Effects of nitrogen addition on soil organic carbon and its fractions in China’s terrestrial ecosystems

Objective As a key component of the global carbon cycle, China’s terrestrial ecosystems play a crucial role in maintaining regional carbon balance through their carbon sink function. However, the responses and mechanisms of soil organic carbon (SOC) and its fractions to nitrogen (N) deposition remain poorly understood.

Method This study integrated 38 nitrogen addition experiments from China’s terrestrial ecosystems, comprising 141 observations of particulate organic carbon (POC) and 99 observations of mineral-associated organic carbon (MAOC), to systematically analyze the effects of N addition on SOC and its fractions.

Result Nitrogen addition significantly increased SOC by 5.18% and POM by 12.91%, but had no significant effect on MAOC. This differential response primarily resulted from the distinct formation mechanisms and stability between POC and MAOC. Further analysis indicated that the positive effect of N addition on SOC was more pronounced under conditions of forest ecosystems, high N addition rates (> 100 kg/(hm²·a)), inorganic N fertilization, and short-term fertilization (< 5 years). While the effect on POM was more pronounced in agroecosystems, high N addition rates (> 100 kg/(hm²·a)), organic N fertilization, and short-term fertilization (< 5 years). Notably, MAOC showed no significant change under all treatment conditions.

Conclusion This study reveals that N addition promotes SOC accumulation in China’s terrestrial ecosystems and alters the functional components of SOC. The findings suggest that assessing the impact of N addition on SOC requires a comprehensive consideration of ecosystem types, soil quality, and N management strategies. Our results provide new insights into the impact of N deposition on SOC pool and its functions in China’s terrestrial ecosystems, contributing to a more accurate prediction of SOC dynamics and feedbacks to future atmospheric nitrogen deposition, as well as offering data support for the development of differentiated carbon sequestration and emission reduction strategies.