Pinus sylvestris var. mongolica mediates interspecific belowground chemical interactions through root exudates

• The root exudates of P. sylvestris were abundant in allelochemicals. • P. sylvestris significantly affected the root growth and behaviors of neighbor plants. • A. fruticosa was only positively affected by root contact with P. sylvestris. • Relatively low concentrations of root exudates of P. sylvestris promoted A. fruticosa performance. Managed plantations are normally characterized by monocultures, which lead to ecological problems such as reduced plant productivity and declining ecological services. Considering the potential degradation of Pinus sylvestris var mongolica ( P. sylvestris ) plantations in the Mu Us sandy land, there is still a knowledge gap regarding the selection of suitable sand-adapted species for mixed planting with P. sylvestris to enhance plantation productivity. To this end, we constructed a mixed planting system of two species, including P. sylvestris and six other adaptive species, in the Mu Us sandy land. Through the identification of potential allelochemicals in the root exudates of P. sylvestris and a series of greenhouse experiments, we clarified the effects of the root systems and exudates of P. sylvestris on the performance of adaptive species. The results showed that a total of 1062 root exudates of P. sylvestris were detected, including abundant potential allelochemicals such as fatty acids, phenolic acids, terpenes, flavonoids, and coumarins. Rhizobox experiments showed that the above- and belowground biomasses of Amorpha fruticosa Linn ( A. fruticosa ) and P. sylvestris were significantly and positively influenced by the presence of each other. Through different levels of belowground segregation, only A. fruticosa was positively affected by root contact with P. sylvestris , while the other plants were not affected or inhibited. In addition, relatively low concentrations of root exudates of P. sylvestris promoted A. fruticosa performance. Overall, A. fruticosa was positively affected by the root system of P. sylvestris and its exudates, and it promoted the growth of P. sylvestris ; therefore, it is suitable for mixed-species planting to increase the productivity of monoculture P. sylvestris plantations. Our research provides a potential solution to the problem of the declining productivity of sandy plantations caused by monocultures.