Changes in soil properties following shrub encroachment in the semiarid Inner Mongolian grasslands of China

摘要

Shrub encroachment is very common in the semiarid regions of China. However, surprisingly little research has been conducted to evaluate the effects of shrubs on soil properties in these regions compared with other regions in the world. Three sites, one without shrub (state 1), one with 13% shrub coverage (state 2), and the third one with 40% shrub coverage (state 3) in the semiarid Inner Mongolian grasslands were selected to investigate the effects of the shrub Caragana microphylla Lam on soil properties. Soil samples were collected from three sites to evaluate the changes of bulk density (BD), grain size distribution, aggregate stability, soil organic carbon (SOC), total nitrogen (TN), and soil water content (SWC) with the development of shrub encroachment. The results showed that BD and soil sand declined, and silt, aggregate >2 mm and the mean weight diameter (MWD) rose from state 1 to state 3, especially in 20-60 cm depths. With the shrub encroachment, the content of SOC and TN increased, and especially, the increase trends were more obvious in the deeper soil than in the surface soil. SWC increased with the development of shrub encroachment at 20-60 cm depths. Greater and deeper water infiltration existed after heavy rainfall in states 2 and 3, suggesting that macropore flow appeared in shrub encroachment sites. All these results indicated that shrub encroachment improved soil physicochemical properties, particularly in deep soil.