Microbially Driven Organic Carbon Degradation and Nutrient Cycling during Macroalgal Decomposition

Area of Science:

• Marine microbial ecology
• Biogeochemistry
• Coastal ecosystem processes

Background:

• Macroalgal blooms release organic carbon (OC) and nutrients, potentially impacting blue carbon sequestration.
• Marine microorganisms are crucial for OC degradation during macroalgal decay, but mechanisms are not fully understood.

Purpose of the Study:

• To investigate microbial regulation of OC degradation and nutrient cycling during macroalgal decomposition using multiomics.
• To identify key microbial players and metabolic pathways involved in breaking down macroalgal biomass.

Main Methods:

• Integrated multiomics: amplicon sequencing, metagenomics, and metatranscriptomics.
• Analysis of coastal sediments with and without decomposing *Sargassaceae*.
• Measurement of extracellular hydrolase activities and environmental drivers (C/N ratio, DOC, TDN, NO3-).

Main Results:

• Decomposing *Sargassaceae* increased sediment total carbon by over 33% and decreased microbial alpha-diversity.
• Upregulation of OC degradation, carbohydrate metabolism, nitrate reduction, phosphorus, and sulfur metabolism pathways.
• Key OC degraders identified as *Vibrio*, *Pseudoalteromonas*, *Alteromonas*, and *Exiguobacterium_A*, enriched in nitrate and sulfate reduction pathways.
• Environmental factors like C/N ratio and nutrient concentrations shaped microbial metabolism.

Conclusions:

• Microbially driven OC degradation is a pivotal process coupled with nutrient cycling during macroalgal decomposition.
• This study advances mechanistic understanding of microbial carbon processing and biogeochemical linkages in coastal ecosystems.
• Findings highlight the role of specific microbial taxa in macroalgal carbon cycling and nutrient dynamics.