Abstract: A pot experiment was conducted to investigate the effects of nitrogen addition, drought, and different sowing methods on the adaptive characteristics of Stipa krylovii and Allium polyrhizum in the same habitat. We examined the ecological stoichiometry of the aboveground and belowground parts of both species. The results showed that: (1) Nitrogen addition significantly increased the N content of both species, N∶P in the aboveground part of S. krylovii, N∶P and C∶P in the aboveground part of A. polyrhizum; and decreased the P content in the aboveground part of A. polyrhizum, C∶N in the belowground part of S. krylovii and C∶N in the aboveground part of A. polyrhizum. (2) Drought increased N∶P of both species, C∶P of the aboveground part of S. krylovii and C∶P of the belowground part of A. polyrhizum; and decreased P content of S. krylovii and A. polyrhizum and C∶N of the belowground part of A. polyrhizum. (3) Mixed sowing increased C content of the belowground parts of S. krylovii and A. polyrhizum, N content of the aboveground part of A. polyrhizum, the C∶N and C∶P of S. krylovii and C∶N of the belowground part of A. polyrhizum; and decreased N content of the aboveground part of S. krylovii, N content of the belowground part of A. polyrhizum, P content of S. krylovii, P content of the belowground part of A. polyrhizum, C∶N of the aboveground part and N∶P of the belowground part of A. polyrhizum. In summary, N addition reduced aboveground N use efficiency of S. krylovii and A. polyrhizum, and increased aboveground P use efficiency of A. polyrhizum; drought increased P use efficiency in both species and exacerbated P limitation; mixed sowing increased N and P use efficiency of S. krylovii. Under the conditions with increasing nitrogen deposition and drought, the growth of both species will be increasingly limited by P.

Key words: nitrogen deposition, drought stress, sowing method, ecological stoichiometry, nutrient limitation