Plant biomass amendment regulates arbuscular mycorrhizal role in organic carbon and nitrogen sequestration in eco-engineered iron ore tailings

Abstract

Arbuscular mycorrhizal (AM) symbiosis plays an important role in organic matter (OM) stabilization and aggregate formation in eco-engineered Fe-ore tailings technosol, but their role may be influenced by the properties of tailings technosol with different plant biomass amendment and water supply, which has not been addressed. The present study investigated if different plant biomass amendments-- Lucerne hay (LH) (low C: N ratio) and Sugarcane mulch (SM) (high C: N ratio) -- could influence the AM roles in organic carbon (OC) and nitrogen (N) sequestration in tailings under well-watered or water deficit conditions. Sorghum spp. Hybrid cv. Silk with or without AM fungal inoculation was grown in tailings amended with plant biomass (either LH or SM) for 20 weeks under glasshouse conditions. The OC and N distribution among aggregates of various sizes (based on physical fractionation) were examined in the tailings technosol with different treatments. To uncover the mechanisms of OC sequestration, the mineral composition, OC forms, and the Fe phases in organo-mineral association were determined by means of X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared analysis (ATR-FTIR), quantitative X-ray diffraction (qXRD), and synchrotron-based Fe K edge X-ray absorption fine structure spectroscopy (Fe K edge XAFS) analysis. AM symbiosis stimulated OC and N sequestration in aggregates formed from the amended tailings, which was regulated by the amendment of plant biomass with different C: N ratios. In LH amended tailings, AM symbiosis enhanced OC sequestration in both particulate OM (POM) and mineral-associated OM (MOM) within macroaggregates. In comparison, AM symbiosis enhanced N sequestration in MOM of both macro- and micro- aggregates in the SM amended tailings. Water deficit generally diminished these AM effects. Furthermore, AM symbiosis enriched carboxyl-rich organics in association with Fe/Si-rich minerals within MOM fraction. These results imply that the AM role in OC and N sequestration in Fe ore tailings is regulated by amendment using plant biomass with different C:N ratio, which should be considered in the eco-engineered pedogenesis for sustainable mine site rehabilitation.