Abstract Plants can express considerable plasticity in leaf functional traits, but that plasticity may be constrained by coordination and trade‐offs among multiple functions. The leaf economics spectrum (LES) describes a well‐supported trade‐off between durability versus productivity but does not capture all dimensions of leaf functional responses to environmental variation. We hypothesized that traits related to photoprotection, desiccation tolerance, and water‐use efficiency (WUE) would occupy axes distinct from, and potentially orthogonal to, the LES, and that species would differ in how they resolve multifunctional trade‐offs along environmental gradients, influencing the strength of within‐ versus between‐species trait relationships. We tested these hypotheses by analysing 11 leaf traits on 219 individuals of 16 woody species in a 20.2‐ha temperate woodland plot spanning a topography‐driven desiccation gradient in the North American Great Plains. Using multivariate ordinations, environmental vector fitting, and complementary bivariate correlation and standardized major axis analyses, we quantified axes of trait coordination and compared relationships within and between species. More productive leaves were less desiccation tolerant, durable, and water‐use efficient, invested less in carotenoid‐related photoprotection, and occurred in more mesic topographic positions. Ordinations revealed novel functional relationships and trade‐offs: WUE was coordinated with carotenoid‐related photoprotection, with more water‐use efficient leaves investing more in photoprotection and less in chlorophylls relative to carotenoids, while desiccation tolerance aligned with durability and traded off with productivity traits. Within‐species analyses confirmed strong, consistent relationships among LES traits and desiccation tolerance, whereas relationships involving WUE and photoprotection—reflecting more dynamic physiological processes—varied among species, producing weak between‐species correlations. Together, these patterns indicate that WUE and photoprotection are coordinated along an axis approximately orthogonal to the LES, capturing covariation among dynamic physiological rather than structural functions. Supporting the idea that how individuals resolve functional trade‐offs along environmental gradients shapes between‐species trait relationships, our study not only expands the leaf economics framework but also reconceptualizes it in relation to critical trade‐offs involving carotenoid‐related photoprotection, desiccation tolerance, and WUE. By identifying new dimensions of trait relationships, our study advances functional ecology by highlighting leaf phenotypic variation along gradients as an integrated expression of multiple interacting functions. Read the free Plain Language Summary for this article on the Journal blog.
McNichol et al. (Thu,) studied this question.