Effect of tillage state of paddy soils with heavy metal pollution on the nosZ gene of N2O reductase.

• The nosZ gene of N 2 O reductase determined by paddy soil tillage state. • The clade Ⅱ and Ⅰ nosZ gene was dominated in the tillage and fallow period, respectively. • Heavy-metal pollution inhibited the N 2 O emission while not affecting the genes' switch. • The genus Bradyhizobium most significantly regulated the N 2 O flux. Paddy soils are an important source of atmospheric nitrous oxide (N 2 O). However, numerous studies have focused on N 2 O production during the soil tillage period, neglecting the N 2 O production during the dry fallow period. In this study, we conducted an incubation experiment using the acetylene inhibition technique to investigate N 2 O emission and reduction rates of paddy soil profiles (0-1 m) from Guangdong Province and Jinlin Province in China, with different heavy-metal pollution levels. The abundance and community structures of denitrifying bacteria were determined via quantitative -PCR and Illumina MiSeq sequencing of nosZ, nirK , and nirS genes. Our results showed that the potential N 2 O emission rate, N 2 O production rate, and denitrification rate have decreased with increasing soil vertical depth and heavy-metal pollution. More importantly, we found that the functional gene type of N 2 O reductase switched with the tillage state of paddy soils, which clade Ⅱ nosZ genes were the dominant gene during the tillage period, while clade Ⅰ nosZ genes were the dominant gene during the dry fallow period. The heavy-metal pollution has less effect on the niche differentiation of the nosZ gene. The N 2 O emission rate was significantly regulated by the genus Bradyhizobium , which contains both N 2 O reductase and nitrite reductase genes. Our findings suggests that the nosZ gene of N 2 O reductase can significantly impact the N 2 O emission from paddy soils. [Display omitted] [ABSTRACT FROM AUTHOR]