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Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizer used combined with low carbon inputs. The present study investigated the promotion of soil nitrate transformation to soil organic N by different carbon amendments. A laboratory incubation experiment using 15N tracer (K15NO3) was employed to elucidate the proportion of soil organic N derived from accumulated soil nitrate following amendment with glucose (G) or maize straw (S) at controlled soil temperature and moisture content. During the 56-d incubation period we determined the dynamics and isotopic abundance of mineral N (NO3- and NH4+) and soil organic N and greenhouse gas (N2O and CO2) emissions. Carbon amendment markedly stimulated transformation of nitrate to soil organic N. Mineralization of native soil organic N was also enhanced because soil organic N at the end of the incubation period was not significantly different from that in the control without added C. Glucose had a greater effect on nitrate-N immobilization (25.0 mg kg-1) than maize straw (9.4 mg kg-1) and glucose addition also led to highest greenhouse gas emissions. With glucose and straw amendment total N2O-N emissions were 1.01 and 0.03 mg kg-1, respectively. Similarly, glucose amendment lowered the concentration and abundance of NO3--N and increased that of NH4+-N more than maize straw. In agricultural practice straw amendment may be an effective strategy to deplete the excess NO3--N pool and restrict leaching, to promote nitrate-N immobilization and to decrease greenhouse gas emissions.