Effect of Sewage Sludge Biochar (SSB) on the Root Bacterial Community of Strawberry (Fragaria × ananassa): A 16S rRNA Gene Sequencing Approach

Strawberry (<i>Fragaria × ananassa</i>) is one of the most consumed berries worldwide. Despite improvements in management practices and breeding, maintaining soil health and minimizing environmental impact remain a challenge for agricultural systems. Biochar has been proposed as an effective strategy to mitigate climate change, enhance soil health, and promote plant growth. This study investigated the effects of sewage sludge biochar (SSB; 0% control, 5%, and 10% <i>w</i>/<i>w</i>) on the root-associated bacterial community of strawberry plants grown in pots under greenhouse conditions. Results obtained using 16S rRNA gene sequencing revealed a stable core bacterial community comprising 1207 amplicon sequence variants (ASVs), representing 13.2% of all detected ASVs and shared across all treatments. In contrast, biochar-amended soils harbored distinct sets of unique ASVs, with 1795 ASVs (19.7%) in the 5% SSB treatment and 2097 ASVs (23.0%) in the 10% SSB treatment, indicating treatment-specific community differentiation. Phylum-level analysis showed that Cyanobacteriota and Proteobacteria dominated the root-associated bacterial communities across all treatments, with no significant differences between biochar-amended soils and control groups. Alpha diversity did not differ significantly among treatments (<i>p</i> > 0.05), but beta diversity indicated subtle shifts in bacterial community composition under SSB amendment. SSB application increased community homogeneity, while overall bacterial diversity remained unchanged, indicating bacterial community restructuring rather than functional enhancement.