Weak coordination between leaf drought tolerance and proxy traits in herbaceous plants

Abstract

Abstract Increased drought is predicted to have a major impact on plant performance under environmental change. Yet leaf hydraulic traits directly related to drought tolerance, such as leaf turgor loss point ( π tlp ), are under‐represented in trait‐based studies and have been largely overlooked within the main frameworks evaluating trait–trait coordination and trade‐offs—the leaf economics spectrum (LES) and the global spectrum of plant form and function. Using 122 herbaceous species from the Central European temperate grasslands, we investigated (a) the coordination between π tlp and traits often used as proxies for drought tolerance, namely SLA, leaf area (LA), leaf dry matter content (LDMC), leaf thickness (LT), plant height and intrinsic water use efficiency (iWUE); (b) whether the strength of the trait–trait relationships differed across plant functional types (PFTs: graminoids and forbs) and depended on species phylogeny; and (c) whether single or multiple traits, combined with either PFTs or phylogenetic relatedness, provide a good prediction of π tlp . A more negative π tlp (higher leaf drought tolerance) was coordinated with higher LDMC and higher iWUE. This pattern was consistent among PFTs and also after accounting for phylogenetic relatedness. However, the coordination of π tlp with other traits was weak. For LT and height, it was driven by the differences between PFTs. For SLA and LA, it was only observed after accounting for phylogenetic relatedness. The most parsimonious model predicting π tlp as a function of other traits retained LDMC and LA (adj. R 2 = 0.37). Since π tlp showed a strong phylogenetic signal, accounting for the influence of phylogenetic relatedness further improved π tlp prediction by 17%. In herbaceous temperate plants, there is relatively weak coordination between leaf drought tolerance ( π tlp ) and traits representing key dimensions of the LES and the global spectrum of plant form and function. None of the proxy traits considered here, alone or in combination, provided a strong prediction of π tlp across a large number of grassland plant species. Therefore, our work emphasizes the need for direct measurements of leaf hydraulics when estimating plant drought responses to better understand and predict species responses to environmental change. A free Plain Language Summary can be found within the Supporting Information of this article.