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This experiment was conducted in three sites along a desertification gradient in Horqin Sandy Land,Northern China.Soils unamended and amended with five types of plant residue in a wide range of C:N ratios from 9.9 to 82.2 were incubated for 70 days,during which C and N mineralization were measured.Along the desertification gradient from fixed sand dune to semifixed,and mobile sand dune:cumulative CO2-C produced from the unamended soils was 231.6,193.3 and 61.9 μg/g,respectively,while net inorganic N was 22.9,17.6 and 0.9 mg/kg.Soils amended with residues produced more CO2-C than the unamended soils across all sites.During the first 10 days,C mineralization rate of residue-amended soils decreased with the increase of C:N ratio at each site.However,the mineralization rates were poorly correlated with the C:N ratio in subsequent stage of incubation.Soils of mobile sand dune amended with higher C:N ratio (more than 32) residues produced less CO2-C than that of fixed and semifixed sand dune.NO3--N was the predominant form of inorganic N during the mineralization process in sandy soils.Carbon-to-nitrogen ratio (C:N) can be regarded as a predictor of the speed of N mineralization in sandy soil.The more C.microphylla residue with the lowest C:N ratio (9.9) added in soils,the more net inorganic N released.Our results suggest that C.microphylla residue when added to soil would potentially provide short-term plant available N and improve the soil quality in sandy land.The desertification process postponed the release of inorganic N from plant residues.