An experiment was conducted to study the distribution and seasonal changes in fine root biomass of Larix gmelinii and Betula platyphylla forests in Great Xing' an Mountains. Results showed that there was a difference in annual average fineroot ( ≤5 mm) biomass between L. gmelinii and B. platyphylla forests, which were 371.64 and 402.87 g · m-2 respectively. Fine root biomass of the L. gmelinii forest showed the maximum value (411.22 g · m-2) in the midpoint between the trunk and the edge of canopy projection, a higher value (364.94 g · m-2 ) in the edge of canopy projection, and the minimum value ( 338.78 g · m-2 ) appeared close to the trunk. Horizontal distribution of fine roots was similar. The above values of B. platyphylla were 445.87,437.32 and 325.45 g · m-2, respectively. The vertical distribution of fine root biomass of the two forests was affected by the differences in soil physical and chemical properties. Fine root biomass in the 010 cm soil layer in the L. gmelinii and B. platyphylla forests accounted for 52.20％ and 57.78％ of the total biomass respectively. Fine root biomass of the two forests showed significant seasonal variations in the growing season. The maximum values of the L. gmelinii (598.80 g · m-2 ) and B. platyphylla forests (528.97 g · m-2 ) appeared in July and September respectively, while the minimum values both appeared in May.%以大兴安岭兴安落叶松(Larix gmelinii)林和白桦(Betula platyphylla)林为研究对象,采用挖掘法获取土壤根系样品,研究两树种细根生物量、分布特征及季节动态.结果表明:兴安落叶松林细根(≤5 mm)生物量全年平均值为371.64g·m-2,白桦林为402.87 g·m-2,存在一定的差异;从水平分布上看,兴安落叶松林在树干和树冠投影边缘的中点处细根生物量最大(411.22g·m-2),其次为树冠投影边缘处(364.94g·m-2),靠近树干处最小(338.78 g·m-2);白桦林与落叶松林的情况相同,即树干和树冠投影边缘的中点处最大,其次为树冠投影边缘处,靠近树干处最小,分别为445.87、437.32、325.45g·m-2;从垂直分布上看,由于不同土壤层的理化性质等的不同,两种林分细根生物量主要分布在0～10cm土层,分别占总生物量的52.20%和57.78%;两种林分细根生物量在生长季内均表现出显著的季节变化的差异性,即最小值均出现在5月份,但兴安落叶松林最大值出现在7月份(598.80g·m-2),白桦林则出现在9月份(528.97 g·m-2).
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