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.