Relationship between root distribution characteristics of Mongolian pine and the soil water content and groundwater table in Horqin Sandy Land, China

KEY MESSAGE: Affected by soil moisture and groundwater table, Mongolian pine roots displayed an hourglass-type distribution characteristic, the high roots density distributed in the shallow and deep layers on sand soil. Mongolian pine (Pinussylvestris var.mongolica) is widely planted in arid and semiarid sandy land and serves as an important wind control and sand fixation species. In order to understand the effects of soil moisture and groundwater table on root distribution characteristics of Mongolian pine, we examined root distribution characteristics and determined the soil moisture and groundwater table under Mongolian pine plantations. The results indicated that the vertical distribution of Mongolian pine roots displayed an hourglass-type characteristic that indicated high density in the shallow (5–35 cm) and deep (85–145 cm) layers, but a low density in the middle layer (35–85 cm). Fine roots, which have a strong relationship with water utilization, displayed typical hourglass-type distribution characteristics. The proportion of fine roots in shallow soil layers (5–35 cm), middle layers (35–85 cm) and deep layers (85–145 cm) was 44.67%, 11.8% and 43.53%, respectively. Corresponding to root distribution characteristic, the shallow (0–40 cm) layer and the deep (90–150 cm) layer have a high soil water content than the middle layer. From May to October, the depth of groundwater table in the Mongolian pine plantation showed an increasing trend, from 185 to 291 cm, and the average groundwater table depth was 251 cm. The average height of capillary fringe above the groundwater table was 75.27 cm. Rainfall and groundwater have effects on the soil water content in a Mongolian pine plantation, and that determines the root distribution characteristics of Mongolian pine. The deep root system of Mongolian pine was effectively supplemented by groundwater, which is a necessary condition to maintain Mongolian pine survival and growth in the western Horqin Sandy Land.