Arbuscular mycorrhizal colonization enhanced organic carbon and nitrogen sequestration in technosols eco-engineered from Fe ore tailings with different plant biomass residues

Eco-engineering Fe ore tailings into technosols (i.e., soil-like growth substrates) has been advocated to be a promising technology for sustainable rehabilitation of tailings with native plant communities ^1-3. Arbuscular mycorrhizal (AM) symbiosis has been found to be able to colonize tailing technosol eco-engineered through exogenous plant biomass input, and contributed to aggregate development and organic matter stabilization in the tailings⁴. However, the AM performance and their eco-functionality usually varies depending on water conditions and tailing technosols developed from different plant biomass residue (PBR) input, which has yet been addressed in previous studies. Therefore, the present study aimed to investigate the role of AM symbiosis in aggregate development and association of organic carbon (C) and nitrogen (N) with mineral phase of aggregates in the developing technosols eco-engineered from Fe ore tailings, in relation to low water supply and plant biomass residues of contrasting nutrient quality (e.g., C:N ratios). The results showed that AM symbiosis did not influence aggregate development, but stimulated organic carbon and nitrogen stabilization  in tailings-technosol. In particular, AM symbiosis enriched organic C (rather than N) sequestration in minerals of tailings-technosol amended with Lucerne hay containing high N and low C:N ratio. Comparatively, AM symbiosis seemed to have enriched significantly N (rather than organic C) in aggregate minerals in tailings-technosols amended with Sugarcane mulch (with low N and high C:N ratio). This increased N sequestration may have resulted from N-rich AM fungal exudates or fungal biomass. AM symbiosis enhanced organic matter sequestration through enhancing associations between carboxyl-rich organics and key Fe-rich phyllosilicates and/or Fe(oxy)hydroxides. Drought stress limited AM symbiosis role in organic C and N sequestration in the tailing-technosol. In summary, the study indicated that plant biomass of different C:N ratio could influence AM role in organic matter stabilization in Fe ore tailings-technosol, and further studies are required to unravel implications of different organic C and N sequestration in aggregate minerals of tailings-technosols, in relation to long-term pedological development and sustainability of soil functions.

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• Li, Z.; Wu, S.; Liu, Y.; Yi, Q.; You, F.; Ma, Y.; Thomsen, L.; Chan, T.-S.; Lu, Y.-R.; Hall, M.; Saha, N.; Huang, Y.; Huang, L., Arbuscular mycorrhizal symbiosis enhances water stable aggregate formation and organic matter stabilization in Fe ore tailings. Geoderma 2022, 406.