Developing an understanding of the response of soil organic carbon (SOC) to N deposition is critical to quantify and predict the terrestrial carbon uptake under increasing N deposition in the future. However, results from field studies on the response of SOC content and composition to N deposition are highly variable across different ecosystems. The interpretation of SOC responses to N deposition are often complicated by the differences in climate, soil substrate and other factors.

To address this question, the Ph.D. student YU Mengxiao, under the joint guidance of Prof. YAN Junhua and WANG Yingping, conducted research on SOC and its components in adjacent broadleaved and coniferous subtropical forests after 14 years of N addition. They found SOC significantly increased with N addition in the broadleaved forest (old forest), but did not change significantly in the coniferous forest (young forest).

Increased SOC in the broadleaved forest was mostly contributed by the significant increases in humus organic carbon (HOC) and resistant organic carbon (ROC). The increased SOC accumulation in the broadleaved forest was largely driven by altered rates of organic matter decomposition, rather than C inputs to soil. Land-history and low nutrient availability may have contributed to the lack of significant impact of N deposition on SOC in the coniferous forest. These results suggested the different response and regulate mechanism of SOC with N deposition in subtropical forests. This study verified that N deposition increase soil carbon sequestration under global change in subtropical forest.

The research results entitle by "Divergent responses of soil organic carbon accumulation to 14 years of nitrogen addition in two typical subtropical forests" was published in the Science of the Total Environment. For further reading, please refer to: https://doi.org/10.1016/j.scitotenv.2019.136104.

Figure. A conceptual scheme depicting the mechanisms that explain the different response of SOC to N addition in the broadleaved forest