Relative Sensitivity of Soil Nitrifiers to Zinc: A Comparison of Heterotrophic and Autotrophic Nitrification Potentials.

Trace elements naturally occur in the environment, and, when in sufficient concentrations can be toxic to soil organisms. Anthropogenic activity often leads to increases in surface metal concentrations. Soil nitrification is the central pathway in the nitrogen cycle, and is the most sensitive soil microbial process to trace element addition.  Soil nitrification potentials are often therefore used as international standards for measuring the effects of various environmental stressors. However there are several different methods for determining nitrification rates in soils and no standard method is universally accepted. Ammonium oxidation is the rate limiting step in the nitrification process, and has been intensively studied for its sensitivity to environmental stressors. Potential ammonium oxidation is an estimate of the production of nitrite in soils and is a determination of enzymatic activity. Changes in the activity of different ammonium oxidisers can be studied if the ammonium oxidisers responsible can be separated. Nitrapyrin is the longest know and most commonly used inhibitor of chemolthotrophic nitrification. This study aimed to determine the relativity sensitivity of heterotrophic and chemolthotrophic nitrification to trace metal stress in the form of zinc sulphate additions. Heterotrophic and total ammonium oxidation potentials were determined for artificially contaminated boreal forest soils. Soils were artificially contaminated with zinc to concentrations ranging from 74-3000 mg kg-1. This studied highlights the ability to differentiate between nitrifiers in soils with the use of an inhibitor, and the differences in there sensitivity to zinc stress.