[Population characteristics of Caragana microphylla and the influencing soil factors in shrub-encroached grassland of Inner Mongolia, China].

We studied the population characteristics of Caragana microphylla and related soil factors across diffe-rent stages of shrub encroachment ( i.e ., light, moderate, and severe) on the Xilingol Grassland of Inner Mongolia. The results showed that the density and height of C. microphylla gradually increased during the process of grassland shrub-encroachment from light to moderate to severe. The density and height were increased by 196.0% and 34.5% from light to moderate stage of shrub encroachment, and were increased by 25.4% and 17.6% from moderate to severe stage. Crown size, basal diameter, tiller number per clump, and aboveground productivity of C. microphylla tented to decrease first and then increase, while the proportion of aboveground biomass allocation to leaves decreased across the stages of shrub encroachment. The competition between C. microphylla and herbaceous species was strongest in the moderate encroachment stage. C. microphylla reduced its lateral growth (such as crown size, basal diameter, and tiller number per clump) and increased density and height to get competitive advantage. Limi-ting soil factors for C. microphylla varied significantly at different stages of shrub encroachment. In the light encroachment stage, soil factors had little effect on the growth of C. microphylla . In the moderate encroachment stage, soil moisture in the deep layer (20-50 cm) and soil pH were the key factors limiting shrub density. In the severe encroachment stage, soil moisture in the deep layer and pH limited the vertical growth of C. microphylla , while soil moisture of shallow layer (0-20 cm) and nutrients were the limiting factors for the lateral expansion of shrubs.