Temperature affects the kinetics of nitrite oxidation and nitrification coupling in four agricultural soils

摘要

The oxidation of ammonia (NH3) to nitrite (NO2-) by archaea and bacteria (AOA and AOB) in soil has been studied intensively for > 140 y. However, relatively little attention has been focused on the activity of nitrite oxidizing bacteria (NOB), which catalyze the oxidation of NO2-, despite ample published evidence of soil NO2- accumulation, and the temperature dependent accumulation of NO2- in wastewater and aquatic environments. This study evaluated the response of NO2- oxidizing activity to temperature in four Oregon agricultural soils. Rates of NO2- oxidizing potentials (NOP) were measured at 4-42 degrees C in all soils. Evaluation of the thermodynamic parameters found that the NOB have a similar temperature range and optimal temperature as the NH3 oxidizer response observed in Taylor et al. (2016). A determination of kinetic parameters of NO2- oxidation at 17, 30, and 37 degrees C found a trend for the apparent maximum velocity (V-max) to be greater at 30 than 17 degrees C, and significant, soil-specific changes in substrate affinity (K-m ) of NO2- consumption. Although the potential rates of NO2- oxidation exceeded those of NH3 oxidation, NO2- accumulated under at least one temperature in all soils. There were only weak correlations between NO2- accumulation and rates of NH3 or NO2- oxidation, the abundance of Nitrobacter nxrA or Nitrospira nxrB genes or the total (nxrA + nxrB)/amoA gene ratio. The apparent K-m did not correlate with NO2- accumulation at any temperature; however, utilizing the obtained V-max and K-m we found that Michaelis-Menten kinetics predict that an accumulation of measurable NO2- is required to drive equal rates of NH3 and NO2- oxidation. Implications of reductions in NO2- affinity by NOB at some temperatures that result in increased NO2- accumulation in soils include plant toxicity and the loss of soil N through increased production of reactive N-oxide gases.