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.