Soil available nutrients are key variables for predicting the characteristics of plants, litter, and soil

To clarify how plant, litter, and soil nutrient concentrations and stoichiometric ratios respond to environmental factors and to elucidate the stoichiometric dynamics of the plant-litter-soil continuum and the synergistic relationships among its components, we focused on Pinus densata forests typical of southeastern Xizang. We measured climatic variables at 3,100, 3,400, and 3,700 m, together with carbon (C), nitrogen (N), and phosphorus (P) concentrations in plant (leaf, branch, trunk, root), litter (undecomposed layer, partially decomposed layer, fully decomposed layer), and soil (0-10 cm, 10-20 cm, 20-40 cm), as well as soil physicochemical properties. The results showed that, across elevations, plants, litter, and soils differed significantly in C, N, and P concentrations and in their stoichiometric ratios. At a given elevation, the C and P concentrations followed the order plants > litter > soil. Within plants, leaves had significantly higher C, N, and P concentrations than branches, trunks, and roots. In litter, C concentration and the C:N and C:P ratios were highest in the undecomposed layer, whereas N and P concentrations were highest in the partially decomposed layer. Soil available nitrogen (AN), available phosphorus (AP), and C, N, and P concentrations, as well as stoichiometric ratios, were highest in the 0–10 cm layer and declined with increasing depth. Using redundancy analysis (RDA) and partial least squares path modeling (PLS-PM), we detected significant interactions among plant, litter, and soil nutrients; The impacts of environmental factors on stoichiometry differed among these compartments and soil AN and AP were key predictors of variation in C:N:P stoichiometry across plant, litter, and soil. Plant growth in the study area was limited by N. Collectively, these findings provide new perspectives and references for elucidating, under global climate change, aboveground and belowground nutrient cycling, nutrient limitation, and plant–environment relationships in montane P. densata forests.