Emergent macrophytes act selectively on ammonia-oxidizing bacteria and archaea

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Wetland Biogeochemistry

Background:

• Ammonia oxidation is a key step in nitrogen cycling in aquatic ecosystems.
• Both bacteria and archaea perform ammonia oxidation, but their relative abundance varies with environmental conditions.
• Coastal wetlands are important nitrogen sinks and harbor diverse microbial communities.

Purpose of the Study:

• To quantify ammonia-oxidizing bacteria (AOB) and archaea (AOA) in sediments and on macrophyte roots in coastal wetlands.
• To investigate the factors influencing the distribution and abundance of AOB and AOA in these environments.
• To determine if plant roots create conditions that favor either AOB or AOA.

Main Methods:

• Quantification of AOB and AOA using targeting the amoA gene via quantitative PCR.
• Sampling of sediments and roots from dominant macrophytes across eight coastal wetland sites.
• Analysis of bacterial-to-archaeal amoA gene ratios in relation to environmental parameters like ammonium levels and pH.

Main Results:

• AOA were the dominant ammonia oxidizers in most bulk sediment samples.
• The ratio of bacterial to archaeal amoA gene copies increased with higher ammonium concentrations and pH in sediments.
• This bacterial-to-archaeal ratio was significantly higher on the root surfaces compared to bulk sediments for all plant species studied.

Conclusions:

• Plant root surfaces in coastal wetlands create a distinct microenvironment that favors the enrichment of ammonia-oxidizing bacteria (AOB) over archaea (AOA).
• This suggests that macrophyte roots play a crucial role in modulating ammonia oxidation pathways in nitrogen-rich wetland soils.
• Understanding these microbial dynamics is vital for comprehending nitrogen cycling and overall wetland ecosystem functioning.