Biochar nanoparticles enhance flowering in Gentiana szechenyii Kanitz. by modulating source-sink carbon allocation and gene expression

Abstract Biochar enhances soil nutrient availability and promotes flowering. Biochar nanoparticles (BCNPs), a key biochar component, migrate into plant tissues to regulate flowering; however, the mechanisms remain unclear. We investigated the impact of biochar on Gentiana szechenyii Kanitz. ( G. szechenyii ) flowering under nutrient-rich conditions. Biochar (18 g) application increased flower number by 24.2%, with no significant changes in soil N, P, K, Mg, S, Si, Zn, and Mn. Transmission electron microscopy showed increased BCNPs accumulation in chloroplasts and higher starch concentration in leaves, while sucrose levels remained unchanged. 13 CO 2 isotope tracing revealed reduced 13 C in leaves and flower branches. Transcriptomic analysis revealed the upregulation of genes involved in sucrose-starch metabolism, flowering regulation, floral meristem development, and hormone. The study shows that BCNPs, after detaching from biochar, migrate into plant tissues and regulate carbon allocation, as well as the expression of flowering- and hormone-related genes, synergistically promoting flowering. BCNPs enhance source activity and sink capacity, with a preferential increase in sink strength, thereby increasing flower number. This study advances the understanding of biochar nanomaterial applications in agriculture. Graphical Abstract