based on the principles and methods of N∶P stoichiometry method, investigated the nutrient limit in the grassland. The results showed that the N and P concentrations of A. scoparia and P. flaccidum aboveground biomass had a significant seasonal dynamics under different fertilizer additions. The N concentration of the two species decreased with time, and its dynamics could be simulated by linear model (Y=a+bX) and power function model (Y=aX^b). The coefficient b in the equations could be used to indicate the relative growth rate of the shoot under different nutrientstatus. The relationship of P concentrations of the two species with time could be simulated by quadratic equation (Y=aX²+bX+c). Comparing with the nutrient concentration under different fertilizer additions, N was the main limiting nutrient to most species in semi-arid sandy grassland in Keerqin. N fertilizer addition increased N concentration and N:P ratio of the aboveground biomass. P fertilizer addition had little effects on A. scoparia, but increased the P concentration and N:P ratio of P. flaccidum.

Key words: Species diversity, Species richness, Ecosystem function, Degraded ecosystems