Background Pinus sylvestris var. mongolica is the main tree species for the windbreak and sand fixation forests, soil and water conservation forests and farmland protection forests in arid and semi-arid sandy land of China. P. sylvestris var. mongolica has strong drought resistance and low nutrient demand. Its plantation has played a significant role in windbreak and sand fixation in China's sandy land. Mechanical interpenetration and root exudates of P. sylvestris var. mongolica root system affect the physical and chemical properties of soil. The growth and distribution of roots have important significance for the growth and development of P. sylvestris var. mongolica.

Methods In order to explore the root distribution of P. sylvestris var. mongolica, root soil nutrient distribution and the relationship between them, root system and soil nutrients distribution of different soil layers(0-20 cm, > 20-40 cm, > 40-60 cm, > 60-80 cm and > 80-100 cm), different orientations(east, south, west and north) and horizontal distances(0, 0.5, 1.0, 1.5 and 2.0 m) from the trunk of P. sylvestris var. mongolica of 60 years were studied. Root diameter and number of P. sylvestris var. mongolica, contents of soil water, organic matter, total nitrogen, available nitrogen, total phosphorus, available phosphorus, total potassium, and available potassium were determined.

Results 1) The root number and diameter of P. sylvestris var. mongolica decreased with the increase of soil depth and horizontal distance. The roots showed a phenomenon of aggregation in the surface layer (0-40 cm), accounting for 74.63% of the root numbers in the range of 0-100 cm soil layer. Meanwhile, the roots were mainly distributed in the horizontal direction within the range of 0-0.5 m from the trunk, accounting for 44.78% of the root numbers in the horizontal range of 0-2.0 m. 2) The contents of organic matter, total nitrogen, available nitrogen, total phosphorus and available phosphorus increased with the increase of horizontal distance. The overall nutrients indexes were the highest in range of > 1.0-2.0 m. The contents of total potassium and available potassium in the roots soil of P. sylvestris var. mongolica decreased with the increase of the horizontal distance from the trunk. 3) With the increase of soil depth, the soil nutrients contents showed a decreasing trend. The variation law of nutrients in different orientations was not coincident, and the contents of available nutrients were the highest in the northern position. Correlation analysis showed that the root number and diameter of P. sylvestris var. mongolica were significantly positively correlated with soil total nitrogen content.

Conculsions The roots and soil nutrient distribution of P. sylvestris var. mongolica tende to aggregate in the surface soil vertically and in the soil at the edge of the canopy horizontally, and soil available nutrients contents are the highest in the north orientation of the trunk.