The effects of grazing and nitrogen addition on spatial variability of soil respiration (SR) at fine spatial scale are poorly understood. Our objectives are to explore the effects of nitrogen addition and grazing induced grassland ecosystem composition and structure changes on the spatial variability of SR and unravel the underlying ecological mechanisms. We proposed a manipulative experiment with treatments of control (CK), grazing (G), nitrogen addition (N), and grazing plus nitrogen addition (NG) in Songnen meadow steppe, northeastern China. Simultaneous measurements of SR, the aboveground and belowground properties were conducted for 75 sampling points in four 15 × 15 m plots both under drought and wet conditions.
Results/Conclusions
Under drought condition, SR exhibited strong spatial dependence in the CK plot. We found linear change with distance in the G plot. The autocorrelation range for SR was higher in the NG plot (6.21 m) than CK plot (1.61 m). In contrast, under wet condition, the ranges of SR in the G and NG plots were similar to that in the CK plot. The G and NG treatment reduced the degree of spatial dependence of SR both under drought and wet conditions. No spatial structure was detected for SR in the N plot both under drought and wet conditions. Spatial autoregressive models indicated the factors driving spatial variation of SR and their contribution to models were different among the different treatments. The models indicated that the aboveground and belowground properties explained 58-59% of the spatial variation of SR in the CK plot. The strongest controlling factor was aboveground biomass in the G plot under drought condition. SR was controlled by soil temperature, bulk density and litter biomass under wet condition. The soil properties were the most significant predictors of SR in the N plot under drought condition. Nevertheless, no significant correlation of the RS with aboveground and belowground properties was found under wet condition. The spatial variability of SR in the NG plot under drought condition was controlled by the soil moisture, while that was controlled by the soil moisture and root biomass under wet condition. Our results suggest that grazing, nitrogen addition, and their interaction alter the spatial structure of SR and this response depends on soil water conditions. The results are essential for understanding the relationship between aboveground and belowground processes of grassland ecosystems and predicting how soil CO2 efflux of Leymus chinensis meadow steppe response to global change and land-use.