Dryland ecosystem regeneration and plant metal(loid) accumulation strategies 60 years after revegetating a mine tailings pond

The revegetation of anthropogenically degraded sites is challenging in drylands where the combination of harsh substrates and climatic stress creates a restrictive environment. Mine tailings are particularly complex, and the number of successfully revegetated sites has remained small. Our study aimed to investigate one of the few successfully revegetated Cu-Mo tailings ponds in a semi-arid part of the U.S. Southwest to improve our understanding of the drivers and barriers of plant establishment. Integrating in situ vegetation surveys, biochemical analyses of plants and soils, and remote sensing, we assessed vegetation structure, composition, and metal(loid) uptake in various sections of the tailings pond and an adjacent natural area. Based on a hierarchical cluster analysis, we found that plant communities at different successional stages corresponded to specific substrate properties across the site. Depending on the biochemistry and thickness of the surface soil, plants exhibited variable nutrients and metal(loid) accumulation in foliage. We also found that certain soil properties may facilitate the mobility of Cu from tailings layers to the surface. Intriguingly, some of the species (hyper)accumulated Cu, Se, and Re at levels of up to ∼750, ∼80, and ∼90 mg kg^-1 respectively. For these species, we established robust elemental benchmarks through the X-ray fluorescence screening of many herbarium specimens from uncontaminated natural locations and confirmed their affinity for elevated metal(loid) accumulation at a larger scale. Our findings can facilitate species selection for future reclamation research and applications. Upcoming work may leverage the same methodological framework to continue closing the knowledge gap of the factors that determine revegetation success or failure in drylands.