[Effects of Biochar on Nitrous Oxide Fluxes and the Abundance of Related Functional Genes from Agriculture Soil in the North China Plain].

To explore the effect and mechanism of biochar application in reducing nitrous oxide (NO) content in agricultural soil, from March 27 to June 5 2015, pot experiments were conducted to study the effects of biochar application rates (CK, C1:5%, C2:10%, C3:15%, and C4:30%) (mass fraction) on soil NO fluxes and the functional marker genes ammonia monooxygenase (), , and , which are responsible for nitrification and denitrification. The results revealed the following. ①The application of low doses of biochar (5%) promoted NO emission. The application of middle and high doses of biochar reduced NO emission. Furthermore, the application of biochar (15%) was found to be the best practice to reduce NO emission. ② At the beginning of the experiment, biochar had a significant effect on the abundance of soil and denitrification bacteria gene. Furthermore, the abundance of AOA and had a significant positive correlation with the biochar rate, and the abundance of gene and biochar rate were significant. There was a significant negative correlation between AOB and gene abundance and biochar rate. At the end of the experiment, AOA abundance correlated negatively with biochar rate, while there was a significantly positive relationship between AOB abundance and biochar rate. ③ At the beginning of the experiment, the NO fluxes exhibited a significant negative correlation with AOA and gene, indicating that NO production was controlled by the abundance of AOA and gene under high soil moisture content. At the end of the experiment, there was a significant positive correlation between NO flux and gene, indicating that the production of NO was regulated by the abundance of gene under low soil water content. The results of this study showed that the application of biochar altered the abundance of and denitrification bacteria genes, and reduced NO emission. These results provide a theoretical basis for a rational application of biochar in farmland.