Humic substances readily identifiable in the environment are involved in several biotic and abiotic reactions affecting carbon turnover, soil fertility, plant nutrition and stimulation, xenobiotic transformation and microbial respiration. Inspired by natural roles of humic substances, several applications of these substances, including crop stimulants, redox mediators, anti-oxidants, human medicines, environmental remediation and fish feeding, have been developed. The annual market for humic substances has grown rapidly for these reasons and due to eco-conscious features, but there is a limited supply of natural coal-related resources such as lignite and leonardite from which humic substances are extracted in bulk. The structural similarity between humic substances and lignin suggests that lignocellulosic refinery resulting in lignin residues as a by-product could be a potential candidate for a bulk source of humic-like substances, but structural differences between the two polymeric materials indicate that additional transformation procedures allowing lignin architecture to fully mimic commercial humic substances are required. In this review, we introduce the emerging concept of artificial humification of lignin-related materials as a promising strategy for lignin valorization. First, the core structural features of humic substances and the relationship between these features and the physicochemical properties, natural functions and versatile applications of the substances are described. In particular, the mechanism by which humic substances stimulate the growth of plants and hence can improve crop productivity is highlighted. Second, top-down and bottom-up transformation pathways for scalable humification of small lignin-derived phenols, technical lignins and lignin-containing plant residues are described in detail. Finally, future directions are suggested for research and development of artificial lignin humification to achieve alternative ways of producing customized analogues of humic substances.

在环境中易于识别的腐殖质物质参与了几种生物和非生物反应，这些反应影响碳的转化，土壤肥力，植物营养和刺激，异源生物转化和微生物呼吸。受腐殖质自然作用的启发，已经开发了这些物质的几种应用，包括作物刺激剂，氧化还原介体，抗氧化剂，人类药物，环境修复和鱼类摄食。由于这些原因和具有生态意识的特征，腐殖质的年度市场增长迅速，但是与天然煤有关的资源（如褐煤和变绿石）的供应有限，大量从腐殖质中提取腐殖质。腐殖质和木质素之间的结构相似性表明，木质素纤维素精炼厂产生的木质素残留物可能是大量腐殖质类物质的潜在候选者，但是两种聚合材料之间的结构差异表明，额外的转化程序可以需要木质素结构以完全模仿商业腐殖质。在这篇综述中，我们介绍了木质素相关材料人工增湿的新兴概念，将其作为木质素增值的一种有前途的策略。首先，描述了腐殖质的核心结构特征以及这些特征与这些物质的理化性质，自然功能和通用用途之间的关系。特别是，强调了腐殖质刺激植物生长从而提高作物生产力的机制。其次，详细描述了自上而下和自下而上的转化路径，用于小规模木质素衍生的酚，工业木质素和含木质素的植物残基的可规模化腐殖化。最后，为人工木质素腐殖化的研究和开发提出了未来的方向，以实现生产定制的腐殖质类似物的替代方法。