Dissolved organic matter defines microbial communities during initial soil formation after deglaciation

Area of Science:

• Soil Science
• Microbial Ecology
• Biogeochemistry

Background:

• Ecosystem succession and soil development (pedogenesis) alter dissolved organic matter (DOM) composition and microbial interactions.
• These changes are particularly dynamic during early soil formation, such as in recently deglaciated regions.
• The impact of DOM on microbial community structure over time and soil depth is not well understood.

Purpose of the Study:

• To investigate the molecular characteristics of water-extractable DOM.
• To link DOM molecular diversity to soil microbial community structure.
• To understand DOM-microbe interactions during initial soil pedogenesis along a deglaciation chronosequence.

Main Methods:

• Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) for DOM molecular characterization.
• High-throughput sequencing for microbial community analysis.
• Molecular ecological network analysis to explore DOM-microbe relationships.

Main Results:

• Dissolved organic matter (DOM) shifted from low- to mid- and high-molecular-weight compounds with increasing soil age and depth.
• Indicators like double bond equivalents and O/C ratios increased, while H/C ratios decreased, signifying DOM accumulation and stabilization.
• Microbial communities shifted towards oligotrophic bacteria (Acidobacteria) and fungi (Mortierellomycota), correlating with more stable DOM components.
• Network analysis revealed reduced DOM-bacterial positive interactions and increased DOM-fungal negative interactions, indicating specialized decomposition pathways.

Conclusions:

• Dissolved organic matter (DOM) stability is context-dependent during early soil formation.
• Bacteria preferentially degrade labile DOM, leaving more stable compounds.
• Fungi play a crucial role in the slower decomposition of these recalcitrant DOM pools, shaping microbial community succession.