The Impact of Nitrogen Addition on Soil Carbon Components and Understory Vegetation in Moso Bamboo Forests

Moso bamboo forests are ecologically and economically important in China, but the effects of nitrogen addition on soil carbon dynamics and vegetation are underexplored. This study applied six nitrogen treatment levels in a monoculture Moso bamboo forest, collecting soil samples from 0 to 30 cm depth and understory vegetation data. The results showed that nitrogen addition significantly reduced stable carbon components, while particulate organic carbon (POC) increased, suggesting that excessive nitrogen may destabilize the soil carbon pool by accelerating SOC decomposition or reducing accumulation. Vertical variations in soil carbon components were more significant in the 20-30 cm layer, indicating stronger impacts on deep SOC cycling. Nitrogen reshaped the community structure, notably affecting dominant species such as Viola davidii and Rubus buergeri. However, species diversity indices showed no significant changes, likely due to the vegetation's high adaptability to nitrogen. Correlation analysis indicated that stable carbon components positively influenced vegetation diversity, while POC had a negative effect. Partial least squares path modeling (PLS-PM) explained 95.12% of the variance in the relationship between nitrogen, soil carbon components, and vegetation diversity. Nitrogen negatively affected soil carbon components but positively influenced vegetation diversity, while soil carbon components negatively impacted diversity. Nitrogen may promote certain carbon component accumulation but could weaken the forest's carbon sink function.