Shaping rhizocompartments and phyllosphere microbiomes and antibiotic resistance genes: The influence of different fertilizer regimes and biochar application

Understanding the impact of different soil amendments on microbial communities and antibiotic resistance genes (ARGs) dissemination is crucial for optimizing agricultural practices and mitigating environmental risks. This study investigated the effects of different fertilizer regimes and biochar on plant-associated bacterial communities and ARGs dissemination. The biochar's structural and chemical characteristics were characterized using scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy, revealing a porous architecture with diverse functional groups. The presence of ARGs varied significantly across groups, with manure-treated samples exhibiting the greatest diversity and abundance, raising concerns about ARGs dissemination. Soil enzyme activities responded differently to treatments; manure significantly enhanced catalase, acid phosphatase, and urease activities, whereas saccharase was most responsive to chemical fertilizer. These differences are possibly responsible for the distinct microbiome structure associated with the plant's root system. The analysis of bacterial diversity and richness across rhizocompartments and the phyllosphere highlighted that manure-treated rhizospheres and phyllospheres displayed the highest species richness and diversity. Notably, Proteobacteria dominated across most treatments, with distinct shifts in bacterial phyla and genera influenced by manure and biochar applications. The LEfSe analysis identified key indicator genera specific to each group, indicating that both fertilizer type and biochar application significantly shape microbial community composition. Co-occurrence network analysis further demonstrated that manure and biochar treatments created unique microbial networks in the rhizosphere, rhizoplane, phyllosphere, and endosphere, highlighting the role of these amendments in modulating microbial interactions in plant-associated environments. These findings suggest that manure, while enhancing microbial diversity and soil enzyme activities, also increases ARGs, whereas biochar may not contribute to the spread of ARGs and fosters distinct microbial communities, offering valuable insights for sustainable agricultural practices.