In plant ecology, community-weighted trait means are often used as predictors for ecosystem functions. More recently, also within-species trait variation has been confirmed to contribute to ecosystem functioning. We here go even further and assess within-individual trait variation, assuming that every leaf in a plant individually adjusts to its micro-environment. Using forest plots varying in tree species richness (Sardinilla experiment, Panama), we analysed how leaf traits within individual trees vary along the vertical crown gradient. Furthermore, we tested whether niche partitioning in mixed stands results in a decrease of within-species leaf trait variation and whether niche partitioning can be also observed at the level of individual trees. We focused on leaf traits that describe the growth strategy along the conservative-acquisitive spectrum of growth. We found a decrease in within-species variation of specific leaf area (SLA) with increasing neighbourhood species richness. Both sampling height and local neighbourhood richness contributed to explaining within-species leaf trait variation, which however, varied in importance among different species and traits. With increasing sampling height, leaf dry matter content (LDMC), carbon to nitrogen ratio and lignin content increased, while leaf nitrogen concentration (leaf N), SLA, cellulose and hemicellulose decreased. Variation in leaf N decreased with increasing neighbourhood species richness, while the magnitude of within-individual variation of most traits was unaffected by neighbourhood species richness. Our results suggest an increased niche partitioning with increasing species richness both in a plant community and at the level of individual plants. Our findings highlight the importance of including within-individual trait variation to understand biodiversity-ecosystem functioning relationships.

在植物生态学中，社区加权特征方法通常被用作生态系统功能的预测指标。最近，物种内性状变异也被证实有助于生态系统的功能。假设植物中的每片叶子都根据其微环境进行了单独调整，我们将在此进行更深入的评估，以评估个体内部的性状变异。使用树木物种丰富度不同的森林地块（Sardinilla实验，巴拿马），我们分析了单个树木内的叶片性状如何沿垂直冠冠梯度变化。此外，我们测试了混合林中的生态位分配是否会导致物种内叶片性状变化的减少，以及是否还可以在单​​个树木的水平上观察到生态位分配。我们专注于叶子特征，这些特征描述了沿着保守性-获取性增长方式的增长策略。我们发现，随着邻近物种丰富度的增加，特定叶面积（SLA）的种内变异减少。采样高度和局部邻里丰富度都有助于解释物种内部的叶片性状变异，但是，不同物种和性状之间的重要性差异很大。随着采样高度的增加，叶片干物质含量（LDMC），碳氮比和木质素含量增加，而叶片氮浓度（叶氮），SLA，纤维素和半纤维素降低。随着邻域物种丰富度的增加，叶片氮素的变化减小，而大多数性状的个体内变异幅度不受邻域物种丰富度的影响。我们的结果表明，在植物群落中和在单个植物的水平上，随着物种丰富度的增加，生态位分配的增加。我们的发现突出了包括个体内性状变异对理解生物多样性-生态系统功能关系的重要性。