Substrate as architect: lignocellulose structures directed assembly lines for humic acid stability in composting

Area of Science:

• Environmental Science
• Soil Science
• Biochemistry

Background:

• Humic acids (HA) are crucial soil organic matter components.
• Understanding HA formation pathways is key for soil health and carbon sequestration.
• Lignocellulose, a major plant biomass component, serves as a precursor for HA.

Purpose of the Study:

• To investigate how different lignocellulose sources (pine branches, rice straw, willow branches) influence humic acid assembly during composting.
• To elucidate the distinct humification mechanisms driven by varied lignocellulose structures and microbial communities.
• To develop a quantitative metric for assessing aromatic condensation in humic acids.

Main Methods:

• Integrated multi-omics, multispectral analysis, and enzyme activity assays.
• Microbial co-occurrence network modeling to analyze microbial community dynamics.
• Development and application of the Aromatic Condensation Index (ACI) to quantify HA structure.

Main Results:

• Pine branches yielded HA with high aromatic condensation (ACI=0.82) via synergistic biotic and abiotic pathways.
• Rice straw showed rapid humification but low aromatization (ACI=0.51) due to microbial community decoupling.
• Willow branches exhibited delayed, low-aromatization HA formation (ACI=0.38) influenced by recalcitrant lignin and fragmented microbial networks.

Conclusions:

• Lignocellulose source fundamentally dictates humic acid assembly pathways and structural characteristics.
• Microbial community structure and function play critical roles in mediating humification processes.
• This study provides a framework for understanding lignin degradation and offers strategies for its efficient conversion into valuable humic substances.