关键词: 禁牧年限, N₂O排放, 植物多样性, 土壤性质, 纳帕海, 草甸

Abstract: We examined the changes in soil nitrous oxide (N₂O) emission from meadow communities with different grazing exclusion periods (1, 4, and 7 years) in Napahai Wetland. We measured soil N₂O flux using the static chamber-gas chromatography method, combined with the logarithmic response ratio (RR_i) to investigate its spatiotemporal variations, and analyzed the impact mechanisms of grazing exclusion duration on N₂O emissions. The results showed that grazing exclusion significantly promoted soil N₂O emissions. The RR_i value increased with the extension of grazing exclusion duration, with the RR_ivalue under the 7-year grazing exclusion treatment being 5.6 times that of the 1-year treatment. Compared with the free grazing control, grazing exclusion significantly increased aboveground and underground biomass (increased by 42.8%-611.9%), and decreased the Margalef, Shannon, Pielou, and Simpson indices of plants (decreased by 15.1%-59.3%). Grazing exclusion significantly increased soil water content, pH, organic matter, total nitrogen, available nitrogen, and microbial biomass nitrogen, and reduced soil bulk density. Soil temperature and inorganic nitrogen (NH₄⁺-N, NO₃^--N) decreased first and then increased with the increase of grazing exclusion duration. The RR_i 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%). Soil 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 explained 89.2% of the total variation of N₂O emissions, with aboveground biomass (direct effect: 87.5%), soil water content (76.5%), soil nitrogen content (83.4%), and soil pH (48.7%) as the main positive driving factors. In summary, short-term gra-zing exclusion significantly increased soil N₂O emissions in the Napahai meadow wetland by increasing aboveground biomass, soil moisture, nitrogen availability, and soil aeration (reducing bulk density), and such effect continued to increase with the extension of grazing exclusion duration.

Key words: grazing exclusion duration, N₂O emission, plant diversity, soil property, Napahai, meadow