The rhizosphere as a hotspot for nitrite- and nitrate-dependent anaerobic oxidation of methane in paddy fields

A novel combination of carbon and nitrogen cycling occurs through nitrite- and nitrate-dependent anaerobic oxidation of methane (AOM). However, their role in the rice rhizosphere remains unexplored. This study investigates the contribution and regulation of nitrite- and nitrate-AOM in the rhizosphere soil of paddy fields. The results showed that nitrite- and nitrate-AOM activities were elevated in rhizosphere soil by 132 % and 87 %, respectively, compared to bulk soil across all fertilization treatments. Rhizosphere soil exhibited a significantly higher abundance of NC10 bacteria (9.89 × 10⁶-2.04 × 10⁷ copies g^-1 dry soil) than bulk soil (1.50-2.94 × 10⁶ copies g^-1 dry soil). High-throughput sequencing unveiled distinct community compositions of NC10 bacteria and ANME-2d archaea in rhizosphere and bulk soils. Furthermore, PLS-PM analysis identified that significant variations in soil properties between rhizosphere and bulk soils resulted in the difference of NC10 bacterial abundance, finally leading to the difference in nitrite-AOM activity. However, nitrate-AOM activity was collectively influenced by the variations in soil properties and the abundance of ANME-2d archaea. This study provides pioneering evidence, positioning the rhizosphere as an active region for AOM, thereby refining the evaluation of AOM's role in paddy fields.