To explore the effect and mechanism of biochar application in reducing nitrous oxide (N2O) 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 N2O fluxes and the functional marker genes ammonia monooxygenase (amoA), nirK, nirS, and nosZ, which are responsible for nitrification and denitrification. The results revealed the following. ①The application of low doses of biochar (5%) promoted N2O emission. The application of middle and high doses of biochar reduced N2O emission. Furthermore, the application of biochar (15%) was found to be the best practice to reduce N2O emission. ② At the beginning of the experiment, biochar had a significant effect on the abundance of soil amoA and denitrification bacteria gene. Furthermore, the abundance of AOA and nirS had a significant positive correlation with the biochar rate, and the abundance of nirK gene and biochar rate were significant. There was a significant negative correlation between AOB and nosZ 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 N2O fluxes exhibited a significant negative correlation with AOA and nirS gene, indicating that N2O production was controlled by the abundance of AOA and nirS gene under high soil moisture content. At the end of the experiment, there was a significant positive correlation between N2O flux and nosZ gene, indicating that the production of N2O was regulated by the abundance of nosZ gene under low soil water content. The results of this study showed that the application of biochar altered the abundance of amoA and denitrification bacteria genes, and reduced N2O emission. These results provide a theoretical basis for a rational application of biochar in farmland.
Keywords: agriculture soil; amoA; biochar; nirK; nirS; nitrous oxide; nosZ.