Abstract 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.

中文翻译：

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不同树种丰富度的热带人工林叶内性状变异的驱动因素

摘要 在植物生态学中，群落加权特征均值常被用作生态系统功能的预测因子。最近，物种内性状变异也被证实有助于生态系统功能。我们在这里更进一步评估个体内的性状变异，假设植物中的每一片叶子都单独适应其微环境。使用树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子特征如何沿垂直树冠梯度变化。此外，我们测试了混合林分中的生态位划分是否会导致种内叶子性状变异的减少，以及是否也可以在单个树木的水平上观察到生态位划分。我们专注于描述沿着保守 - 获得性生长谱的生长策略的叶子性状。我们发现特定叶面积 (SLA) 的物种内变异随着邻域物种丰富度的增加而减少。采样高度和当地邻域丰富度都有助于解释物种内叶性状变异，然而，不同物种和性状之间的重要性不同。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（叶片N）、SLA、纤维素和半纤维素含量降低。叶N的变化随着邻域物种丰富度的增加而减小，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。我们的研究结果表明，随着植物群落和个体植物水平上物种丰富度的增加，生态位划分增加。我们的研究结果强调了包括个体特征变异以了解生物多样性-生态系统功能关系的重要性。