Effects of grazing exclusion duration on soil N2O emission flux in the meadow wetland of Napahai, Yunnan, China.

Compared with the control, grazing exclusion significantly increased soil water content, pH, organic matter, total nitrogen, available nitrogen and microbial biomass nitrogen, and reduced bulk density. The soil temperature and inorganic nitrogen (NH4⁺-N, NO3⁻-N) decreased first and then increased with the increase of years. The RRᵢ values of plant biomass, soil water content, pH, organic matter, total nitrogen, available nitrogen and microbial biomass nitrogen all peaked under the 7-year grazing exclusion treatment (increased by 7.5%-352.2%).

Correlation analysis showed that N2O emission flux was significantly positively correlated with aboveground biomass, soil water content, pH, and carbon and nitrogen content, and significantly negatively correlated with soil bulk density and plant diversity. The structural equation model (SEM) explained 89.2% of the total variation of N2O emissions, with aboveground biomass (direct effect: 87.5%), soil water content (76.5%), nitrogen content (83.4%), and pH (48.7%) as the main positive driving factors.

In summary, short-term grazing exclusion significantly increased soil N2O emissions in the Napahai meadow wetland by increasing plant aboveground biomass, improving soil moisture and nitrogen availability, and optimizing soil aeration (reducing bulk density), and this effect continued to increase with the extension of grazing exclusion duration.