Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature, pH, organic carbon, and substrates

Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N production in a paddy soil were investigated via slurry incubation combined withN tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g h) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g h). The presence of glucose and acetate (5-100 mg C L) significantly inhibited anammox activities and the ratio of anammox to total N production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (V) of 4.4 nmol N g h and an affinity constant (K) of 6.3 mg NH-N L. Whereas, nitrate addition (5-15 mgNO-N L) significantly inhibited anammox activities and the ratio of anammox to total N production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.