Successional Shifts in Soil C:N:P stoichiometry and its environmental controls during forest restoration in Huize County, Qujing, Yunnan Province

Abstract

Forest restoration reshapes nutrient cycling and soil stoichiometric regulation in fragile plateau ecosystems. To clarify variations in soil C:N:P stoichiometry and its environmental controls during ecosystem recovery on the southwestern China plateau, this study investigated three representative forest types along a restoration gradient, including Pinus yunnanensis forest, mixed conifer broadleaf forest, and secondary evergreen broadleaved forest. Soil samples were collected from three depths of 0–20 cm, 20–50 cm, and 50–80 cm, together with dominant tree leaf samples, and a total of 27 composite soil samples and 81 undisturbed soil cores were analyzed. Heatmap analysis, Mantel tests, redundancy analysis, and random forest modeling were used to evaluate stoichiometric characteristics and regulatory mechanisms. The results showed that soil organic carbon or total organic carbon and total nitrogen were the dominant factors controlling soil stoichiometry across forest types, whereas the effects of soil layer, iron and aluminum oxides, pH, and nutrient fractions varied with restoration stage. In the Pinus yunnanensis forest, available K and available Al were the primary predictors of C:P, and total nitrogen was the primary predictor of N:P. In the mixed conifer broadleaf forest, total organic carbon became the primary predictor of C:P and C:N ratios, while nitrogen fractions strongly regulated N:P variation. In the evergreen broadleaved forest, C:P was co-regulated by total P, available Al, TOC, and nitrate nitrogen, while N:P was predominantly governed by total P and total N. The explanatory power of environmental variables increased markedly along the restoration gradient, and nutrient heterogeneity in the 0–20 cm soil layer intensified during later restoration stages.Mixed‑effects models confirmed that forest type × depth interactions significantly modulated Al, Fe, and P stoichiometry, corroborating the successional shift from physical to biogeochemical controls. These results indicate that forest restoration progressively strengthens plant-soil nutrient associations and corresponds to a transition from available K/Al and bulk density constraints in the early-stage plantation toward absolute nutrient pools and organo-mineral interactions in the mature forest.