Soils sustainable management: How artificial humic acid reprogram bacterial consortia for enhanced humus synthesis

Long-term farming has led to the loss of soil organic carbon (SOC) pools and humus. However, the process of soil humification takes a relatively long time under natural conditions. The addition of exogenous organic carbon to soil is an economical and efficient strategy for promoting soil carbon sequestration and humification. Hence, our team created a hydrothermal humification technology to generate artificial humic acid (A-HA) from straw. This study explored the differential mechanisms of A-HA in the primary humification process of soybean soil and paddy soil by fluorescence spectroscopy, high-throughput sequencing, and metabolic pathway analysis in a 180-day culture experiment. In soybean soil, A-HA could increase the abundance of Cyanobacteria and Chloroflexi through other carbon fixation pathways and photosynthesis to achieve soil carbon sequestration. Furthermore, D-erythrose-4p produced by the pentose phosphate pathway was used for the formation of humus compounds by carbohydrate metabolism and amino acid metabolism, such as phenylalanine, tyrosine and tryptophan biosynthesis and catecholamine biosynthesis. In paddy soil, A-HA could increase the abundance of Actinobacteriota for converting organic matter into protein-like substances and UVA humus-like substances. Meanwhile, A-HA enhanced butanoate metabolism (related to sugar metabolism), monolignol biosynthesis (related to biosynthesis of polyphenols), and serine biosynthesis (related to amino acid metabolism) for degradation of organic matter and humus formation. This study first proposed that A-HA could regulate microorganisms to effectively accelerate soil humification, while providing mechanistic insights for sustainable soil management. • A-HA increase humic acid content in soybean and paddy soil by 41.60% and 56.88%. • A-HA promote C fixation by Cyanobacteria and Chloroflexi in soybean soil. • A-HA improve Actinobacteriota abundance enhancing soil humification in paddy soil. • A-HA stimulate amino acid metabolism to generate humus precursors in soybean soil. • A-HA regulate polyphenol humification pathway for humus synthesis in paddy soil.