Soil texture shapes biochar-induced shifts in microbial communities and severity of potato common scab

Biochar is widely recognized for its potential to enhance soil carbon, yet its influence on soil chemistry, microbial communities, and plant disease dynamics remains uncertain. This study explored how biochar affects the severity of common scab, a globally significant potato disease, through its interactions with soil properties and microbial communities. Two contrasting soils planted with potatoes were amended with fresh biochar and biochar aged within the soils for one and two years. Bulk and tuberosphere soil samples were analyzed for nutrient and micronutrient availability, microbial community composition using 16S rRNA gene amplicon sequencing and basal respiration. In sandy soil V, biochar induced immediate but transient shifts in soil chemistry and microbial structure, while in silty soil Z, changes emerged gradually and intensified with biochar aging. These dynamics mirrored the progression of common scab severity, suggesting a strong link between nutrient availability, microbial community shifts, and disease outcomes. The contrasting responses of the two soils were attributed to differences in cation exchange capacity and particle size, which influenced nutrient retention and microbial community structure, including populations of pathogenic Streptomyces. Notably, the exchangeable surface area of soil particles emerged as a factor modulating biochar effects on disease severity. These findings highlight the importance of considering soil texture and microbial composition when applying biochar, emphasizing that site-specific characteristics can critically shape biochars impact on plant health. ImportanceBiochar is increasingly used to improve soil quality and health, but its effects on plant diseases are not fully understood. This study showed that biochar can either reduce or worsen common scab of potatoes depending on soil type. By examining how biochar changes soil chemistry, nutrient availability and microbial communities, we found that soil texture and nutrient exchange capacity influence the disease outcomes. In silty soil, biochar decreased nutrient availability and promoted pathogenic bacteria that cause common scab, while in sandy soil, it did not. These findings highlight the need to consider local soil conditions before applying biochar in agriculture. Understanding how soil properties influence microbial responses helps farmers and researchers make better decisions to protect crops and improve soil health.