Effects of hydroxyapatite and modified biochar derived from Camellia oleifera fruit shell on soil Cd contamination and N2O emissions

Heavy metal pollution and global climate change caused by increased greenhouse gas emissions are two important challenges to sustainable development. Various strategies have been implemented to mitigate both heavy metal pollution and global climate change, including the use of biochar obtained from biorefinery of agroforestry biowaste . This study was conducted to clarify how nitrous oxide (N 2 O) emission and soil cadmium (Cd) contamination respond to mitigation strategies, aiming to understand which strategy will be efficient in mitigating both N 2 O emissions and Cd contamination. Effects of three soil conditioners (biochar; modified biochar, MB; hydroxyapatite , HAP) and Cd on N 2 O emissions from acid soil of Camellia oleifera plantations with nitrogen, and microbial functional genes related to N 2 O productions were examined. The results showed that Cd was decreased by 73.4% and 64.9% by HAP in control and fertilized soil, respectively. HAP reduced both Cd and N 2 O emissions more efficient compare to MB and biochar, which strongly associated with increased pH. Soil N 2 O emissions from fertilized soil without Cd were reduced by 91.0%, 34.3% and 25.8% by HAP, MB and biochar, respectively. However, soil N 2 O emissions with Cd were reduced by 67.3% and 24.6% by HAP and MB, respectively, while they were increased by 56.7% by biochar. Cd inhibited N 2 O emissions, via decreasing abundance of ammonia-oxidizing archaea in fertilized soil. Thereby, MB should be considered in amelioration of Cd-contaminated common soil, while HAP could be used in highly acid Cd-contaminated soil, which largely increase soil pH and simultaneously mitigated N 2 O emissions. • Both Cd contamination and N 2 O emissions are environmental issues need to control. • Both biochar and hydroxyapatite decrease and increase soil Cd and pH, respectively. • Modified biochar has stronger adsorption and ion exchange capacity than biochar. • Modified biochar mitigates more N 2 O emissions than common biochar. • HAP mitigated soil Cd contamination and N 2 O emission, and largely increase soil pH.