Microbial pathways for nitrogen loss in an upland soil.

Area of Science:

• Environmental Microbiology
• Soil Science
• Biogeochemistry

Background:

• Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are crucial nitrogen cycling processes in aquatic environments.
• Their ecological significance in agricultural upland soils remains under-investigated.

Purpose of the Study:

• To investigate the spatio-temporal distribution and activity of anammox and n-damo bacteria in agricultural upland soil profiles.
• To determine the contribution of these processes to nitrogen loss compared to denitrification and dissimilatory nitrate reduction to ammonium (DNRA).

Main Methods:

• Soil core sampling to a depth of 300 cm from an agricultural upland.
• Nitrogen conversion activity monitoring using isotope-tracing techniques over one year.
• Phylogenetic analysis of anammox bacteria communities.

Main Results:

• Denitrification was the predominant nitrogen loss pathway in surface soils (0-20 cm), accounting for 99.0% in winter and 85.0% in summer.
• Anammox contributed significantly to nitrogen loss below 20 cm depth (79.4% in winter, 65.4% in summer), with n-damo not detected.
• Dissimilatory nitrate reduction to ammonium (DNRA) played a minor role in surface soils but increased significantly below 80 cm depth.

Conclusions:

• Denitrification remains the primary nitrogen loss process in the overall soil profile of agricultural uplands.
• Anammox is a significant nitrogen loss pathway in deeper soil layers, with distinct bacterial communities at different depths.
• Ammonium oxidation and nitrate reduction are key factors influencing anammox and denitrification rates at varying soil depths.