Microbial necromass accelerates humic acid formation by reshaping DOM transformation pathways during composting

Area of Science:

• Environmental Science
• Soil Science
• Microbiology

Background:

• Humic acid (HA) formation is key to organic matter stabilization in composting.
• Precursor availability and reactivity limit HA accumulation.
• Microbial necromass is a potential source of stable organic carbon, but its role in humification is unclear.

Purpose of the Study:

• To investigate the direct impact of microbial necromass on humic acid formation during composting.
• To understand the molecular transformation pathways of dissolved organic matter (DOM) influenced by necromass.

Main Methods:

• Laboratory-scale composting experiments.
• Incorporation of anthropogenically prepared microbial necromass.
• Analysis using Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS).
• Statistical analysis using partial least squares structural equation modeling.

Main Results:

• Necromass addition significantly enhanced compost humification (humification index +23.08%, polymerization degree +44.49%).
• FT-ICR MS revealed intensified DOM transformations (oxidation, decarboxylation, Maillard condensation).
• Necromass led to a higher proportion of oxygenated compounds with increased unsaturation and aromaticity.

Conclusions:

• Microbial necromass accelerates stable humic acid formation in compost.
• Necromass indirectly enhances HA formation by regulating DOM intermediates and condensed aromatic structures.
• This study provides molecular-scale evidence for necromass reshaping DOM reaction pathways in composting.