Biochar‐Induced Shifts in Fungal Community Structure and Their Association With Soil Physical Properties in Degraded Soil From the Brazilian Semiarid

ABSTRACT Soil degradation compromises ecosystem functioning. Biochar, a carbon‐rich amendment, has gained attention as a promising strategy to enhance soil structure and restore microbial balance. This study investigated the effects of two biochars, cashew bagasse biochar (CBB) and a co‐pyrolyzed biochar produced from sewage sludge and cashew pruning residues (SPB), on the physical properties and the fungal community structure in a severely degraded semiarid soil. A greenhouse experiment was conducted with four biochar application rates (5, 10, 20, and 40 Mg ha −1 ) and a control. The fungal community was characterized using 18S rRNA gene sequencing and evaluated through diversity metrics, correlation analyses, and co‐occurrence network modeling. CBB preserved the dominance of Ascomycota and promoted gradual diversification, whereas SPB induced more pronounced taxonomic shifts, increasing the relative abundance of Mucoromycota and Basidiomycota . Fungal α‐diversity and network complexity peaked at 20 Mg ha −1 , suggesting that intermediate dosages enhanced habitat heterogeneity and nutrient availability. At higher doses, both indices declined, likely due to environmental stress or nutrient overload. Overall, biochar application shaped fungal community composition and showed selective links with soil physical attributes, with CBB increasing macroporosity and contributing to shifts in aggregate‐size distribution. In contrast, SPB exerted stronger chemical influences, notably elevating soil Zn, thereby creating a trace‐metal gradient that filtered fungal taxa. Correlation analyses further revealed that key fungal groups responded strongly to soil structural domains, particularly pore‐size distribution and aggregate fractions, highlighting that each biochar operates through distinct mechanistic pathways that modulate both physical habitat and fungal ecological assembly.