Effect of carbonized apple wood on nitrogen‐transforming microorganisms and nitrogen oxides in soil of apple tree root zone

Abstract

Biochar amendment is commonly used to mitigate anthropogenic greenhouse gas emissions of agricultural soil. A new type of biochar, carbonized apple wood (CAW), was applied at different rates (0, 5, 10, 20 and 40 g kg−1) to the soil of 2‐year‐old apple trees (Malus domestica Borkh. cv. Fuji) grown in pots. The variation in soil abundance of functional genes involved in microbial ammonia oxidation (Anammox and amoA) and denitrification (nirS and nirK) was determined by quantitative PCR, and the nitric oxide (NO) and nitrous oxide (N2O) concentrations in the treated soil were analysed using microelectrodes. The soil's microbial biomass carbon, nitrogen and phosphorus increased significantly with 5 and 10 g kg−1 CAW application, and addition of 5–40 g kg−1 CAW altered microbial nitrogen transformation. Furthermore, 5–40 g kg−1 CAW application at 5–20‐cm soil depth reduced NO and N2O concentrations. Redundancy analysis showed close relations between microbial functional genes and soil variables (including microbial biomass carbon, nitric oxide, nitrate nitrogen and nitrite nitrogen) after CAW application. These results indicated that microbial nitrogen transformation varied depending on the amount of CAW applied. Application of a moderate amount of CAW (i.e. 10 g kg−1) reduced the abundance of functional genes involved in microbial nitrogen transformation, suggesting a potential link with the observed reduction in NO and N2O concentrations in the apple root‐zone soil.Highlights Carbonized apple wood (CAW) changed soil microbial nitrogen transformation in apple tree root zone. Application of moderate CAW rates reduced abundances of Anammox, amoA, nirS and nirK genes. Microelectrodes were used to measure nitrous oxides directly in apple root‐zone soil. Moderate rates of CAW reduced soil NO and N2O amounts in the apple tree root zone.