以福建省建瓯市万木林自然保护区6个优势树种为研究对象,使用Li-6400便携式光合测定仪离体测定6个树种1-5级细根呼吸速率。单因素和双因素方差分析表明:树种、序级及其交互作用对6种树种细根比根呼吸均有极显著影响 (<em>P</em><0.01);6种树种细根比根呼吸均随序级的升高呈极显著下降(<em>P</em><0.01),这种变化可分别用二次函数,三次函数,指数函数或幂函数来拟合。相关性分析表明比根长和氮浓度可以很好地表征同一树种不同序级细根的比根呼吸,但两者不能有效表征不同树种同一序级的比根呼吸。协方差分析表明:细根比根呼吸与比根长的相关性在不同树种间具有显著差异,但在不同序级间则表现一致;细根比根呼吸与氮浓度的相关性则在不同树种和序级间均表现不一致。结果表明细根内部存在明显的功能异质性,而比根长可反映特定树种细根的这种功能异质性。;It is increasingly recognized that tree fine roots (<2mm in diameter) are not composed of homogenous units as traditionally assumed. Instead, they include groups of individuals that differ markedly both in structure and function. Fine root respiration is a significant component of carbon cycling in forest ecosystems, however, it is commonly measured according to arbitrary diameter class. To date, few studies have focused on fine root respiration and its relationship with fine root morphology and nutrients across of different root orders, because of the numerous difficulties associated with its measurements,especially in subtropical evergreen broad-leaf forest. So in this study, intact fine root segments of six dominant tree species (<em>Cinnamomum micranthum</em>;<em> Tsoongiodendron odorum Chun</em>; <em>Cinnamomum chekiangense</em>;<em> Castanopsis fabri</em>;<em> Altingia gracilipes</em>; and <em>Castanopsis carlesii</em>) in an evergreen broadleaved forest located at the Wanmulin Nature Reserve, Jian'ou, Fujian province, were collected by excavation, separated into different root orders, and then measured for respiration rate by an Li-6400 portable photosynthesis system. We here aimed to examine the following three questions: (1) the relationship between specific root respiration (<em>SRR</em>) and root order; (2) the effect of root order and tree species on <em>SRR</em>; and (3) the relationship of <em>SRR</em> with specific root length (<em>SRL</em>) and tissue N concentration. The one-way and two-way ANOVA revealed that: tree species, root order and tree species × root order all had significant effects on <em>SRR</em> (<em>P</em><0.01 for all cases). <em>SRR</em> ranged from 0.625 to 1.79 μgC·g<sup>-1</sup>·s<sup>-1</sup> for the lowest root order, and significantly declined with increasing root order, which was consistent for the six tree species(<em>P</em><0.01). This decline, however, differed among species, with <em>SRR</em> decreased most sharply for <em>Cinnamomum chekiangense</em>. The regression analysis showed that <em>SRR</em> changed systematically with root order, which could be represented by quadratic, cubic, exponential or power functions. Across all the root orders, <em>SRR</em> was positively correlated both with <em>SRL</em> and nitrogen concentration for each tree species (<em>P</em><0.01). Across all the six species, <em>SRR</em> was positively correlated (<em>P</em><0.01) with <em>SRL</em> only in the third order, and there was no correlation between <em>SRR</em> and nitrogen concentration in all the five root orders. When pooled by all the tree species and root orders, <em>SRR</em> was positively correlated both with <em>SRL</em> and nitrogen concentration (<em>P</em><0.01). These means that both <em>SRL</em> and nitrogen concentration could only reflect the intra-species but not the inter-species variations of <em>SRR</em>. The analysis of covariance demonstrated that: tree species had significant effected on (<em>P</em><0.01)the slope of the regression straight line which between <em>SRR</em> and <em>SRL</em>, but root order had no significant effected on slope and intercept of the regression straight line, these means the correlation between <em>SRR</em> and <em>SRL</em> was significantly affected by tree species but not by root orders, and the correlation between <em>SRR</em> and nitrogen concentration was significantly affected both by tree species and root orders. It is concluded that there existed evident functional heterogeneity among fine roots of different branch orders, and <em>SRL</em> could reflect this heterogeneity only in specific tree species.