Data from: How do functional traits syndromes covary with growth and reproductive performance in a water-stressed population of Fagus sylvatica?

A central issue in plant evolutionary ecology is to understand how several coordinated suites of traits (i.e. traits syndrome) may be jointly selected within a single species. This study aims to describe patterns of variation and co-variation of functional traits in a water-stressed tree population and test their relationships with performance traits. Within a Mediterranean population of Fagus sylvatica experiencing recurrent summer droughts, we investigated the phenotypic variation of leaf unfolding phenology, Leaf Area (LA), Leaf Mass per Area (LMA), Leaf Water Content (LWC), water use efficiency (WUE) estimated by carbon isotopic discrimination (d13C), twig Huber-value (HV: the stem cross-section divided by the leaf area distal to the stem), wood density (WDens), and leaf nitrogen content (Nmass). First, a Principal Component Analysis revealed that two main axes structured the phenotypic variability: the first axis opposed leaf unfolding earliness and LWC to LMA and WUE; the second axis opposed LA to HV. These two axes can be interpreted as the opposition of two strategies (water economy versus water uptake) at two distinct scales (leaf for the first axis and branches for the second axis). Second, we found that LMA, LA, leaf unfolding and LWC responded differently to competition intensity, while WUE, WDens and HV did not correlate with competition. Third, we found that all studied functional traits were related to growth and/or reproductive performance traits and that these relationships were frequently non-linear, showing strong interactions between traits. By highlighting phenotypic clustering of functional traits involved in response to water stress and by evidencing antagonistic selection favouring intermediate trait values as well as trait combinations, our study brought new insights on how natural selection operates on plant functional traits in a stressful environment.

植物进化生态学的核心议题之一，是阐明单个物种种内如何对多组协同性状组（性状综合征，traits syndrome）开展联合选择。本研究旨在描述水分胁迫林木种群中功能性状的变异与协同变异模式，并检验其与表现性状的关联。在遭受周期性夏季干旱的地中海欧洲山毛榉（Fagus sylvatica）种群中，我们调查了以下性状的表型变异：展叶物候、叶面积（Leaf Area, LA）、比叶重（Leaf Mass per Area, LMA）、叶片含水量（Leaf Water Content, LWC）、通过碳同位素判别（δ¹³C）估算的水分利用效率（WUE）、小枝Huber值（HV：茎横截面积与茎远端叶面积的比值）、木材密度（WDens）以及叶氮含量（Nmass）。首先，主成分分析（Principal Component Analysis, PCA）结果显示，表型变异由两大主轴主导：第一主轴将展叶早发性与LWC，与LMA和WUE置于对立两端；第二主轴则将LA与HV形成对立格局。上述两大主轴可被诠释为两种策略在两类不同尺度下的权衡：第一主轴对应叶片尺度下的水分保守策略与水分获取策略的对抗，第二主轴则对应枝条尺度下的此类权衡。其次，我们发现LMA、LA、展叶物候及LWC对竞争强度的响应存在显著差异，而WUE、WDens与HV则与竞争强度无显著关联。其三，本研究发现所有被测功能性状均与生长及/或繁殖表现性状存在关联，且此类关联多呈非线性特征，反映出性状间存在强烈的相互作用。本研究通过揭示参与水分胁迫响应的功能性状的表型聚类现象，并证实拮抗选择倾向于保留中间性状值与性状组合，为自然选择如何在胁迫环境下作用于植物功能性状提供了新的认知视角。