Microbial Community Changes in 26,500-Year-Old Thawing Permafrost

Area of Science:

• Environmental microbiology
• Permafrost science
• Arctic ecology

Background:

• Northern permafrost soils hold over half the global soil carbon.
• Rising temperatures cause permafrost thaw, increasing microbial decomposition and greenhouse gas release.
• Impacts on soil microfauna and microbial communities during abrupt thaw remain poorly understood.

Purpose of the Study:

• To investigate the microbiome of an abrupt permafrost erosion event in Northeast Greenland.
• To identify soil parameters driving microbial taxonomic diversity and abundance changes.
• To understand the role of specific microbial taxa in ancient carbon mineralization.

Main Methods:

• Sequencing of prokaryotic 16S rRNA and fungal ITS2 gene regions from finely scaled depth increments.
• Analysis of soil parameters including pH, carbon content, age, moisture, horizons, and permafrost layers.
• Comparative analysis of microbial communities in eroding permafrost over two consecutive years.

Main Results:

• Microbial alpha diversity decreased with increasing soil depth, age, and pH.
• Soil age, horizons, and permafrost layer were significant drivers of microbial beta diversity.
• Proteobacteria and Firmicutes dominated permafrost, with *Polaromonas* as the most abundant taxon.
• Thawed permafrost showed increased abundance of copiotrophic phyla like Bacteroidia, indicating altered carbon utilization.

Conclusions:

• Abrupt permafrost thaw significantly alters soil microbial community structure and diversity.
• Older, deeper, and more acidic permafrost harbors less diverse but distinct microbial communities.
• Changes in microbial composition, particularly the rise of copiotrophic bacteria, suggest shifts in carbon cycling pathways during erosion.