Population characteristics and influential factors of nitrogen cycling functional genes in heavy metal contaminated soil remediated by biochar and compost.

Sixteen treatments of soil contaminated by Cu, Pb, and Zn by the addition of a different percentage of biochar and compost were incubated for 120 days. The abundance of denitrifying genes such as narG, nirK, nirS and nosZ and the ammonia-oxidizing amoA genes of ammonia-oxidizing archaea/bacteria (AOA/AOB), soil nitrite reductase activity (S-NiR) and their shaping factors were also determined. The relationships between functional genes, S-NiR, and physico-chemical parameters were analyzed using the Pearson correlation method. The study found that the changes in physico-chemical parameters, including water-soluble organic carbon (WSC), nitrate (NO) and ammonium (NH), were predominant in different treatments. The abundance of nirK and narG genes is most sensitive to the changes in the properties of the soil sample. Bacterial 16S rDNA gene abundance was significantly affected by NO and S-NiR (P < 0.05). Nitrifying genes were mainly correlated to WSC and S-NiR, while denitrifying genes were associated with pH, electrical conductivity, NO and S-NiR. The systematic study for the relationship between the genes and the environmental parameters will help us to deep understand the biological mechanisms of nitrogen cycle in heavy metal contaminated soils remediated by biochar and compost.