Leaf trait data for species Fraxinus ornus, Pinus halepensis and Quercus ilex from IDENT Macomer in 2025

Sampling was conducted between 14 and 20 May 2025. The three species Fraxinus ornus, Pinus halepensis, and Quercus ilex were sampled in monocultures as well as in mixtures containing two and four species per plot (three replicates each for the control and irrigation treatments and species diversity level). Within each plot, one individual was selected for sampling. Selected individuals had to be vital and, if possible, located away from the plot edges in order to avoid edge effects. To assess leaf functional traits, leaf samples were collected from branches at different heights and orientations. For F. ornus, three leaves per individual (from different heights and orientations) were sampled. For P. halepensis, three branches per individual (from different heights and orientations) were collected, each comprising at least 30 needles. For Q. ilex, three branches per individual (from different heights and orientations) were sampled, each containing at least 10 leaves. The modified sampling protocol for F. ornus was necessary because individuals of this species in mixed plots often exhibited poor growth and carried only a limited number of leaves. To avoid compromising plant vitality, only three leaves per individual (typically consisting of 5–9 leaflets) were collected. All samples were stored in plastic bags and kept in cooled boxes until further processing in the laboratory. Following field sampling, leaf material was prepared for trait measurements. For F. ornus, one leaf per sampled position was selected; for P. halepensis, seven needles from each of the three sampled branches; and for Q. ilex, two leaves from each of the three sampled branches were selected for scanning to determine leaf area. Subsequently, fresh mass was measured for each sample (F. ornus: three leaves; P. halepensis: 21 needles; Q. ilex: six leaves). Samples were then placed in labeled paper bags and dried at 60°C. Based on these measurements, specific leaf area (SLA) and leaf dry matter content (LDMC) were calculated. For near-infrared spectroscopy (NIRS) analysis, dried leaf samples were ground into a fine powder using a ball mill. The resulting powders were analyzed with a near-infrared spectrometer, and trait values including carbon-to-nitrogen ratio (C:N), nitrogen content, lignin content, and phenolic compounds were predicted from the obtained absorption spectra.