Abstract: A laboratory incubation of soil samples was conducted to study the dynamics of three kinds of microbialderived amino sugars in forest soil after adding different amounts of nitrogen. The relative contribution of soil fungi and bacteria to soil nitrogen transformation and accumulation was also investigated by the ratio of glucosamine to muramic acid. The results showed that, dynamics of the soil amino sugar contents were closely related to the nutrient status of the soil. When nitrogen was added to the soil, the microorganisms could use the extraneous nitrogen to synthesize their own cell wall material, and the content of muramic acid in the high nitrogen treatment was higher than that in the low nitrogen treatment, while the content of glucosamine in the high nitrogen treatment was lower than that in the low nitrogen treatment. Our study indicated that increased nitrogen addition was more beneficial to the accumulation of bacteriaderived muramic acid. However, high nitrogen addition was detrimental to the accumulation of fungiderived glucosamine. The response of galactosamine to nitrogen addition was weak. When soil nutrient was deficient, the amino sugars could be decomposed with different degrees. In addition, the ratio of bacteriaderived amino sugar to fungiderived amino sugar was changed. We found that the contribution of bacteria to soil nitrogen transformation in soil was greater than that of fungi, and the contribution of bacteria to soil nitrogen transformation was greater under high nitrogen addition. This study indicated that nitrogen addition changed the microbial transformation of amino sugarderived soil nitrogen.

Key words: grazing, Inner Mongolia typical steppe, litter decomposition, soil animal community