The dose-dependent effects of dissolved biochar on C. elegans: insights into the physiological and transcriptomic responses

Abstract As the benefits of biochar amendment for soil remediation have been widely recognized, the potential risk of downward nematode migration has received increasing attention. Dissolved biochar (DBC) is an essential component of biochar that is easily absorbed and utilized by organisms. However, the effect of DBC on nematodes remains unclear. This study aimed to assess the effect of DBC on Caenorhabditis elegans . The response of C. elegans to different DBC concentrations (0, 250, 500, and 1000 mg L −1 ) was investigated using culture assays and RNA-seq analysis. The results revealed a hormetic effect of DBC, with low concentrations (250–500 mg L −1 ) promoting growth and high concentrations (≥ 1000 mg L −1 ) inhibiting growth. Meanwhile, DBC affected nematode movement and neuromuscular function. Transcriptome analysis revealed a dose-dependent increase in the number of differentially expressed genes (DEGs), with key changes related to metabolism, the stress response, and cellular processes. Weighted gene coexpression network analysis (WGCNA) revealed that gene modules, such as dyf-11 , ins-16 , and hsp-12.6 , were strongly correlated with traits such as body size and reproduction. Additionally, genes involved in ciliary function, insulin signaling, and neurotransmitter biosynthesis were affected, highlighting the impact of DBC on growth and movement regulation. These findings suggest the need to carefully manage biochar application in agriculture to balance its benefits and potential risks to soil organisms like nematodes. Graphical Abstract