The Role of Leaching in Soil Carbon, Nitrogen, and Phosphorus Distributions in Subalpine Coniferous Forests on Gongga Mountain, Southwest China

Abstract

To explore the role of leaching in mountainous nutrient cycling, we investigated the altitudinal distribution of soil carbon (C), nitrogen (N), and phosphorus (P) in the subalpine coniferous forest ranging from 2628 to 3044 m on the eastern slope of Mt. Gongga. The results revealed that concentrations of C and N, as well as the atomic ratios of C:N and N:P, showed no significant difference among the sampling sites (p > 0.05) in O horizons. The concentrations of P in O horizons increased gradually with altitude. In contrast, notable variations in C, N, and P concentrations and stoichiometry were observed in the mineral horizons. Lower concentrations of C, N, and P were found in A horizons, while higher contents were present in B and C horizons compared to previous studies. Additionally, results of the random forest model indicated that C and N concentrations in the O, B, and C horizons, as well as P concentration in the B horizons, were primarily influenced by Feox concentrations. This suggested that these nutrients leached from O horizons and accumulated in B and C horizons alongside Feox. Except for C:N ratios in the O horizon, the C:N, C:P, and N:P ratios in the O, B, and C horizons were mainly affected by concentrations of Feox or Alox. These results underscored the substantial impact of leaching processes on the spatial distribution of soil C, N, and P, ultimately leading to changes in the gradient distribution of soil C:N:P stoichiometry. Specifically, the C:N ratio in the mineral horizons at the 2781 m site was significantly higher compared to other sites (p < 0.05), indicating a greater movement of C relative to N. The C:P and N:P ratios in the B horizon at the 2781 m site were notably higher than at other sampling sites (p < 0.05). Conversely, the N:P ratio in the A horizon at the 2781 m site was relatively low. Furthermore, concentrations of C and N in the B horizon at the 2781 m site were significantly higher than in other sampling points, while P concentrations were notably lower (p < 0.05). This suggested a more pronounced downward leaching of C and N compared to P at the 2781 site, indicating stronger leaching effects. Overall, this study emphasizes the significant influence of leaching processes on the spatial distributions of soil C, N, and P in subalpine coniferous forests in Southwest China.