Impact of nitrogen deposition on the microbial activity and composition in forest soils

Emma Thorpe, PhD studentship, University of Essex (2007-2011)

Summary

This study investigates the community composition and activity rates of two important groups of microorganisms- the ammonia oxidisers and the methane oxidising bacteria- at Hockham Heath as well as at a non N-impacted site, Alice Holt, Surrey.

Background

• Hockham Heath at Thetford Forest is characterised by high levels of NH4⁺ deposition due to the proximity of pig and chicken farms.
• A gradient of NH4⁺ and NO3^– has been identified on a 300 m transect through the Corsican Pine and Beech plots.
• Ammonia oxidising bacteria (AOB) and archaea (AOA) are responsible for the first, rate-limiting step in nitrification- ammonia oxidation- which results in the production of NO3^–.
• An increase in NH4⁺ deposition may lead to increased rates of ammonia oxidation and NO3^– production. Whilst NH4⁺ is bound to the soil matrix, NO3^– is soluble and susceptible to leaching, leading to a loss in N from the soil and pollution of surface and groundwater systems.
• Additionally, NH4⁺ and NO3^– have been indicated as inhibitors of methane oxidation.
• Methane oxidation by methane oxidising bacteria (MOB) is the only known biological sink for methane, a potent greenhouse gas.
• It is therefore important to determine the impact of elevated NH4⁺ and NO3^– concentrations on methane oxidation.