A mutualistic relationship between grasses,coal-degrading fungi,and arbuscular mycorrhizal fungi was proposed to account for the phyto-biodegradation of coal discard.In this study pot trial experiments were carried out to confirm transformation of the carbonaceous substrate,in the presence of a suite of coal degrading fungi and arbuscular mycorrhizal fungi,into a humic-enriched soil-like material in the Cynodon dactylon/coal rhizosphere.The results show that after 47 weeks of C.dactylon growth on coal discard the concentration of humics increased from (62.9 ± 1.5) to (112.1 ± 5.4) mg/kg.Substrate humic acid-like substance concentration positively correlated (r2 =0.95) with accumulation of above ground C.dactylon biomass.FTIR spectroscopy of the extracted hurnic-like substances confirmed both product identity and increased oxidation of the coal discard substrate.Substrate ash content and electrical conductivity declined coincident with an increase in humic acid-like substance concentration,which together reduced the intensity of acidity in the C.dactylon/coal discard rhizosphere.These observations support the proposal that biological oxidative degradation of coal discard leads to increased humic-like substance concentration and formation of a soil-like material.Results have profound implications for use of coal discard as an organic substrate to replace topsoil in phyto-bioremediation strategies for sustainable large-scale rehabilitation of coal discard dumps.
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