The response of plant-derived lignin phenols accumulation to nutrient addition depends on soil depth in a subtropical plantation

Aims

Plant-derived stable carbon is the main contributor to soil organic carbon (SOC) in forest ecosystems. However, the accumulation of plant-derived lignin phenols in the soil profile in response to nitrogen (N) and phosphorus (P) addition, as well as their driving mechanisms, remains unclear.

Methods

The topsoil (0-20cm) and subsoil (50-70cm) were collected and divided into particulate (PF) and mineral-associated fractions (MF) after 9 years of N and P additions in a subtropical plantation. SOC functional groups, lignin phenols, fungal ITS gene abundance, community structure and function were investigated.

Results

The SOC-normalized lignin phenols (NLP) decreased in bulk soil (BS) and PF of topsoil, while increased in BS and MF of subsoil after P addition, suggesting P addition enhances the contribution of lignin to SOC in the subsoil but decreases it in the topsoil. P addition increased lignin degradation degree (LDD) in the topsoil but decreased it in the subsoil. Nutrient addition unaffected fungal community diversity, but Basidiomycetes and Mortierellomycota abundance in the topsoil increased after P addition. The NLP was negatively correlated with Basidiomycetes abundance in the topsoil and was positively correlated with the LDD in the subsoil, indicating that the accumulation of lignin is primarily governed by the microbial community composition in the topsoil, whereas it is dependent on the lignin molecular composition in the subsoil.

Conclusion

Our results suggest that nutrient addition will have different impacts on carbon sequestration in the soil profile by altering the accumulation of plant-derived lignin phenols through distinct mechanisms in plantation forests.