Modeling of soil nitrification responses to temperature reveals thermodynamic differences between ammonia-oxidizing activity of archaea and bacteria.

Soil nitrification potential (NP) activities of ammonia-oxidizing archaea and bacteria (AOA and AOB, respectively) were evaluated across a temperature gradient (4-42 °C) imposed upon eight soils from four different sites in Oregon and modeled with both the macromolecular rate theory and the square root growth models to quantify the thermodynamic responses. There were significant differences in response by the dominant AOA and AOB contributing to the NPs. The optimal temperatures (Topt ) for AOA- and AOB-supported NPs were significantly different (P<0.001), with AOA having Topt >12 °C greater than AOB. The change in heat capacity associated with the temperature dependence of nitrification (ΔCP ‡ ) was correlated with Topt across the eight soils, and the ΔCP ‡ of AOB activity was significantly more negative than that of AOA activity (P<0.01). Model results predicted, and confirmatory experiments showed, a significantly lower minimum temperature (Tmin ) and different, albeit very similar, maximum temperature (Tmax ) values for AOB than for AOA activity. The results also suggested that there may be different forms of AOA AMO that are active over different temperature ranges with different Tmin , but no evidence of multiple Tmin values within the AOB. Fundamental differences in temperature-influenced properties of nitrification driven by AOA and AOB provides support for the idea that the biochemical processes associated with NH3 oxidation in AOA and AOB differ thermodynamically from each other, and that also might account for the difficulties encountered in attempting to model the response of nitrification to temperature change in soil environments.