Modeling Soil Nitrification Responses to Temperature in Cropped and Noncropped Oregon Soils.

Soil nitrification potential (NP) activities of ammonia oxidizing archaea and bacteria (AOA and AOB, respectively) were evaluated across a temperature gradient (4 – 42^oC) imposed upon eight soils from four different sites in Oregon and modeled with both the macromolecular rate theory (MMRT) and the square root growth (SQRT) models to quantify the kinetic responses. The optimal temperatures (T_opt) for AOA and AOB supported NPs were significantly different (p < 0.001), with AOA having T_opt >10^oC greater than AOB. The change in heat capacity associated with the temperature dependence of nitrification (ΔC_P^‡) was correlated with T_opt across the eight soils, and the ΔC_P^‡ of AOB activity was more negative than that of AOA activity. Model results predicted, and confirmatory experiments showed, a significantly lower minimum temperature (T_min) for AOB than for AOA activity, but no differences in their maximum temperature. The results also suggested there were at least two AOA subgroups with different T_min, but no evidence of multiple T_min 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.