Trait-based plant ecology a flawed tool in climate studies? The leaf traits of wild olive that pattern with climate are not those routinely measured

Abstract

Climate-related studies have generally focussed upon physiologically well-defined ‘mechanistic’ traits rather than ‘functional’ ones relating indirectly to resource capture. Nevertheless, field responses to climate are likely to typically include both ‘mechanistic’ specialization to climatic extremes and ‘functional’ strategies that optimize resource acquisition during less climatically-severe periods. Here, this hypothesis was tested. Seventeen traits (six ‘functional’, six ‘mechanistic’ and five ‘intermediate’) were measured from 19 populations of oleaster (wild olive) along a climatic gradient in Morocco. Principal components analysis of the trait dataset identified size and the ‘worldwide leaf economics spectrum’ as PCA axes 1 and 2. However, contrary to our prediction, these axes, and commonly-measured ‘functional’ traits, were little correlated with climate. Instead, PCA 3, perhaps relating to water-use and succulence, together stomatal density, specific leaf water content and leaf shape, patterned with altitude, aridity, rainfall and temperature. We concluded that, at least for slow-growing species, such as oleaster, ‘mechanistic’ traits are key to identifying mechanisms of climatic restriction. Meaningful collaboration between ‘mechanistic’ and ‘functional’ disciplines provides the best way of improving our understanding of the global impacts of climate change on species distribution and performance.

Resisting Aridification: Adaptation of Sap Conduction Performance in Moroccan Wild Olive Subspecies Distributed Over an Aridity Gradient

“…The small size and the relative high density of the stomata contribute to the effective control of stomatal transpiration (Connor, 2005). Moreover, a range of leaf traits of Moroccan populations of wild olive (WO) (e.g., dry matter content, surface area, and stomata density) were found by Kassout et al (2019) to be strongly related to ecological parameters associated with aridity. Such traits may be considered as the key elements for understanding physiological tolerance and adaptation to drought of Mediterranean plant species (Kassout et al, 2019).…”

“…Evergreen shrubs dominate such vegetation, usually with small sclerophyllous leaves, as part of their drought tolerance strategy (Lo Gullo and Salleo, 1988). Thus, some Mediterranean genera exhibit a wide range of mechanisms to withstand drought, and this implies that several morphophysiological and biochemical traits are involved in the control of water loss (West et al, 2012;Kassout et al, 2019). Olive (O. europaea L.) is the most iconic sclerophyllous Mediterranean tree.…”

“…In Morocco, from North to South, the wild olive tree is widely distributed in a range of plant communities along a latitudinal gradient of aridity. A recent study demonstrates the existence of functional responses to aridity, which is mainly reflected by a "trade-off " between leaf functional traits (Kassout et al, 2019). In some ways, this ecogeographical gradient of aridity indicates future climate changes and upcoming pressures on tree populations.…”

Image analysis of Moroccan carob seeds (Ceratonia siliqua L.) revealed substantial intraspecific variations depending on climate and geographic origin

“…Principal component analysis (PCA) was performed for inter-population comparisons of trait values, using FactoMiner R package (Lê et al 2008). To quantify the trait variance across the studied hierarchical levels of geographic zones, populations, trees, and seeds, a variance decomposition procedure was used (Albert et al 2010b;Kassout et al 2019). The lme() function in the nlme package (Pinheiro et al 2021) was used to fit a general linear model using the restricted maximum likelihood method (RMEL) across the studied levels, and then the varcomp() function in the ape package (Paradis et al 2004) was used to extract the variance expressed at each level.…”

“…More importantly, the understanding of its seed trait variability according to environmental factors could bring new insights on carob responses to changes in environmental conditions (Saatkamp et al 2019). Thus, it will contribute to the consolidation of trait-based models taking into account the intraspecific variations (Albert et al 2010a, b), which represent a large fraction of the total trait variation (Kassout et al 2019;Kuppler et al 2020).…”