Abstract: Taking 3-, 5-, 6-, and 7-year-old triploid Populus tomentosa pulp forests as test objects, this paper studied the monthly dynamics and vertical distribution of their fine root biomass, root length density, and fine root surface area during the growth period April-November 2008. In the growth period, the dynamics of the fine root biomass, root length density, and fine root surface area all presented a unimodal curve, with the maximum of fine root biomass observed in August, and the maximum of root length density and fine root surface area observed in September. The mean values of the fine root biomass, root length density, and fine root surface area all increased with tree age, being 658.3, 750.6, 1048.1 and 1115.0 kg·hm^-2, 12.490×10³, 9.983×10³, 9.227×10³ and 5.921×10³ m·m^-3, and 12.17, 18.68, 22.23 and 25.28 m²·m^-3 for the 3-, 5-, 6-, and 7 years old stands, respectively. Surface soil had the greatest distribution of fine root biomass, root length density, and fine root surface area, and the fine roots in surface soil increased with tree age. 46.36%-51.12% of fine root biomass, 62.77%-75.33% of root length density, and 61.74%-64.16% of fine root surface area were found in 0-10 cm soil layer.

Key words: Lichen biomass, Stocking rate, Plant community, Soil properties