Shrubs increase soil resources heterogeneity along semiarid grass slopes in the Loess Plateau

摘要

The response of soil resources to the introduction of shrubs in semiarid grasslands is essential to the distribution of vegetation and revegetation. To determine how soil resources respond to the introduction of shrubs in semiarid grassland slopes, we investigated in the Loess Plateau of China the spatial patterns of soil organic matter (OM), total and extractable nitrogen (N) and phosphorous (P) in grass slopes with shrubs introduced (SS) and in adjacent native grass slopes without shrub introduction (GS). Three soil types, Loessial, Castanozems and Skeletal, were examined to test the influences of soil type on the effects of shrubs on soil resources. Shrub introduction in grass slopes induced significant increases in soil resources, especially in clay rich soils. The best fit models of spatial structure for soil variables differed with soil types in both GS and SS. A Gaussian model described most of the soil resources in GS, but Spherical and Gaussian models were useful for describing spatial structure in SS. Shrub introduction increased the magnitude of spatial heterogeneity, but reduced the effective range of spatial correlation for most variables (OM, N03 ~, total P and extractable P) along grass slopes. The increase of spatial heterogeneity was greater in sandy soil than in clay rich soil. The relationships among OM, N and P were not influenced by shrub introduction. Taken together, the results of this study indicated that shrubs increased soil resources heterogeneity, and these increases varied with soil types in semiarid grass slopes of the Loess Plateau. These changes might cause degradation of the ecosystem in the area, suggesting that shrubs should be avoided in favor of implementing natural rehabilitation with native grasses for the semiarid grass slopes of the Loess Plateau.