Abstract: As the key factors affecting the inorganic nitrogen sources and eutrophication of downstream aquatic system, the vegetation type and topographical feature in a watershed play an important role in soil nitrogen cycle. In this study, a comparison was made on the soil NO₃^--N and NH₄⁺-N concentrations in Changbai larch plantation, Chinese pine plantation, broad-leaved forest, and maize land in a small watershed, aimed to approach the relations between the vegetation types and the characteristics of soil inorganic nitrogen within the watershed. Our results showed that the soil NO₃^--N and NH₄⁺-N concentrations varied significantly with the vegetation types (P<0.05). From downslope to upslope, the soil NO₃^--N and NH₄⁺-N concentrations decreased significantly from upper layer to lower layer, and the soil NO₃^--N concentration in maize land was the highest (11.86 mg·kg^-1), with a higher risk of nitrogen leaching.

Key words: sandy land, shrub root, xylem anatomical structure, hydraulic trait.