The Impact Of Simulated Nitrogen Deposition And Grazing On Spatial Heterogeneity Of N₂O Flux

N₂O has attracted more attention due to its strong warming effects per unit molecular weight,indirect damaging to the ozone layer and long existing time in the atmosphere.In order to accurately estimate N₂O flux at the plot scale,it is necessary to quantify spatial variation in N₂O flux and identify key factors that regulate the spatial variation in N₂O flux at small scales.Atmospheric nitrogen deposition and grazing have strongly affected the structure and function of ecosystem.The analyzing and understanding of the effects of increased nitrogen deposition and grazing disturbance on the spatial heterogeneity of soil N₂O flux and the design of optimal sampling strategies are the preconditions for accurately estimating their effects on the total soil greenhouse gas flux.We proposed a manipulative experiment with treatments of control,nitrogen addition,grazing and nitrogen addition plus grazing in Songnen meadow steppe,northeastern China.We quantify spatial variability in N₂O flux,plant biomass,soil microclimate and soil properties and identify key factors that regulate the spatial variability in N₂O flux under different treatments.Our objectives are to explore the effects of global change factors and land-use types induced grassland ecosystem composition and structure changes on the spatial variability of N₂O flux and unravel the underlying ecological mechanisms.The research results are as follows:?1?The spatial patterns and rates of N₂O flux remarkably varied across the three measurement campaigns?spring,summer and autumn?.The mean N₂O flux in the summer was significantly higher than in the spring and autumn.The changes in patterns of soil temperature,soil water content and soil NO₃^--N,all of which may have altered the spatial heterogeneity of N₂O flux.?2?There were significant differences in N2O flux between the treatments.The N₂O flux in the grazing plus nitrogen addition was the highest,and it was the lowest in the control and grazing plot.Spatial dependence[C/?Co+C?]of N₂O flux in control,grazing,N addition and NG treatments was 0.822,0.940,0.844 and 0.998,respectively.N₂O flux exhibited strong spatial dependence in all treatments.?3?Soil organic carbon,soil temperature,soil water content,pH,soil bulk density in control treatment exhibited strong spatial dependence,which imply that soil properties of Songnen meadow grassland have a strong spatial heterogeneity.Grazing decreased plant aboveground biomass and soil water content,and increased soil temperature.Spatial dependence of above ground biomass and litter biomass in N addition treatment were larger than other treatments.?4?The spatial variation in N₂O flux under four treatments was controlled by plant factors,soil nutrients,and soil physicochemical properties.The controlling factors for regulating N₂O flux depend on treatments.N₂O flux was mostly controlled by aboveground biomass under control and grazing treatments.Soil water content was the most significant predictor of N₂O flux in the N treatment and grazing plus N addition treatment.Our results enable us reduce errors in the estimates of N₂O flux when scaling up from plot-scale measurements to stand,landscape,and regional scales,to understand the mechanisms underlying N₂O flux,to design an optimal sampling approach and to accurately estimate how N₂O flux at the plot scale may respond to grazing,N addition and their interaction in grassland ecosystems.