Response of N2O emission and denitrifying genes to iron (II) supplement in root zone and bulk region during wetting-drying alternation in paddy soil.

Ferrous (Fe (II)) plays a key role in the production or consumption of N 2 O through biochemical pathways in paddy soil. Drying-wetting alternations can affect Fe cycling and the associated N 2 O emissions, however, the underlying microbial mechanisms remain largely unknown, particularly in plant systems with the presence of roots. In this study, a laboratory experiment with four Fe (II) levels (0, 50, 150, and 300 mg Fe (II) kg−1 dry soil) was conducted to investigate the response of N 2 O emission and denitrifying genes to iron (II) supplement in root zone and bulk region during wetting-drying cycles in paddy soils. The results indicated that supplemented Fe (II) led to a reduction in soil N 2 O emissions, predominantly observed during the drying phase. The bulk soil exhibited higher N 2 O fluxes compared to root zone. However, the decrease in cumulative N 2 O (cumul-N 2 O) by Fe (II) was significantly greater in bulk region than in root-affected soil (P < 0.001), registering 85–91 % reduction for soils amended with low to medium rates (50 and 150 mg Fe (II) kg−1 dry soil) throughout the experiment. This might be attributed to the more sensitive response of N 2 O reductase (nosZ gene) to low or medium Fe (II) supplementation in bulk soil than in root zone. The highest Fe (II) addition (300 mg Fe (II) kg−1 dry soil) showed a negative impact on nosZ -containing gene during initial flooding phase, resulting in the lower reduction rate (40 %) in cumulative N 2 O emission from bulk soil. Cross-correlation analysis showed that the changes of nosZ- containing genes in root zone occurred before variations of cumulative N 2 O data, indicating that compared to bulk soil, root zone soil exhibited a more pronounced of N 2 O consumption capability, especially after addition of ferrous. In summary, judicious Fe (II) application into soil promotes N 2 O reduction during wetting-drying alternation. The response of nosZ abundance to Fe (II) supplementation is likely the pivotal microbial factor influencing N 2 O emission reduction during wetting-drying alternation in paddy soil. [Display omitted] • Addition of Fe(II) into paddy soil reduced N 2 O emission during wetting-drying alternation. • Supplemented Fe(II) significantly increased nosZ gene from paddy soil during drying. • The root zone in rice-planted paddy soil might have the stronger capacity of N 2 O consumption. • Relations between N 2 O emission and abundance of denitrifying genes often existed with time lags. [ABSTRACT FROM AUTHOR]