Enhanced Nitrogen Use Efficiency and Reshaped Phyllosphere Microbiome through Biochar Application and Nitrogen Fertilizer Reduction

Paper mulberry (<i>Broussonetia papyrifera</i>), a high-protein forage species, exhibits low nitrogen use efficiency (NUE) under conventional nitrogen fertilization. This study conducted a field experiment to systematically evaluate the effects of coapplying biochar with reduced nitrogen fertilizer on paper mulberry by integrating plant physiological measurements, soil property analysis, and phyllosphere microbiome profile. Results demonstrated that moderate biochar addition significantly enhanced plant growth, forage quality, and soil health, while improving NUE. Notably, coapplying biochar with a 15% reduced nitrogen emerged as a sustainable fertilization strategy, reducing nitrogen inputs without compromising plant performance. 16S rRNA gene sequencing revealed that biochar treatment reshaped the phyllosphere microbiome by increasing diazotroph abundance, suppressing pathogens, and enhancing microbial network complexity. Overall, this study demonstrates that coapplying biochar with 15% reduced nitrogen not only improves NUE, but also enhances plant performance and soil properties, while reshaping the phyllosphere microbiome into a more plant-beneficial community.