Dynamics of soil physicochemical properties in shrub and grass communities in Ordos Plateau

Changes in soil physicochemical properties can affect plant community succession. Studies on changes in soil physicochemical properties at different stages of shrub encroachment could help restore degraded grasslands. Based on recorded data about different plant communities in the transition zone from Stipa bungeana to Artemisia ordosica, the physical and chemical properties of soil layers at 0-50 cm at six different stages were analyzed. The results showed that in the 0-50 cm soil layer from the S. bungeana to A. ordosica community: 1) soil texture changed significantly from sandy loam to sandy soil (P<0.05); sand in soil gradually increased from 77.5% in stage Ⅰ to 89.2% in stage Ⅵ, and clay and silt in soil decreased from 0.59% and 21.9% in stage Ⅰ to 0.21% and 10.6% in stage Ⅵ, respectively. Surface soil moisture decreased from 6% in stage Ⅰ to 4% in stage Ⅵ, and soil bulk density increased from 1.58 g·m-3 in stage Ⅰ to 1.77 g·m-3 in stage Ⅵ; 2) soil levels of total nitrogen, total carbon, and total phosphorus decreased generally; levels of total nitrogen, total carbon, and total phosphorus in the 0-5 cm soil layer decreased from 0.08%, 0.77%, and 0.41% in stage Ⅰ to 0.03%, 0.25%, and 0.23% in stage Ⅵ, respectively; soil total potassium content changed considerably; 3) during the process of shrub encroachment, soil fertility, quality, and soil moisture decreased; these changes limited grass growth, and provided favorable conditions for shrub development with deep root systems. Therefore, in vegetation restoration, the quality of the surface soil layer should be improved to recover shrub-encroached grasslands.