Chain-length-dependent adsorption of extracellular DNA on biochar: Behaviors, mechanisms, and structural Stability

• Short-chain DNA exhibits high adsorption due to its mesoporous accessibility. • Long-chain DNA exhibits great desorption hysteresis because of multisite anchoring. • π–π, H-bonds and hydrophobic interaction are main adsorption mechanisms. • DNA binding to biochar affected its conformation without causing chain fragment. • Molecular simulation confirms stability of DNA with different chain lengths. The environmental fate of extracellular DNA is significantly influenced by its interaction with widely used biochar. However, a systematic understanding of how DNA chain length and biochar properties jointly govern the adsorption process, mechanism, and subsequent DNA stability remains limited. This study systematically investigated the adsorption behaviors and mechanisms of short-stranded (sDNA) and long-stranded DNA (LDNA) on biochars produced at 300 – 600°C under neutral pH conditions. sDNA exhibited a higher adsorption capacity (5.91 mg g -1 on BC600) by accessing internal mesopores on biochar, whereas LDNA showed a lower adsorption (2.22 mg g -1 on BC600) and a stronger desorption hysteresis, resulting from multisite anchoring with biochars. The release rate values of sDNA and LDNA were 5 – 20% and 4 – 13% respectively on BC300. Correlation studies and desorption experiments revealed that π-π interactions and hydrophobic forces were the primary adsorption mechanisms. Spectroscopic analyses and molecular dynamic simulation confirmed conformational changes in the adsorbed DNA but showed no chain fragmentation. These findings underscore that DNA chain length and biochar properties jointly govern the sequestration and stability of DNA, providing essential mechanistic insights for assessing the role of biochar in the persistence and mobility of genetic material in the environment.