Nitrogen Addition Decreases Dissimilatory Nitrate Reduction to Ammonium in Rice Paddies

This study provides evidence that nitrogen addition reduces nitrogen retention through DNRA and increases nitrogen loss via denitrification in a paddy soil ecosystem. DNRA is one of the major NO3 − reduction processes, and it can outcompete denitrification in NO3 − consumption when rice paddies are low in nitrogen. A significant level of DNRA activity in paddy soils indicates that DNRA plays an important role in retaining nitrogen by reducing NO3 − availability for denitrification and leaching. Our study shows that by reducing N addition to rice paddies, there is a positive effect from reduced nitrogen loss but, more importantly, from the conversion of NO3 − to NH4 + , which is the favored form of mineral nitrogen for plant uptake.