Spatial Heterogeneity of Soil Nutrients and Respiration in the Desertified Grasslands of Inner Mongolia,China

There is a limited knowledge of spatial heterogeneity in soil nutrients and soil respiration in the semi-arid and arid grasslands of China.This study investigated the spatial differences in soil nutrients and soil respiration among three desertified grasslands and within two shrub-dominated communities on the Ordos Plateau of Inner Mongolia,China in 2006.Both soil organic carbon(SOC) and total nitrogen(TN) were significantly different(P < 0.01) among the three desertified grasslands along a degradation gradient.Within the two shrub-dominated communities,the SOC and TN contents decreased with increasing distance from the main stems of the shrub,and this "fertile island" effect was most pronounced in the surface soil.The total soil respirations during the growing season were 131.26,95.95,and 118.66 g C m-2,respectively,for the steppe,shrub,and shrub-perennial grass communities.The coefficient of variability of soil respiration was the highest in the shrub community and lowest in the steppe community.CO2 effluxes from the soil under the canopy of shrub were significantly higher than those from the soil covered with biological crusts and the bare soil in the interplant spaces in the shrub community.However,soil respiration beneath the shrubs was not different from that of the soil in the inter-shrub of the shrub-perennial grass community.This is probably due to the smaller shrub size.In the two shrub-dominated communities,spatial variability in soil respiration was found to depend on soil water content and C:N ratio.

There is a limited knowledge of spatial heterogeneity in soil nutrients and soil respiration in the semi-arid and arid grasslands of China. This study investigated the spatial differences in soil nutrients and soil respiration among three desertified grasslands and within two shrub-dominated communities on the Ordos Plateau of Inner Mongolia, China in 2006. Both soil organic carbon （SOC） and total nitrogen （TN） were significantly different （P 〈 0.01） among the three desertified grasslands along a degradation gradient. Within the two shrub-dominated communities, the SOC and TN contents decreased with increasing distance from the main stems of the shrub, and this ＂fertile island＂ effect was most pronounced in the surface soil. The total soil respirations during the growing season were 131.26, 95.95, and 118.66 g C m^-2, respectively, for the steppe, shrub, and shrub-perennial grass communities. The coefficient of variability of soil respiration was the highest in the shrub community and lowest in the steppe community. CO2 effiuxes from the soil under the canopy of shrub were significantly higher than those from the soil covered with biological crusts and the bare soil in the interplant spaces in the shrub community. However, soil respiration beneath the shrubs was not different from that of the soil in the inter-shrub of the shrub-perennial grass community. This is probably due to the smaller shrub size. In the two shrub-dominated communities, spatial variability in soil respiration was found to depend on soil water content and C：N ratio.