Examining variation in hydraulic and resource acquisition traits along climatic gradients tests our understanding of plant form and function.

A goal of comparative physiology is to understand underlying causes of the tremendous diversity of land plant form and function. The hope is that functional diversity of land plants can be distilled to a few traits that together capture the essence of plant form and function (Díaz et al., 2016), thereby simplifying plant diversity into a tractable number of fundamental ecophysiological ‘strategies’ (or plant functional types). However, there has been disagreement and uncertainty as to (1) which traits should make the shortlist – that is what the key dimensions of trait covariation are, and (2) whether broad‐scale trait patterns and the inferred functional tradeoffs hold at smaller scales relevant to predicting species responses to global change (e.g. whether between species trait patterns hold within individual species). In this issue of New Phytologist, the article by Rosas et al. (pp. 632–646) is a thought‐provoking article that investigates within‐ and among‐species variation in key plant traits along a water availability gradient in two major plant families from a European forest

Data from: Within-species patterns challenge our understanding of the Leaf Economics Spectrum

The utility of plant functional traits for predictive ecology relies on our ability to interpret trait variation across multiple taxonomic and ecological scales. Using extensive datasets of trait variation within species, across species, and across communities, we analyzed whether and at what scales ‘leaf economics spectrum’ (LES) traits show predicted trait-trait covariation. We found that most variation in LES traits is often, but not universally, at high taxonomic levels (between families, between genera in a family). However, we found that trait covariation shows distinct taxonomic scale-dependence, with some trait correlations showing opposite signs within versus across species. LES traits responded independently to environmental gradients within species, with few shared environmental responses across traits or across scales. We conclude that, at small taxonomic scales, plasticity may obscure or reverse the broad evolutionary linkages between leaf traits, meaning that variation in LES traits cannot always be interpreted as differences in resource use strategy