The importance of species richness to ecosystem functioning and services is a central tenet of biological conservation. However, most of our theory and mechanistic understanding is based on diversity found aboveground. Our study sought to better understand the relationship between diversity and belowground function by studying root biomass across a plant diversity gradient. We collected soil cores from 91 plots with between 1 and 12 aboveground tree species in three natural secondary forests to measure fine root (≤ 2 mm in diameter) biomass. Molecular methods were used to identify the tree species of fine roots and to estimate fine root biomass for each species. This study tested whether the spatial root partitioning (species differ by belowground territory) and symmetric growth (the capacity to colonize nutrient‐rich hotspots) underpin the relationship between aboveground species richness and fine root biomass. All species preferred to grow in nutrient‐rich areas and symmetric growth could explain the positive relationship between aboveground species richness and fine root biomass. However, symmetric growth only appeared in the nutrient‐rich upper soil layer (0–10 cm). Structural equation modelling indicated that aboveground species richness and stand density significantly affected fine root biomass. Specifically, fine root biomass depended on the interaction between aboveground species richness and stand density, with fine root biomass increasing with species richness at lower stand density, but not at higher stand density. Overall, evidence for spatial (i.e. vertical) root partitioning was inconsistent; assumingly any roots growing into deeper unexplored soil layers were not sufficient contributors to the positive diversity–function relationship. Alternatively, density‐dependent biotic interactions affecting tree recruitment are an important driver affecting productivity in diverse subtropical forests but the usual root distribution patterns in line with the spatial root partitioning hypothesis are unrealistic in contexts where soil nutrients are heterogeneously distributed.

中文翻译：

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正树多样性对细根生物量的积极影响：通过密度依赖性而不是空间根分配

物种丰富度对生态系统功能和服务的重要性是生物保护的中心原则。但是，我们大多数的理论和机理理解都是基于地上的多样性。我们的研究试图通过研究植物多样性梯度上的根生物量来更好地理解多样性与地下功能之间的关系。我们在3个天然次生林中的91个样地中收集了1到12种地上树种的土壤核心，以测量细根（直径≤2 mm）生物量。分子方法被用来识别细根的树种，并估计每个物种的细根生物量。这项研究测试了空间根系分配（物种在地下区域中是否有所不同）和对称生长（在营养丰富的热点地区定殖的能力）是否支撑了地上物种丰富度与优良根生物量之间的关系。所有物种都倾向于在营养丰富的地区生长，并且对称生长可以解释地上物种丰富度与细根生物量之间的正相关关系。但是，对称生长仅出现在营养丰富的上层土壤中（0-10厘米）。结构方程模型表明，地上物种丰富度和林分密度显着影响细根生物量。具体来说，细根生物量取决于地上物种丰富度与林分密度之间的相互作用，在较低林分密度下，细根生物量随物种丰富度而增加，但不是在更高的林分密度下。总体而言，空间（即垂直）根分区的证据不一致。可以肯定的是，任何根系生长到未开发的更深的土壤层中，不足以积极促进多样性与功能的关系。另外，影响树木募集的依赖密度的生物相互作用是影响不同亚热带森林生产力的重要驱动力，但是在土壤养分分布不均的情况下，符合空间根分区假设的通常根分布模式是不现实的。