[Effects of Biochar Amendment on N₂O Emission and Its Functional Genes in Pepper Growing Soil in Tropical Areas]

Biochar application may mitigate N₂O emissions and increase crop yield, yet little is known about microbial dynamics variation. To investigate the potential of increasing yield and reducing emissions of biochar in tropical areas and the dynamic mechanism of related microorganisms, a pot experiment was conducted to investigate the biochar application on pepper yield, N₂O emissions, and dynamic variation of related microorganisms. Three treatments were applied:2% biochar amendment (B), conventional fertilization (CON), and no nitrogen (CK). The results showed that the yield of the CON treatment was higher than that of the CK treatment. Compared with that of the CON treatment, biochar amendment significantly increased the yield of pepper by 18.0% (P<0.05), and biochar amendment could increase the content of NH⁺₄-N and NO^-₃-N in soil in most periods of pepper growth. Compared with that in the CON treatment, the B treatment significantly reduced cumulative N₂O emissions by 18.3% (P<0.05). Ammonia oxidizing archaea (AOA)-amoA and ammonia oxidizing bacteria (AOB)-amoA were very significantly negatively correlated with N₂O flux (P<0.01). N₂O flux was significantly negatively correlated with nosZ gene abundance (P<0.05). This indicated that N₂O emission may have mainly resulted from the denitrification process. In the early stage of pepper growth, biochar significantly reduced N₂O emissions by reducing the value of (nirK+nirS)/nosZ, whereas in the late stage of pepper growth, the value of (nirK+nirS)/nosZ of the B treatment was higher than that of the CON treatment, resulting in higher N₂O flux in the B treatment. Therefore, biochar amendment could not only increase vegetable production in tropical areas but also reduce N₂O emissions, which can be used as a new strategy to improve soil fertility in Hainan Province and other tropical areas.