Dissimilatory nitrate ammonification and N(2)fixation helps maintain nitrogen nutrition in resource-limited rice paddies

Abstract

Un-fertilized rice paddies have shown maintained soil nitrogen (N) status, stable N supply to the rice plant and sustained rice yields at moderate levels for hundreds of years. Microbial N2 fixation is known to contribute N to un-fertilized paddies, but it cannot fully explain the maintained N nutrition, where favourable conditions exist for N loss by denitrification. We used 15N tracer, 15N2 uptake, acetylene reduction assay and qPCR to simultaneously investigate N2 fixation, dissimilatory nitrate reduction to ammonium (DNRA), denitrification and related microbial gene abundances in long-term low (or no) and high N input rice paddies of Myanmar. We also determined how varying soil organic c..