B. pinnatum and E. repens hypervolume calculation

1. Trait intraspecific variability determines community dynamics and species coexistence. In response to competition, plants can display intraspecific variability to enhance its competitive ability or stabilize its niche differences with their competitors. This response is multidimensional because it involves changes along different functional axes and inevitable trade-offs between traits. Here, we transposed the recent concept of the multidimensional trait space to the analysis of intraspecific plant response to competition. We specifically tested the following: (1) in the absence of competitors, the plant multidimensional trait space will be packed towards strategies promoting plant colonisation, and (2) with competitors, the plant multidimensional trait space will be directed towards competition with its size and shaping characteristics dependent on competitor species richness.<br><br>2. We studied trait intraspecific variability of two clonal species, Brachypodium pinnatum (L.) P. Beauv. and Elytrigia repens (L.) Gould, in response to competition. We analysed plant response in the absence of competitors and in competition. Competition treatments included intraspecific and interspecific experimental mixtures with increasing species richness. For each target species and each treatment, we built an hypervolume based on six traits involved in the three-dimensional competition (i.e. ramet and connection traits). We measured these hypervolumes for their size, similarity and the contribution of traits in their shaping.<br><br>3. In the absence of competitors and for both species, we demonstrated a multidimensional trait space packing towards a colonisation strategy. Under competition, the multidimensional trait spaces of the two target species were the widest at the extremes of the richness gradient, i.e., intraspecific and interspecific high richness competition treatments. High intraspecific variability either promoted niche differentiation for individuals of similar species or reflected the large range of competitive responses deployed when plants were faced with many different competitor identities. The multidimensional response process was based on fine adjustments of various traits depending on the surrounding neighbourhood composition and more specifically, on the competitor abundances and functional similarity with the target species.<br><br>4. This study emphasised the multidimensionality of species competitive response, and also underlined the so far neglected importance of competitor species richness for trait intraspecific variability and subsequently community assembly.<br><br>

1. 种内性状变异（intraspecific trait variability）决定群落动态与物种共存。植物在面对竞争时，可通过表现出种内变异来提升自身竞争能力，或是稳定其与竞争者的生态位（niche）差异。这类响应具有多维度特征，因为其涉及不同功能轴上的性状变化，且性状间存在不可避免的权衡关系。本研究将近期提出的多维度性状空间（multidimensional trait space）概念，应用于植物种内竞争响应的分析当中。本研究针对性检验了以下两个假说：(1) 无竞争者存在时，植物的多维度性状空间会向促进植物定植（colonisation）的策略方向聚集；(2) 存在竞争者时，植物的多维度性状空间会朝向竞争相关的方向演化，其空间大小与塑造特征取决于竞争者的物种丰富度。

2. 本研究针对两种克隆植物：*Brachypodium pinnatum* (L.) P. Beauv. 与*Elytrigia repens* (L.) Gould，探究其种内性状变异对竞争的响应。我们设置了无竞争者与有竞争者两种实验处理，其中竞争处理采用物种丰富度梯度递增的种内与种间混合种植模式。针对每个目标物种与每种实验处理，我们基于三维竞争相关的6个性状（即分株（ramet）与连接性状（connection traits））构建了超体积（hypervolume）。我们量化了这些超体积的大小、相似性，以及各性状对其空间塑造的贡献度。

3. 在无竞争者的条件下，两个供试物种的多维度性状空间均呈现出向定植策略方向聚集的特征。在竞争条件下，两个目标物种的多维度性状空间在物种丰富度梯度的两端（即种内竞争与高物种丰富度的种间竞争处理）时达到最大。较高的种内性状变异，既可以促进同物种种群内个体间的生态位分化，也反映了当植物面对多种不同竞争者时，其所具备的广泛竞争响应谱。这种多维度响应过程基于植物根据周围邻体组成（尤其是竞争者的多度及其与目标物种的功能相似性）对各类性状进行的精细调控。

4. 本研究既强调了物种竞争响应的多维度特征，同时也指出了竞争者物种丰富度对种内性状变异乃至群落构建（community assembly）的重要性——这一重要性此前尚未得到足够重视。