Variability in responses of bacterial communities and nitrogen oxide emission to urea fertilization among various flooded paddy soils.

Fertilization affects bacterial communities and element biogeochemical cycling in flooded paddy soils and the effect might differ among soil types. In this study, five paddy soils from Southern China were subjected to urea addition to explore impacts of fertilization on nitrogen oxide (N2O) emission and bacterial community composition under the flooding condition. 16S rRNA gene-based illumina sequencing showed no obvious shifts in bacterial community composition of five soils after urea addition. However, some genera were affected by fertilization addition and the influenced genera varied among soils. During the late period (day 8-19) of flooding incubation without urea addition, N2O emission rates were elevated for all soils. However, urea effects on N2O emission were different among flooded soils. For soils where nirS and nirK gene abundances increased with urea addition, N2O emission was significantly increased compared to control treatment. Redundancy analysis showed that dissolved organic carbon, ammonium (NH4 (+)), ferrous iron (Fe(2+)) and nitrate (NO3 (-)) in pore water explained 33.4% of the variation in soil bacterial community composition, implying that urea regimes influenced the relative abundance of some bacterial populations possibly by regulating soil characteristics and then influencing N2O emission. These results provided insights into soil type-dependent effect of fertilization on the overall bacterial communities and nitrogen oxide emission in flooded paddy soils.