Depth-dependent heterogeneity in topsoil stockpiles influences plant-microbe interactions and revegetation success in arid mine reclamation

Covering mine tailings with uncontaminated soil is a common strategy to mitigate environmental impacts and promote ecosystem recovery during post-mining land reclamation. Topsoil is often stockpiled for future use as a capping layer, but prolonged storage alters its physical, chemical, and microbial properties, often hindering revegetation. This study evaluated soil health parameters within the 28-meter depth profile of a 14-year-old copper mine topsoil stockpile to identify key indicators of revegetation success in semi-arid ecosystem. Using non-invasive root phenotyping in rhizoboxes, filled with soils collected from different depth layers, we monitored plant growth and assessed how biochemical variability in stockpile materials affects germination and early establishment. Machine learning models integrating soil properties, plant responses, and sequenced soil bacterial/archaeal and fungal DNA, identified key indicators influencing plant performance. Results revealed significant heterogeneity in soil quality across depths, with distinct biochemical and microbial profiles shaping vegetation establishment. The upper 10 m exhibited greater potential for supporting growth, with seedling survival reaching 95 %, whereas deeper layers showed drastically reduced survival, sometimes as low as 0 %, due to microbial shifts to anoxic conditions and elevated Fe and Mn toxicity. Fungal communities played a dominant role in germination, while archaea were more influential during later plant establishment. Soil parameter comparisons before and after the experiment indicated recovery processes initiated by plant-soil feedback, including fungal community renewal. These findings highlight the role of stockpile formation in preserving soil health attributes critical for ecological recovery and provide practical insights for optimizing land reclamation in semi-arid ecosystems.