The mechanism whereby tree species richness and identity affect the production of fine roots (≤ 2 mm) in forests remains controversial. Complementarity effects (via resource partitioning and facilitation, CEs) and selection effects (that is, dominant of species with particular traits, SEs) are the two hypotheses to explain biodiversity effects on ecosystem functions. This study aimed to (1) examine how tree species diversity affects fine root production and (2) disentangle the complementarity effect and the selection effect on the relationship between biodiversity and fine root production. A total of 60 tree clusters with 15 combinations of diversity gradients consisting of 1–4 tree species (Pinus massoniana, Choerospondias axillaris, Cyclobalanopsis glauca and Lithocarpus glaber) were established in subtropical forests. The sequential soil core and ingrowth core methods were used in each cluster to measure fine root biomass and productivity. Fine root production increased with increase in tree species richness. The biodiversity effects on fine root production mostly resulted from CEs. In the nongrowing season, in most cases, the CE on biomass was positive and became stronger as richness increased, but the opposite situation was observed in the growing season. The strong positive and negative effects of the proportions of C. glauca and L. glaber in the tree clusters on fine root biomass, CEs and SEs, suggest the coordinated action of species diversity and identity in modulating biodiversity effects on belowground processes.

树木丰富度和同一性影响森林细根（≤2 mm）产生的机制仍存在争议。互补效应（通过资源分配和促进，CEs）和选择效应（即具有特定特征的物种的优势，SEs）是解释生物多样性对生态系统功能的两个假设。本研究旨在（1）研究树木物种多样性如何影响优良根系生产；（2）消除互补效应和选择效应对生物多样性与优良根系之间关系的影响。共有60个树丛，具有15种多样性梯度组合，其中包括1-4种树种（马尾松，南酸枣，青冈和Lithocarpus glaber）在亚热带森林中建立。在每个群集中使用顺序土壤核和向内生长核方法来测量细根生物量和生产力。优良的根系产量随着树木物种丰富度的增加而增加。生物多样性对优良根系生产的影响主要来自CE。在非生长季节，在大多数情况下，生物量的CE呈阳性，并随着丰富度的增加而增强，但在生长季节却观察到相反的情况。C. glauca和L. glaber的比例具有强烈的正面和负面影响 在细根生物量，CE和SE上的树丛中，表明物种多样性和同一性在调节生物多样性对地下过程的影响方面的协调作用。