Dissimilatory nitrate reduction to ammonium increased with rising temperature

Although recent studies have explored dissimilatory nitrate reduction to ammonium (DNRA), little is known about the dependence of this process on temperature. A laboratory experiment was conducted to investigate if temperature regulates nitrate (NO3ˉ) reduction by DNRA and denitrification. Soil samples were incubated at 10 to 40 °C for 28 days, and 15N tracer methods were applied to estimate the reduction of 15NO3ˉ to 15NH4+ by DNRA organisms and to 15N2O or 15N2 by denitrifiers. Raising the temperature from 10 to 40 °C increased DNRA, which contributed to enrichment of the NH4+ pool, particularly at 40 °C. The percentage of 15NO3ˉ reduced by DNRA was from 4 to 30% of that reduced by denitrification, and decreased with increasing temperature. DNRA and denitrification were positively correlated with the abundance of nrfA and nosZ genes, respectively. The accumulation of 15NH4+ slowed in the final 12 h of sampling times, which may be due to a re-conversion of 15NH4+ to 15NO3ˉ by nitrification. High temperatures (30 to 40 °C) enhanced 15N2 production, which suggests that temperature plays an important role in regulating complete denitrification from NO3ˉ to N2.