Artificially regulated humification in creating humic-like biostimulators

Humic substances (HSs), as the “black gold” of global agriculture, have a crucial environmental significance in cleaning harmful compounds, maintaining carbon mass balance, and increasing crop productivity. Unfortunately, the resources of HSs extracted from nature are insufficient, causing the supply, demand, and budget of the humus market to gradually increase. Given the analogous architectures of lignin and HSs, artificially regulated humification (ARH) has a great potential for directionally controlling the oxidative cleavage of lignin and/or the radical copolymerization of lignin precursors, to produce reassembled oligomers and/or polymers that can compare favorably with the function and efficacy of HSs. Herein, different ARH strategies are innovatively proposed to tackle hazardous chemicals and create humic-like biostimulators (H-LBs). We briefly describe the characteristics and functionalities of natural HSs, and summarize the latest approaches and mechanisms of lignin and its precursor-based ARH. In particular, the ARH routes of bio-composting, laccase catalysis, white-rot fungal degradation, Fenton-based advanced oxidation, and hydrothermal humification are comparatively highlighted to govern harmful substrates, enhance carbon sequestration, generate H-LBs, and practice sustainable agriculture. Furthermore, the mechanisms for promoting crop growth of H-LBs are also illustrated. Advances in modulating humification pathways may solve the technological bottlenecks of ARH in-situ and ex-situ by well-stocked lignin and its small derivatives, which are important for decontaminating contaminants, reducing CO2 emissions, and enriching H-LBs in agroecosystems.