Restoration Age Enhances Soil Organic Carbon Sequestration Primarily Through Plant-derived Carbon in a Coastal Wetland

Aims Plant- and microbial-derived carbon (C) are the primary sources of soil organic carbon (SOC) in coastal wetlands, yet their contributions across vegetation restoration chronosequences remain poorly understood. Methods Using biomarker approaches, we investigated the dynamics of total lignin phenols (VSC) and microbial necromass C (MNC) in SOC over a 20-year restoration chronosequence (0, 4, 8, 11, and 20 years) in the Yellow River Delta of China. Results Vegetation restoration significantly increased VSC and MNC contents, but both showed unimodal patterns with age and peaked at 8 years. Restoration age significantly increased VSC contributions to SOC (1.9–7.1%) but had limited effects on MNC, which averaged 28.64%—lower than anticipated. The contents of VSC, MNC, vanillyl phenols, syringyl phenols, cinnamyl phenols, fungal necromass C (FNC) and microbial biomass C (MBC) were positively correlated with SOC content. However, Bacterial necromass C (BNC) showed no significant correlation with SOC. Plant coverage and soil C/N ratio were the main drivers of C source changes, showing significant positive and negative linear relationships with VSC and MNC content, respectively. Structural equation model showed that plant-derived C is the most important driver of SOC, while microbial-derived C has a significant negative effect on SOC. Conclusions Although both VSC and MNC had a positive response to restoration age, Increasing plant-derived C affected by plant cover and biomass is the main driver of enhanced SOC sequestration in coastal wetlands, compared to microbial-derived C.