Environmental Factors Controlling Dissimilatory Nitrate Reduction to Ammonium in Paddy Soil

Dissimilatory nitrate reduction to ammonium (DNRA) is of great significance in rice paddies since its considerable influence on nitrogen (N) conservation. The present study provided specific information on the relationship between environmental factors and DNRA rates in a typical paddy soil. Five batches of incubation experiments were conducted in the paddy soil, employing the soil slurry-based (15) N tracer technique. The effects of different environmental factors, including temperature (5, 15, 20, 25, and 35celcius), pH (3.1, 5.5, 9.2, and 10.9), reduced iron content (300, 500, 800, and 1000 mu mol L-1 Fe2+), carbon/nitrogen ratio (C/N, 2.5-30), and dissolved organic carbon/nitrate ratio (DOC/NO3-, 0.25-5), on the DNRA rate were investigated. The results showed that DNRA occurred at temperatures ranging from 5 to 35celcius, with the rate increasing exponentially as the temperature was elevated. The DNRA rate reached its maximum at a pH of 7.3 (2.29 nmol N g(-1) h(-1)). The addition of ferrous iron (Fe2+) at 800 mu mol L-1 significantly (P < 0.05) stimulated the DNRA rate. The increase in the C/N ratio to > 12 promoted DNRA rates significantly (P < 0.05). Along with the increase in DOC/NO3- ratio, DNRA rates went up significantly (P < 0.05). Our results provide valuable information on the environmental factors which regulate DNRA in paddy soil, highlighting the impact of both supply and availability of organic C on the DNRA rate.

Automated summary

This study provides specific information on the relationship between environmental factors and DNRA rates in rice paddies. The results show that temperature, pH, reduced iron content, C/N ratio, and DOC/NO3- ratio significantly influence the DNRA rate.