Dynamics of Soil Organic Nitrogen and its Functions in Soil Carbon Stabilization Processes

Abstract

Soil organic nitrogen (SON) plays an important role in long-term ecosystem productivity and the global C cycle. But estimation and prediction involved with SON for soil C sequestration are not completely accurate due to insufficient knowledge of the dynamics of SON and its chemical composition. We hypothesized that the dynamics of SON has a correlated relationship with SON thermal properties. This hypothesis was examined through measuring the optimal pyrolysis temperatures of SON in soils and humic and fulvic acids via pyrolysis gas chromatographic atomic emission detection method (GC/AED). It appeared that SON optimal pyrolysis temperature shifted from 500 • C for the surface soil to 400 • C for the 25-38 cm depth soil. The low shift of optimal pyrolysis temperatures with increasing humification was also observed from the independent fulvic and humic acids (from 700 • C to 600 • C), suggesting a relationship of SON thermal property with its dynamic changes. The high thermal stability of SON in combination with the major non-heterocyclic N components coupled with polynuclear C illustrates the contributions of SON to the biological and chemical stabilities of SOM.