Microbial Nitrogen Transformation Potential in Sediments of Two Contrasting Lakes Is Spatially Structured but...

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Limnology

Background:

• Nitrogen (N) is essential but excessive anthropogenic inputs cause eutrophication.
• Freshwater lake sediments are crucial for N removal through microbial processes.
• Microbial communities driving N transformations in lake sediments are poorly understood.

Purpose of the Study:

• To investigate microbial communities and N removal rates in lake sediments.
• To assess the impact of trophic status on microbial N cycling.
• To link genomic N transformation potential with observed N removal efficiencies.

Main Methods:

• Integrated biogeochemical and microbiological study of eutrophic and oligotrophic lakes.
• Estimation of N removal rates using pore water concentration gradients.
• Metagenomic analysis of microbial N transformation gene abundance (seasonal and spatial).

Main Results:

• Contrasting nutrient levels correlated with distinct microbial communities and N transformation gene abundances.
• Spatial variability in microbial communities and gene abundance was more pronounced than seasonal variability.
• Eutrophic Lake Baldegg exhibited higher denitrification potential (nosZ abundance, nirS:nirK ratio) and N removal efficiency.
• Oligotrophic Lake Sarnen showed higher nitrification potential, with abundant Nitrospira, some capable of comammox.

Conclusions:

• Trophic status significantly influences the composition and functional potential of microbial N-cycling communities in lake sediments.
• Genomic potential for N transformation is key to interpreting N process rates and lacustrine N cycle responses.
• Understanding these microbial dynamics is vital for managing anthropogenic N impacts on aquatic ecosystems.