Quercus ilex shows significant among-population variability in functional and growth traits but maintains invariant scaling relations in biomass allocation

Analysis of the intraspecific patterns of variation in ecologically relevant traits is important for knowing the genetic potential of a species to adjust to the expected increase in the severity of drought in the Mediterranean region. In this study, we aim to know to what extent phenotypic variation in functional and structural attributes of three provenances of Quercus ilex L. subsp. ballota (Desf.) Samp. saplings is genetically based. In an experiment conducted in growth chambers, we assessed the effects of two levels of water (well watered and water stressed) and light (20 and 130 μmol m−2 s−1) on gas exchange, chlorophyll fluorescence, and leaf reflectance at different times throughout the experiment. At the end of the experiment, we measured leaf area, stem length and diameter, stomatal density, dry mass, and biomass allocation. Saplings from one of the populations (Sayago) performed better than those from the other two, showing higher photochemical efficiency and chlorophyll content and greater leaf, stem, and root dry mass. Saplings from Sayago also showed higher transpiration rates, stomatal density, and conductance and were less susceptible to photoinhibition than other two. The significant population‐associated variations in functional and structural attributes provided indirect evidence indicating that the holm oak exhibits an important degree of heterogeneity in the genetic constitution of its populations. However, the slopes of the biomass allometric relationships and allocation ratios showed that, irrespective of population, plants followed the same patterns of development in terms of biomass allocation, suggesting that evolutionary pressures may be acting to maintain allometric ratios at specific values