Biological dinitrogen fixation (acetylene reduction) associated with Florida mangroves.

Area of Science:

• Marine Biology
• Environmental Science
• Microbiology

Background:

• Mangrove ecosystems are vital coastal habitats.
• Nitrogen is often a limiting nutrient in marine environments.
• Biological dinitrogen fixation plays a crucial role in nitrogen cycling.

Purpose of the Study:

• To investigate biological dinitrogen fixation rates in Tampa Bay mangrove communities.
• To identify factors limiting or enhancing nitrogenase activity.
• To determine the role of mangrove roots and associated bacteria in dinitrogen fixation.

Main Methods:

• Acetylene reduction technique was used to measure nitrogenase activity.
• Experiments were conducted on plant-free and plant-associated sediments.
• In situ measurements and amendments with carbon sources were performed.
• Nitrogenase activity associated with mangrove roots (Rhizophora mangle, Avicennia germinans, Laguncularia racemosa) was quantified.

Main Results:

• Sediment dinitrogen fixation rates were low and energy-limited, showing increased activity with carbon source addition.
• Litter from Ulva spp., mangrove leaves, and seagrass also supported acetylene reduction.
• Excised and intact mangrove roots exhibited significantly higher nitrogenase activity compared to sediments.
• Root-associated activity was independent of added glucose, suggesting utilization of root exudates.

Conclusions:

• Dinitrogen fixation in Tampa Bay mangroves is primarily associated with root systems.
• Mangrove rhizoplane bacteria are capable of utilizing root exudates for dinitrogen fixation.
• Energy limitation is a key factor for nitrogenase activity in mangrove sediments.