Nutrient Stoichiometry Shapes Microbial Community Structure in an Evaporitic Shallow Pond

Area of Science:

• Microbial Ecology
• Limnology
• Nutrient Biogeochemistry

Background:

• Freshwater microbial communities are influenced by nutrient availability and ratios.
• The Cuatro Ciénegas Basin (CCB) in Mexico presents an oligotrophic desert oasis with high microbial diversity.
• Understanding nutrient effects is crucial for managing these unique ecosystems.

Purpose of the Study:

• To investigate the impact of nutrient stoichiometry on microbial community structure in the CCB.
• To test the hypothesis linking phosphorus requirements to bacterial rRNA gene copy number.
• To assess the effects of different nitrogen:phosphorus (N:P) ratios on planktonic and sediment microbial communities.

Main Methods:

• A mesocosm experiment was conducted in Lagunita pond (CCB) with four treatments: control, P-only, N:P=16, and N:P=75.
• Quantitative PCR of the 16S rRNA gene was used to analyze bacterial proliferation.
• Pyrosequencing of 16S and 18S rRNA genes characterized bacterial and microbial eukaryotic communities in water and sediment.

Main Results:

• Phosphorus enrichment alone promoted bacterial taxa with high rRNA gene copy numbers.
• Nutrient enrichment altered planktonic microbial community composition in a treatment-dependent manner.
• Fertilization favored rare bacterial taxa over abundant ones and enriched eukaryotic communities with phototrophs.

Conclusions:

• Nutrient stoichiometry is a key factor shaping microbial community structure in oligotrophic freshwater ecosystems.
• The study provides evidence for the link between phosphorus and bacterial rRNA gene copy number.
• Planktonic and sediment microbial communities respond differently to nutrient enrichment, with sediment communities showing high inherent variability.