Consumption Capacity of N2O in Paddy Soil and the Response Mechanism of nosZ-I-containing Communities

Abstract

The long-term flooding anaerobic environment in paddy soils is conducive to denitrification, which is one of the most important reasons for N2O emissions. N2O can be transformed to nitrogen gas (N2) by bacteria and archaea containing nitrous oxide reductase (N2OR) encoded by the nosZ gene, which is the only known biological pathway of N2O consumption in soil. nosZ-I is known to be typical in denitrifying bacteria, which is one of the clades of the nosZ gene and is mainly possessed a Tat signal peptide motif. Although many researchers have studied N2O emission characteristics of paddy soil, the capacity of N2O consumption and the response mechanism of related functional microorganisms in paddy fields is not yet clear. To verify the effect of exogenous N2O on N2O consumption and nosZ-I gene, a pot trial experiment was performed under anaerobic conditions. We collected intact soil cores from flooding paddy fields at a 0-5 cm depth, and exogenous N2O gas was input through the bottom of flooding paddy soil cores. Meanwhile, a control treatment (CK) with no additional N2O gas was also performed. The dynamic characteristics of the added exogenous N2O concentration through the intact soil cores, the content of inorganic nitrogen, and DOC were systematically monitored. In addition, the change in the nosZ-I population diversity and community composition were investigated by high-throughput sequencing approaches, with the purpose of revealing the N2O uptake ability of flooded paddy soil and the response mechanism of the nosZ-I population. The results showed that 97.39% of exogenous N2O diffused into the soil cores, and only 0.72%-7.75% of exogenous N2O escaped from the soil surface. The N2O released in the headspace of soil cores could continue being absorbed and consumed by the flooding soil column. In addition, 67.10% of the N2O escaped to the headspace was consumed in exogenous N2O treatment after 192 h of incubation, which was higher than that in CK treatment, and the N2O consumption rate increased by 144.2% than that in CK treatment. Meanwhile, the consumption of NH4+-N, NO3--N, and DOC consumed during exogenous N2O addition treatment was 19.65%, 16.29%, and 8.41% higher than that in CK treatment, respectively. However, the diversity of the nosZ-I gene community had no significant difference; the community composition of nosZ-I-containing bacteria changed significantly after 192 h when exogenous N2O was input. The abundances of OTU5004, OTU5065, OTU960, and OTU1282 (Proteobacteria) significantly increased, which were the dominant bacterial strain of nosZ-I gene on the OTU level. Compared with the initial sample and CK, the abundance of the OTU5004 strain increased by 7.3% and 4.63%, and the abundance of the OTU5265 strain (Azoarcus sp.) increased by 0.33% and 0.15%, respectively. The result indicated that the flooding paddy soil column at the soil layer of 0-5 cm has a strong N2O absorption and consumption ability. In summary, compared with CK, the addition of exogenous N2O significantly accelerated the N2O consumption rate, improved the consumption potential of flooding paddy soil column, promoted carbon and nitrogen conversion, and changed nosZ-I community composition. These results would provide a new reference for reducing atmospheric N2O emissions.