Runoff velocity controls soil nitrogen leaching in subtropical restored forest in southern China

Nitrogen (N) leaching is a complex process regulating N exchange between the soil and aquatic ecosystems and may result in groundwater pollution, threatening ecosystem security. However, the mechanisms driving N leaching in subtropical forests have not been fully elucidated. Here, we present a quantitative analysis of vegetation-soil relationships in response to N leaching in a subtropical forest located in southern China. The results reveal that N leaching in runoff at lower simulated precipitation intensities (60 mm/h, 90 mm/h) and in sediment generated under higher intensities (120 mm/h, 150 mm/h) were significantly different across five vegetation restoration types. NH4+-N and TN were mostly lost through sedimentation, whereas NO3--N was primarily leached in runoff (80%-88%). N leaching was positively correlated with runoff, sedimentation rate, geometric mean diameter, mean weight diameter, and fine sediment particles (<0.25 mm), but negatively correlated with fractal dimension and coarser sediment particles. Random forest analysis demonstrated that runoff velocity was a critical driver of N leaching, suggesting that the impact of plant restoration on N loss should be considered. In order to minimize N leaching and resultant water pollution, guidelines informing the design of vegetation restoration projects in subtropical monsoon forests should emphasize the importance of planting Pinus elliottii. This result emphasized the importance of leaching erosion in forest ecosystem management and the need to understand the intricacies in the soil nitrogen sequestration potential at a regional scale in a changing climate.

Automated summary

A quantitative analysis of vegetation-soil relationships in a subtropical forest in southern China revealed significant differences in nitrogen (N) leaching across different vegetation types, with Pinus elliottii identified as an important plant for reducing N leaching and water pollution.