Abstract
Humans are dependent upon soil which supplies food, fuel, chemicals, medicine, sequesters pollutants, purifies and conveys water, and supports the built environment. In short, we need soil, but it has little or no need of us. Agriculture, mining, urbanization and other human activities result in temporary land-use and once complete, used and degraded land should be rehabilitated and restored to minimize loss of soil carbon. It is generally accepted that the most effective strategy is phyto-remediation. Typically, phytoremediation involves re-invigoration of soil fertility, physicochemical properties, and its microbiome to facilitate establishment of appropriate climax cover vegetation. A myco-phytoremediation technology called Fungcoal was developed in South Africa to achieve these outcomes for land disturbed by coal mining. Here we outline the contemporary and expanded rationale that underpins Fungcoal, which relies on in situ bio-conversion of carbonaceous waste coal or discard, in order to explore the probable origin of humic substances (HS) and soil organic matter (SOM). To achieve this, microbial processing of low-grade coal and discard, including bio-liquefaction and bio-conversion, is examined in some detail. The significance, origin, structure, and mode of action of coal-derived humics are recounted to emphasize the dynamic equilibrium, that is, humification and the derivation of soil organic matter (SOM). The contribution of plant exudate, extracellular vesicles (EV), extra polymeric substances (EPS), and other small molecules as components of the dynamic equilibrium that sustains SOM is highlighted. Arbuscular mycorrhizal fungi (AMF), saprophytic ectomycorrhizal fungi (EMF), and plant growth promoting rhizobacteria (PGPR) are considered essential microbial biocatalysts that provide mutualistic support to sustain plant growth following soil reclamation and restoration. Finally, we posit that de novo synthesis of SOM is by specialized microbial consortia (or ‘humifiers’) which use molecular components from the root metabolome; and, that combinations of functional biocatalyst act to re-establish and maintain the soil dynamic. It is concluded that a bio-scaffold is necessary for functional phytoremediation including maintenance of the SOM dynamic and overall biogeochemistry of organic carbon in the global ecosystem
Highlights
Land-use for primary activities such as human settlement, industry and mining often times competes with and threatens regional food security and natural water sources as it consumes arable soil which is far better purposed for agriculture
A recently developed strategy (i.e., Fungcoal), used to rehabilitate open cast spoil, re-vegetate mining disturbed land, and coal discard dumps, was elaborated in detail in an effort to establish the physicochemical characteristics of humic substances (HS), how HS and soil organic matter (SOM) might arise, and the contribution of in situ humification to soil fertility
The accumulated information seems to support ideas that soil microorganisms are capable of either solubilizing or degrading coal discard and coal by-product to render a HS-rich soil-like residue that potentially serves as substrate for microbial humifiers and supra-molecular aggregation of HS into SOM via ‘humification-like’ processes
Summary
Land-use for primary activities such as human settlement, industry and mining often times competes with and threatens regional food security and natural water sources as it consumes arable soil which is far better purposed for agriculture. While every instance is unique, the conventional method (at least in South Africa) has been the import and layering of topsoil to both re-create landform and cloak or mask subsoils and backfill to ameliorate negative impacts of carbonaceous material on the broader environment, and to support and promote the establishment of cover vegetation To this end, disturbed land post-mining is covered in a layer of topsoil (usually 50–100 cm), treated with lime to mitigate acid-generating potential of the substrate, appropriate fertilizers are applied, and the area is re-vegetated using selected annual and perennial species [21,22]. It is concluded that holistic phytoremediation is potentially more favourable, both financially and environmentally, for the sustained stabilization and restoration of disturbed land
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
