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To address how the ratios of nitrogen and phosphorus(N:P ratios)in soil affect plant growth,we performed a two-factor(soil available N:P ratios and plant density)randomized block pot experiment to examine the relationships between soil N:P ratios,and the N:P ratios and growth rate of Artemisia ordosica seedlings.Under moderate water stress and adequate nutrient status,both soil N:P and plant density influenced the N:P ratios and growth rates of A.ordosica.With the increase of soil N:P ratios,the growth rates of A.ordosica seedlings decreased significantly.With the increase of soil N:P ratios,N:P ratios in A.ordosica seedlings increased significantly.While the nitrogen concentrations in the plant increased slightly,the phosphorus concentrations significantly decreased.With the increase of plant density,the shoot N:P ratios and growth rates significantly decreased,which resulted from soil N:P ratios.Thus,soil N:P ratios influenced the N:P ratios in A.ordosica seedlings,and hence,influenced its growth.Our results suggest that,under adequate nutrient environment,soil N:P ratios can be a limiting factor for plant growth.