Nitrogen Deposition Levels Affect Soil Aggregate Stabilization and Organic Carbon Dynamics by Altering Chemical Composition and Glomalin‐Related Soil Protein in the Desert Steppe of Northwest China

ABSTRACT Anthropogenic nitrogen (N) deposition significantly alters soil aggregate (SA) stability and soil organic carbon (SOC) dynamics in grassland ecosystems, though the effects of varying N deposition levels remain inadequately understood. Here we evaluate the effect of varying N addition levels on SA and organic carbon stability. A 6‐year N addition experiment was conducted in a desert steppe, comprising CK (0 g·m −2 ·yr. −1 ), low N (5 and 10 g·m −2 ·yr. −1 ), medium N (20 g·m −2 ·yr. −1 ), and high N (40 g·m −2 ·yr. −1 ) treatments. This research examined SA stability, GRSP, SOC dynamics, and carbon flow pathways using Fourier transform infrared and 13 C stable isotope analysis. Medium N addition enhanced macro‐SA content (> 0.25 mm) by 20.5% and improved SA stability through increased SOC accumulation, while high N addition decreased macro‐SA content by 7.47%. SOC concentrations in micro‐SA (0.25–0.053 mm) and silt + clay (SC) (< 0.053 mm) increased substantially under low and medium N inputs. Polysaccharide‐C levels were elevated in macro‐SA, whereas phenolics‐C and aliphatic‐C predominated in micro‐SA. Low N addition increased aliphatic‐C in SA, while medium and high N levels reduced it. N addition elevated phenolics‐C and aromatic‐C, particularly in macro‐SA. Both easy extractable GRSP (EE‐GRSP) ( r = 0.71*) and T‐GRSP ( r = 0.59*) correlated positively with SOC, emphasizing GRSP's importance in SOC accumulation. N addition enhanced carbon flow among SA through microbial decomposition and anabolic processes, with plant‐derived carbon preferentially accumulating in macro‐SA and SC. Medium N input optimally promotes SA stability and SOC in desert steppes, providing important insights for understanding N deposition's role in climate change mitigation.