Temporal profiling resolves the drivers of microbial nitrogen cycling variability in coastal sediments

Area of Science:

• Environmental microbiology
• Coastal ecology
• Biogeochemical cycling

Background:

• Coastal ecosystems face challenges from variable nutrient inputs.
• Understanding microbial nitrogen cycling is crucial for assessing ecosystem health.
• Sediment microbial communities play a key role in nutrient transformations.

Purpose of the Study:

• To assess the potential of sediment microbial nitrogen-cycling gene abundances (DNA and RNA) to spatially resolve coastal areas impacted by nutrient inputs.
• To investigate the relationship between specific nitrogen-cycling genes and different nutrient sources (organic nitrogen, nitrate).
• To evaluate microbial activity metrics for coastal management.

Main Methods:

• Quantification of key nitrogen-cycling genes (amoA, nirS, nirK, nifH) and their transcripts across three sediment depths over two years.
• Site selection in Port Phillip Bay, Australia, representing varied nutrient inputs and forms.
• Analysis of gene and transcript abundances in relation to sediment depth and nutrient conditions.

Main Results:

• Sediments with organic nitrogen inputs showed high archaeal amoA and nirK-a transcript abundances.
• Proximity to nitrate inputs correlated with high nirS transcript abundances, varying seasonally with nitrate levels.
• Isolated sediments exhibited a depth-specific decrease in transcripts, with bacterial β-amoA linked to ammonium levels.

Conclusions:

• Variability in bacterial β-amoA, archaeal amoA, archaeal nirK-a, and nirS transcripts can enhance monitoring of coastal zones affected by anthropogenic nitrogen.
• Bacterial β-amoA transcripts show potential as a metric for spatiotemporal impact assessment of large nutrient loading events.
• Microbial activity metrics offer improved spatial resolution for coastal management strategies.