中文摘要：

细根在森林生态系统C分配和养分循环过程中发挥着重要作用。细根形态不但影响养分和水分的吸收．而且与细根寿命和周转有密切关系。因此，研究森林树种的细根形态对了解根系结构与功能、预测寿命与周转具有重要理论意义。该文根据细根分枝等级划分方法，研究了东北帽儿山天然次生林20个阔叶树种1～5级根直径、根长和比根长等形态指标。结果表明，20个树种中，除5个树种1级根直径略大于2级和比根长略小于2级根外，其余15个树种均表现为1级根直径和根长最小、比根长最高，随着根序增加，直径和根长增加，而比根长降低。20个阔叶树种前3级根的累积根长均占前5级根总根长的80％以上。9个内生菌根侵染的树种的平均直径、根长和比根长均大于11个外生菌根侵染的树种。

英文摘要：

Aims We studied root morphology across the first five branch orders of 20 hardwood tree species from secondary forest in northeastern China. Our objectives were to determine how root mor- phology changes across root branch orders and how such variations of root morphology differ between ectomycorrhizae （EM）-dominated and arbuscular mycorrhizae （AM）-dominated fine roots. Methods The fine roots were sampled in secondary forest in August 2006. We chose a random location in a plot under a randomly chosen individual tree and used a shovel to remove six soil blocks, 20 cm×20 cm× 10 cm depth, from which the intact root segments were collected and placed in a Whirl-pac bag on ice in a cooler and then transported to the lab and frozen for dissection at a later date. In the laboratory, we dissected each individual root by branching order beginning with the distal end of a root system. After the dissection, we verified the type of mycorrhizal infection by staining and direct micro- scopic observation and determined diameter, length, and specific root length （SRL） of a given order. Important findings Root diameter and length increased, and SRL decreased from the first to fifth order roots, except in Ulmus pumila, Acer ginnala, Alnus sibirica, A. mandshurica and U. laciniata, in which first order roots had larger （or equal） diameter and lower SRL compared to second order roots. The first three order roots accounted for 80% of the total length, suggesting that lower order roots would have similar physiological functions despite their differences in morphology. Eleven species were EM, and nine were AM. Average diameter, length and SRL of each root order were larger for AM than EM species. Key words fine roots, morphology, branch order, hardwood, secondary forest