The Research Of Asymmetric Warming Of Soil And Atmosphere For Degraded Grassland

Songnen Plain is in the interior of northeast China, which issurrounded by Daxinganling Mountains, Xiaoxinganling Mountains,Changbai Mountains and Songliao Watershed, and it is an independentplain. The dominant vegetation of Songnen Plain is grassland, and itplays an important role on the development of animal husbandry innortheast China. However, due to the unreasonable utilization, such asover grazing, grassland degradation occurred. We selected12meteorological stations in the Songnen Plain, collected the temperaturedata that in1961-2011, and the temperature trends were analyzed. Studythe atmosphere and soil temperature response to the vegetation coverthrough the field experiments. Meanwhile, analyzing the radiationbalance of grassland under different vegetation cover, research themechanism of air and soil temperature change patterns. The main resultsas follows:Songnen Plain area has a significant warming trend, the soil andatmosphere temperature increased by0.34and0.55℃per decade. Theatmospheric and soil warming of Songnen Plain presents asymmetry, andDTR is gradually reduced. Moreover, the soil temperature increased faster than atmospheric temperature, we think it is another form ofasymmetric warming, can be called aboveground and undergroundwarming or soil-atmospheric asymmetric warming.During the growing season, vegetation cover has a significantinfluence on the atmosphere and soil temperature. Our results indicatethat soil and atmospheric temperature have significant month trends,showing a clear single peak; Meanwhile, with the decline in vegetationcover, soil and air temperature gradually increased. During the growingseason, net radiation, sensible heat flux, latent heat flux and soil heat fluxhas a significant month dynamic characteristics, showing a clear singlepeak. As the rain and heat over the same period, net radiation exchange isdominated by the latent heat flux. In addition, the value of bare latent heatflux is greater than the nomal grassland.With the degraded grassland, vegetation cover decreased, resultingin bare ground, and surface albedo of bare rised, leading to reflected moreenergy; Meanwhile, the soil moisture of bare ground is low, a highproportion of sensible heat flux, resulting in higher atmospherictemperatures. Because the vegetation cover and soil moisture normalgrassland are high, the vegetation transpiration and soil evaporation ismore exuberant, the net radiation exchange is dominated by the latentheat, thus the surface energy rapid loss, and the soil temperature decreased rapidly.