Arbuscular mycorrhizal symbiosis enhances water stable aggregate formation and organic matter stabilization in Fe ore tailings

Abstract

Organo-mineral association and water-stable aggregation in finely textured tailings are critically important to the eco-engineered soil formation from alkaline Fe ore tailings for sustainable mine site rehabilitation. Arbuscular mycorrhizal (AM) symbiosis plays important roles in soil aggregate formation and organic matter (OM) stabilization. However, it is unknown if AM symbiosis could enhance aggregate formation and OM stabilization in alkaline Fe ore tailings. The present study aimed to investigate the establishment of AM symbiosis and their role in tailing aggregate formation coupled with OM stabilization, as well as the underlying mechanisms. After initial eco-engineering (OM amendment and pioneer plant cultivation) to improve physicochemical conditions for plant survival, Sorghum spp. Hybrid cv. Silk inoculated with/without AM fungi (Glomus spp.) were cultivated in the tailings under glasshouse conditions for 14 weeks. The results indicated that AM fungi formed symbiotic association with Sorghum spp. plants, improved mineral nutrient (e.g., P) acquisition and root growth in the eco-engineered tailings. The AM symbiosis significantly improved aggregate formation. The association of organic carbon and nitrogen with tailing minerals of the aggregates was enhanced by the AM symbiosis. As revealed by synchrotron-based C 1 s near edge X-ray absorption fine structure (C 1 s NEXAFS) and Fe K edge X-ray absorption fine structure (Fe K edge XAFS) spectroscopy, the AM symbiosis favoured carboxyl and aromatic C association with secondary Fe-Si minerals, which may have been formed from AM driven mineral weathering. Overall, the study revealed that the AM symbiosis could not only improve the growth of pioneer plant species in the early eco-engineered tailings, but also advance soil formation through enhancing organic C and N sequestration and physical structure development via water-stable aggregation. These findings help to advance our understanding of the importance of AM symbiosis in the eco-engineering of tailings into functional soil (or technosols) for sustainable rehabilitation of Fe-ore tailings.