Particle size influences biochar-mediated control of pepper Phytophthora blight: linking released compounds to soil microbial disease suppression

Abstract Biochar is a promising soil amendment for controlling plant diseases, but the influence of its particle size on disease suppression remains unclear. This study focused on the differential mechanisms of fine and coarse biochars in controlling pepper Phytophthora blight, linking biochar-released compounds (BRCs) to soil microbial disease suppression. The pot experiment revealed that fine biochar provided a stronger initial suppression of disease severity and pathogen abundance, but these effects diminished over time, whereas coarse biochar provided a more durable control effect. Similar time-dependent effects were observed for the increase in total and biocontrol microbial abundances. The mesh-bag experiment confirmed that fine biochar rapidly released minerals and labile organic carbon (LOC) in the early stage. This initial release significantly increased the abundances of total bacteria, total fungi, Pseudomonas , Trichoderma , and Penicillium , as well as the antagonist percentages of total bacteria and fungi, while suppressing Phytophthora capsici . However, the reduced release of BRCs in the later stage markedly weakened these effects. In contrast, coarse biochar provided more durable suppression through a slower, more sustained release of BRCs, resulting in a greater improvement in microbial properties during the later stage. Mantel tests and PLS-PM analysis indicated that electrical conductivity (representing minerals) and LOC were the key drivers that enhanced microbial abundance and antagonism, which in turn effectively suppressed the pathogen. This study reveals that biochar particle size influences the release rate of BRCs, resulting in a time-dependent control effect. These findings provide new insights into developing precise and sustainable disease control strategies. Graphical Abstract