Afforestation inhibits aromatic ring cleavage and promotes soil organic carbon sequestration in seasonally flooded marshland soils at 1-m depth in China

Afforestation stimulates the degradation or sequestration of soil organic C (SOC). While the role of complex plant-derived components such as lignin phenol in enhancing SOC storage post-afforestation is acknowledged, the underlying mechanism remains largely unexamined. In this study, we focused on the genes responsible for the cleavage of aromatic rings of plant lignin phenol, at 1-m depth soil in a periodically inundated wetland afforested with poplar trees along the Yangtze River in China. Our findings indicated that afforestation led to a noticeable increase in both SOC and lignin phenol contents in the subsoil, as opposed to non-afforested areas (P < 0.001). There was a significant reduction in the prevalence of CAZymes and genes involved in aromatic ring cleavage post-afforestation (P < 0.001). The accumulation of SOC and plant lignin phenol was found to be negatively correlated with genes associated with aromatic ring cleavage, respectively. Afforestation with poplar trees in wetlands was found to prevent the loss of SOC in the subsoil by reducing the abundance of genes associated with aromatic ring cleavage and hindering the breakdown of lignin phenol, resulted from the low O₂ content and narrowed niche environment. This research sheds light on the processes that give rise to the sequestration of SOC following afforestation and offers novel perspectives for the study of lignin phenol and the dynamics of SOC across broader environmental contexts.