Can soil nitrate: ammonium ratios influence plant carbon: nitrogen ratios of the early succession plant? Can plant carbon:nitrogen ratios limit the plant growth in early succession? To address these two questions, we performed a two-factor (soil nitrate: ammonium ratio and plant density) randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate: ammonium ratios, the carbon: nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate: ammonium
ratios and plant density influenced the carbon: nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate: ammonium ratios, with the increase of soil nitrate: ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon: nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate: ammonium ratios affected the carbon: nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon.Thus, soil nitrate: ammonium ratios influenced the carbon: nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate: ammonium ratios can be a limiting factor for the growth of the early succession plant.