Varietal-specific growth performance and ecological restoration Potential of Olea europaea L. in Abandoned Mine Slags

Mine ecological restoration is an important means of improving the ecological environment of abandoned mining areas, and the selection and configuration of plant species play a critical role in the restoration outcomes. This study aims to investigate the effects of different types of mining slag on the growth performance and survival rate of olive cultivars, providing a scientific basis for mine ecological restoration. The experimental results indicate significant differences in the physicochemical properties of the mining soils: clay slag had a near-neutral pH (6.856) and an organic matter content of 13.848 g/kg. In comparison, the sandy soil was acidic (pH 5.678) with a slightly higher organic matter content (16.481 g/kg). However, the heavy metal content (e.g., mercury, arsenic, chromium, cadmium, and lead) in sandy soil was generally higher than in clay, which may negatively affect plant growth and ecological restoration. The growth performance of different olive cultivars varied markedly, with ‘Arbequina’ showing the best performance in terms of seedling height (108.67 cm), total growth (58.67 cm), and crown width (92 cm east-west, 85 cm north-south), making it suitable as a primary restoration species for high-erosion-risk areas. ‘Arbosana’ exhibited moderate performance but had a higher survival rate in clay slag (83.75 %), making it suitable for clay-rich areas, while ‘Koroneiki’ showed weaker growth performance. Additionally, the slag type significantly influenced the survival rate of the cultivars: ‘Arbequina’ had the highest survival rate in gravelly slag (92.86 %), ‘Arbosana’ performed better in clay slag (83.75 %), and ‘Koroneiki’ had similar survival rates in both slag types (82.11 % in gravelly slag and 80.95 % in clay slag). Heavy metal accumulation in leaves varied among cultivars, with ‘Arbosana’ and ‘Koroneiki’ accumulating more lead, mercury, arsenic, and cadmium in clay slag, whereas ‘Arbequina’ showed a higher accumulation of all heavy metals in gravelly slag. In conclusion, ‘Arbequina’ and ‘Arbosana’ demonstrated excellent performance in mine restoration and are suitable as primary restoration species, while ‘Koroneiki’ can serve as a supplementary cultivar. By optimizing zonal planting strategies and enhancing management measures, the effectiveness of mine ecological restoration can be significantly improved, offering a feasible solution for vegetation recovery in similar mining areas.