Effect of Lead on the Physiological Parameters and Elemental Composition of Pinus sylvestris L. and Picea abies (L.) H. Karst Seedlings

Lead (Pb) pollution poses a long-term threat to forest ecosystems, particularly in mountainous areas affected by atmospheric deposition. This study examined the physiological and biochemical responses of juvenile Pinus sylvestris L. and Picea abies (L.) H. Karst seedlings to low concentrations of lead nitrate during early development. Treatments simulated environmentally relevant Pb exposure and focused on pigment composition, oxidative stress markers, soluble protein and proline levels, and elemental content. Both species exhibited hormetic stimulation of photosynthetic pigments at lower Pb concentrations. In P. sylvestris, this effect declined at the highest dose, whereas P. abies maintained pigment levels, suggesting stronger regulatory control. Pb exposure reduced soluble proteins and induced species-specific alterations in MDA and proline levels. Correlation analysis revealed a well-integrated stress response in P. abies, while P. sylvestris showed a more fragmented pattern. Elemental analysis confirmed Pb accumulation primarily in roots, with higher levels in P. sylvestris. Both species experienced reduced root Mg, K, and Mn, indicating ionic imbalance due to Pb2+ interference. Zn content increased in P. sylvestris but decreased in P. abies, possibly reflecting differences in uptake regulation. These species-specific responses support the hypothesis that P. abies activates more effective defense mechanisms against Pb toxicity, while P. sylvestris exhibits a stronger physiological stress response.