Effects of exogenous nitrogen on N2O production processes in wetland soils of different restoration phases in the Yellow River estuary.

Abstract

The effects of exogenous nitrogen on N2O production processes in the soils of un-restoration wetland (R0), restoration wetland since 2007 (R2007) and restoration wetland since 2002 (R2002) of the Yellow River estuary were studied, and the contributions of different processes in N2O production were determined. Results showed that the N2O production of restoration wetland soils (R2002 and R2007) with NO3--N addition was much higher than that with NH4+-N addition, but both NH4+-N and NO3--N additions demonstrated inhibition on the N2O production of soils in R0. Although the effect of NO3--N addition on the total N2O production of topsoil in R2002 was significantly higher than those in R2007, the values in R2002 and R2007 were greatly increased with increasing NO3--N addition. The denitrification and nitrifier denitrification processes in restoration wetland soils (R2002 and R2007) were greatly affected by NO3--N addition, but no significant influence on the non-biological processes of soil in R0 was observed. Although NH4+-N addition did not produce significant effects on the total N2O production of wetland soils, the nitrifier denitrification process in R0 soil, the nitrification process in R2007 soil and the non-biological process in R2002 soil were generally stimulated. In R0 and R2002 soils, the N2O produced by non-biological processes was generally eleva-ted with NH4+-N addition, while with NO3--N addition, the non-biological processes generating N2O in R0, R2002 and R2007 soils were generally inhibited, which was closely correlated with the regulation of soil pH caused by the import of exogenous nitrogen. This study found that the enrichment of NO3--N greatly enhanced the total N2O production of wetland soils and significantly altered the original contribution patterns of biological and non-biological processes to N2O production. Thus, special attention should be paid on the influences of nutrient import (particularly NO3--N enrichment) induced by ecological restoration project on N2O production of wetland soils.