Genetically based trait coordination and phenotypic plasticity of growth, gas exchange, allometry, and hydraulics...

Studying intraspecific trait variation across environments is key for understanding how resource-use strategies evolve. It is hypothesized that plants from mesic environments have evolved toward a more acquisitive strategy with high growth potential and phenotypic plasticity, while populations from xeric continental climates exhibit a conservative strategy with slower growth and better physiological performance under drier conditions. We tested this hypothesis through the phenotypical characterization of 14-yr-old Pinus pinaster Aiton trees from 20 range-wide populations growing in two climatically contrasting common gardens. We measured 20 traits related to growth, leaf morphology, gas exchange, photochemistry, and hydraulics. Consistent with our hypothesis, we found that populations from mesic oceanic areas exhibited higher growth rates and higher allocation to leaf surface area under mesic conditions, along with greater plasticity in these traits. By contrast, xeric continental populations had better physiological status, showing higher gas exchange rates and photochemical efficiency, but lower sapwood-specific hydraulic conductivity under drier conditions. Together, our results provide evidence that climate drives the joint evolution of leaf and stem traits and their plasticity following an acquisitive-conservative axis of resource use. Overall, trait coordination is found to be highly plastic, likely to maximize plant performance under contrasting environmental conditions.