1.School of Resources and Environmental Engineering,Anhui University,Jiulong Road ,Hefei;2.School of Resources and Environment, Anhui Agricultural University;3.Anhui University;4.School of Resources and Environment,Anhui Agricultural University, Changjiang West Road
National Natural Science Foundation of China
腐殖质（humic substance, HS）作为农业生产中土壤养分组成的重要指标，在维护土壤地力、碳储存、植物营养及生态环境稳定性等方面具有重大战略意义。然而，由于HS的天然提取源不足，导致HS市场供给需求逐年攀升。鉴于木质素与HS的结构相似，能否采用人工腐殖化方法，精准调控大分子木质素的氧化分解或其小分子衍生物的自由基耦合，生成可媲美甚至超越商业HS作用和功效的类HS产品？该创造性思路对实现我国农业连续增产增收具有极大的经济价值和应用前景。本文简述了天然HS的结构特征和多功能属性，探讨了人工腐殖化的最新理念、方式和机理，对比了人工腐殖化产物与天然HS的差异性，并总结了人工腐殖化产品在农业实践中的潜在应用和价值，旨在为研究者攻克木质素及其衍生物人工腐殖化的科技瓶颈提供理论支撑和技术指导。
Humic substance (HS) is the major component of soil organic matter and chemically can be depicted as a collection of diverse, relatively low-molecular-mass components of organic molecules, forming dynamic associations and stabilized by hydrophobic interactions and hydrogen bonds on the nanometer scale. The physiological effects of HS are widely documented and summarized as a result of enhancing nutrient use efficiency, aiding assimilation of both macro and micronutrients, and stimulating plant growth by induction of carbon, nitrogen, and secondary metabolism. Based on the formation mechanism and multifunctional properties of natural HS, scientists have applied HS to extracellular electron transport, environmental repair, cellular stress, and plant growth promotion. However, due to the limited supply of natural extraction sources of HS such as lignite, weathered coal, and peat, the market supply-demand of HS is increasing year by year. Given that the molecular structures of lignin and its derivatives are similar to natural HS, it is important to ask the question of whether artificial humification methods can be used to accurately control the oxidative decomposition of large-molecular lignin and/or the radical coupling of its small-molecular derivatives to synthesize humic-like products. Another important factor to consider is whether the synthesized products can match and even surpass the effects and functions of commercial HS. This creative idea has great commercial value and application prospects for realizing a continuous increase in agricultural production and income in China. In this review, we briefly generalized the sources, structure characteristics, and functional attributes of natural HS. The latest concept, mode, and mechanism of artificial humification by the use of macromolecule lignin and its derived-small phenolics are discussed, and the differences between artificial humification products and natural HS are also compared. It is confirmed that both artificial humification products and natural HS have C, H, O, N, and S elements, but the content of N in natural HS is higher than that of artificial humification products. In addition, they both contain phenolic ?OH, ?COOH, and aromatic components. Compared with artificial humification products, natural HS has more aromatic structures, but fewer oxygen-containing groups. Moreover, we explored the application values of artificial humification products in agricultural production. The agronomic effects of artificial humification products are extremely significant. On the one hand, artificial humification products can ameliorate soil physicochemical properties, increase soil fertility and water-holding capacity. On the other hand, these humic-like products are also able to serve as plant nutrient pools for promoting crop growth and development, improving nutrient use efficiency and crop yield. Therefore, the practical applications of artificial humification products are of great significance for agricultural production. At present, artificial humification techniques such as chemical oxidation, hydrothermal reaction, bio-composting, Fenton reaction, and fungal laccase-catalyzed oxidation have displayed a great application potential in the precise control of humic-like substance synthesis. In particular, fungal laccase exhibits unique advantages in humic-like substance synthesis due to its dual mechanism of oxidative decomposition and radical coupling. The humification reactions induced by fungal laccase have the characteristics of high catalytic efficiency, simple and controllable operating conditions, low energy requirements, and environmental protection, thus can be used to synthesize a variety of humic-like products. Also, the advantages and disadvantages, process paths, and main control factors of these humic-like substance synthesis technologies are summarized. Hence, this study provides theoretical support and technical guidance for researchers to conquer the artificial humification of lignin and its derivatives and the technology bottleneck of its large-scale application.
Li Shunyao, Qi Xuemin, Chen Meihua, YANG Wei, SUN Kai, LI Yucheng. Promising Applications of Artificial Humification and its Products in Agricultural Production[J]. Acta Pedologica Sinica,,[In Press]