Root adaptive strategies of Pinus koraiensis after introducing to the Daxing'an Mountains and the environmental driving factors.

To reveal root adaptive mechanisms of Pinus koraiensis after being introduced to the Daxing'an Mountains, we used 50-year-old P. koraiensis plantations in the introduction areas (Nanmu and Jiagedaqi) as study objects, with the natural distribution area (Dailing) as the control. We analyzed the regional variation characteristics, resource trade-off strategies, and key environmental driving factors of functional traits of first- to third-order fine roots. The results showed that, compared with the natural distribution area, the third-order root tissue density in the Nanmu decreased significantly by 7.2%, and the specific root area increased significantly by 15.0%. The nitrogen content of first- to third-order roots decreased significantly by 28.6%, 21.3% and 26.4%, respectively. The carbon content of second and third order roots decreased significantly by 4.2% and 4.0%, respectively. The third order root stele diameter decreased significantly by 20.8%; and the cortex thickness of first and third order roots increased significantly by 36.2% and 45.7%, respectively. In the Jiagedaqi, the third-order root diameter and tissue density decreased significantly by 14.8% and 9.0%, respectively; the specific root area increased significantly by 29.4%; the nitrogen content of first- to third-order roots decreased significantly by 32.0%, 27.1% and 28.1%, respectively. The third-order root carbon content decreased significantly by 3.9%. The stele diameter of first- to third-order roots decreased significantly by 30.8%, 33.5% and 22.0%, respectively. The cortex thickness of first and third order roots increased significantly by 39.3% and 27.3%, respectively. There were significant differences between the two introduction areas in certain functional traits. The first- to third-order roots of P. koraiensis exhibited a two-dimensional ecological strategy space, with the resource acquisition-conservation trade-off axis being domi-nant. Roots in the natural distribution area tended toward a resource-conservative strategy, while those in the introduction areas tended toward a resource-acquisitive strategy. The foraging-collaboration axis was secondary, with no difference between the two distribution areas. This differentiation in resource acquisition-conservation trade-off was mainly driven by the dual limitation of soil nutrients and water in the introduction areas, where insufficient resource supply promoted a resource-acquisitive strategy. However, this resource deficiency was mainly manifested in the functional traits of specific root orders rather than the overall root strategy. In conclusion, P. koraiensis could synergistically adjust root functional traits during the introduction process, shifting from a resource-conservative to a resource-acquisitive strategy, thereby adapting to the relatively nutrient- and water-limited environment of the Daxing'an Mountains.