Leaf Economics and Local Adaptation: Genetic and Plastic Responses Within Mediterranean Annual Species to Macro- and...

Understanding how plants adjust to changing rainfall and intensified drought is vital, particularly in the Mediterranean region. The Leaf Economics Spectrum (LES) framework distinguishes fast-growing plants with high specific leaf area (SLA) and low leaf dry matter content (LDMC) from resource-conserving plants with opposite traits. In drier environments, plants can be expected to exhibit lower SLA and higher LDMC to minimize water loss and enhance drought resilience. However, it is unclear whether this expectation holds within species among locally adapted populations, and how it is modulated plastically by drought and competition.This study investigated SLA and LDMC in five Mediterranean annual plant species across a macroclimatic rainfall gradient (89-926 mm annual rainfall) and contrasting microclimates: more mesic north- and more arid south exposures. Seeds were collected at 15 sites along this gradient, and plants were grown under controlled greenhouse conditions with three experimental treatments: control, drought, and competition.Contrary to LES expectations, plants from drier macroclimates had mostly evolved higher SLA and lower LDMC, suggesting that drought escape strategies via rapid growth and early reproduction were favored over conservative resource use. Microclimatic variation in leaf traits was smaller than macroclimatic variation, although in two species it showed the same trend, with south-exposure plants displaying lower SLA and/or higher LDMC. Plastic responses to drought consistently reduced SLA and increased LDMC, and vice-versa under competition, thus countering the genetically-based macroclimatic pattern. Interestingly, mesic populations showed stronger plastic shifts to competition.Our results show that evolution favored acquisitive leaves in drier sites, while plasticity modulated leaf traits in the opposite direction under drought stress and competition. These findings illustrate the interplay between evolutionary and plastic responses, underscoring the importance of considering both genetic differentiation and plasticity when assessing annual plant responses to future climate change.