Coconut shell and its biochar as fertilizer amendment applied with organic fertilizer: Efficacy and course of actions on eliminating antibiotic resistance genes in agricultural soil

Biomass amendments have numerous benefits in reducing antibiotic resistance genes (ARGs) in the soil environment. However, there are debatable outcomes regarding the effect of raw biomass and its pyrolytic biochar on ARGs, and the exploration of the influence mechanism is still in infancy. Herein, we investigated the changes in soil ARGs under the organic fertilizer application with coconut shell and its biochar. The results showed that the coconut shell biochar could effectively diminish ARGs, with 61.54% reduction in target ARGs, which was higher than that adding raw coconut shells (p < 0.05). Structural equation modeling indicated that ARGs were significantly affected by changes in environmental factors, mainly by modulating bacterial communities. Neutral community model and network analysis demonstrated that the coconut shell biochar can restrict the species dispersal, thereby mitigating the spread of ARGs. Also, coconut shell biochar exhibited strong adsorption, with a large specific surface area (476.66 m2/g) and pores (pore diameter approximately 1.207 nm, total pore volume: 0.2451 m3/g), which markedly enhanced soil heterogeneity that created a barrier to limit the resistant bacteria proliferation and ARGs propagation. The outcome gives an approach to control the development of ARGs after organic fertilizer application into soil.