Abstract: Pinus densiflora has been introduced to the southern Horqin Sandy Land, China for 50 years. However, little is known about its growth performance, especially for root biomass distribution and architecture characteristics. The growth characteristics of P. densiflora were compared with the same aged P. sylvestris var.mongolica(40 years old). The biomass distribution of different diameter sizes of roots was sampled by the method of layered and full excavation. Meanwhile, root length, root link number as well as average link length were measured, and fractal dimension and fractal abundance were calculated. Growth and biomass of P. densiflorawere greater than those of P. sylvestris var. mongolica. The root biomass of P. densiflora was 1.96 times as much as that of P. sylvestris var.mongolica, and the fine root (≤0.2 cm in diameter) biomass of the former was 4.76 times as much as that of the latter. Root biomass occupied 29.0% of the total biomass for P. densiflora. Its fine root biomass represented only 1.1% of total root biomass, but fine root length accounted for 44.3% of  total root length. Root biomass occupied 25.6% of the total biomass forP. sylvestris var. mongolica. Its fine root biomass represented 0.4% of total root biomass, but fine root length accounted for only 28.8% of its total root length. In terms of root vertical distribution, fine roots of P. densiflora were distributed in the range of 0-180 cm soil, and fine root biomass in the range of 40-180 cm represented 65.2% of total fine root biomass. Almost all the fine roots (99.2%) of P. sylvestris var.mongolica were distributed in the range of 0-100 cm. Fine root biomass in 0-40 cm soil layer accounted for 63.4% of the total. Although there was no significant difference in root average link length between the two species, the link number of fine roots and parts of middle roots (0.2-2.0 cm) for P. densiflora were significantly higher than that forP. sylvestrisvar. mongolica. The fractal dimension of root system for P. densiflora was 1.548±0.251, which was 1.2 times as much as that of P. sylvestris var.mongolica (1.293±0.190). Furthermore, its fractal abundance was 1.3 times as high as of P. sylvestris var.mongolica. Compared with P. sylvestris var.mongolica, root system of P. densiflora has more branches, more complex topology, and stronger absorption ability, which help it make use of deeper soil water and nutrient.

Key words: defoliation, Pinus koraiensis, nitrogen, female cone, phosphorus, nonstructural carbohydrate, girdling