Planctomycetes in lakes: poor or strong competitors for phosphorus?

Area of Science:

• * Aquatic microbiology
• * Microbial ecology
• * Limnology

Background:

• * Perialpine lakes exhibit high nitrogen-to-phosphorus ratios, indicating phosphorus limitation.
• * Planctomycetes are a distinct bacterial phylum with poorly understood nutrient acquisition strategies.
• * Previous assumptions suggest bacteria generally outcompete phytoplankton for phosphorus.

Purpose of the Study:

• * To investigate the impact of nitrogen and phosphorus amendments on Planctomycetes and other bacteria (bacteria-wP).
• * To test if nutrient additions similarly affect Planctomycetes and bacteria-wP community structures.
• * To evaluate Planctomycetes' competitive ability for phosphorus in aquatic ecosystems.

Main Methods:

• * Water samples from two perialpine lakes with different eutrophication levels were used.
• * Inorganic nutrients (nitrogen and phosphorus) were added to assess their effects.
• * Bacterial community structure and composition were analyzed using molecular techniques.

Main Results:

• * Phosphorus addition stimulated phytoplankton growth and altered bacteria-wP community structure.
• * Contrary to expectations, phosphorus addition did not significantly impact Planctomycetes community structure.
• * Nitrogen addition had no significant effect on either bacteria-wP or Planctomycetes communities.
• * Planctomycetes exhibited a long generation time (123 h).

Conclusions:

• * Planctomycetes may be poor competitors for phosphorus, potentially explaining their low abundance in aquatic systems.
• * The study challenges the general assumption of bacterial superiority over phytoplankton in phosphorus competition.
• * Further research is needed to elucidate the complex relationship between Planctomycetes and phosphorus dynamics.