Contrasting physiological-biochemical responses and elemental homeostasis in Pinus sylvestris families exposed to As, Cd and Pb.

Contamination with As, Cd and Pb can limit tree establishment on degraded substrates, but family-level variation in Scots pine responses remains poorly resolved. This study evaluated three open-pollinated maternal half-sib families of Pinus sylvestris L. under controlled hydroponic exposure to As, Cd and Pb. Growth, photosynthetic pigments, soluble sugars, phenolic and flavonoid contents, malondialdehyde, antioxidant enzyme activities, elemental composition and metal(loid) accumulation indices were analysed, with PCA and Random Forest used as exploratory integrative tools. Significant family and treatment interactions were observed for all measured physiological and biochemical traits, indicating non-uniform responses among families. Cd produced the clearest toxicity profile, characterized by strong chlorophyll (up to -56.0%) and carotenoid (up to -52.6%) losses, increased lipid peroxidation (up to +70.9%) and marked Fe, Mn and Zn disruption. Pb was retained predominantly in roots (up to 12.96 ± 0.45 g/kg DW), with very low translocation to shoots, but high Pb exposure strongly inhibited root elongation (up to -70.5%). As caused comparatively moderate pigment effects but was associated with increased S (up to +147.4%) and changes in secondary-metabolite and antioxidant traits. No family showed consistently superior performance across all metal(loid)s, although response strategies differed. These results identify integrated physiological and elemental screening of Scots pine reproductive material for phytostabilization-oriented restoration as potentially relevant, while field validation under realistic contaminated-substrate conditions before practical application remains necessary.