Abstract: With average-tree-specific sampling method,the authors measured the root biomass of Pinus yunnanensis forests with different stand ages in Yongren County,Yunnan Province.The results indicated that total root biomass increased from 8.50 t·hm^-2 in young stand (15～17 yr) to 11.70 t·hm^-2 in middle-aged stand (30～32 yr),and to 18.91 t·hm^-2 in mature stand (60～130 yr).Among different stand age classes,the biomass of coarse roots (>10 mm) varied greatly (1.5～12.3 t·hm^-2),whereas those of medium (5～10 mm) and fine（<5 mm）roots showed less variation (medium roots 1.4～1.6 t·hm^-2, fine roots 5.3～6.2 t·hm^-2).The root biomass of mature stand decreased with soil depth,approximately 93% of total underground biomass being distributed in surface layer (0～30 cm),and only 7% in deeper layer (30～115 cm).

Key words: Mycorrhizas, Morphological diversity, Species diversity, Functions diversity, Plants