Improved Enzyme Kinetic Model for Nitrification in Soils Amended with Ammonium. I. Literature Review

Abstract : Previous research indicates that nitrification in pure cultures can be represented by Michaelis-Menten kinetics. However, the effects of temperature and especially pH have not been treated systematically in any of the previous reviews of the subject. The work reported here is an attempt to synthesize reported temperature and pH effects on nitrification and nitrifier growth rates. In addition we attempt to extend the principles of microbial kinetics to soils. Our work indicates that pH effects can be interpreted mechanistically as inhibitions by hydrogen and hydroxyl ions, nitrous acid, the ammonia. These are incorporated into the Michaelis-Menten expressions. It is also our observation that ammonium oxidizers in natural habitats are characterized by lower Michaelis constants than pure cultures. This is significant particularly in terms of their growth and activity in acid soils. Alternatively, we speculate that proliferation of ammonium oxidizers in acid soils is due to spatial heterogeneity of 'pH' at the microsite level. (Author)