Asymmetric responses of plant aboveground and belowground stoichiometry to precipitation in Tibetan alpine grasslands

Precipitation is a key climatic driver regulating plant nutrient stoichiometry, with significant implications for ecosystem function. However, the differential responses of aboveground and belowground plant components to precipitation variability remain poorly understood, especially in alpine ecosystems. We investigated carbon (C), nitrogen (N), and phosphorus (P) stoichiometry in plants and soils across a 1500-km precipitation gradient on the Tibetan Plateau. C, N, and P concentrations in both aboveground biomass (389.39 g kg⁻¹, 15.32 g kg⁻¹, 1.22 g kg⁻¹) and soil nutrients (8.12 g kg⁻¹, 0.94 g kg⁻¹, 0.39 g kg⁻¹) were lower than in Mongolia Plateau grasslands, indicating nutrient limitation in cold, arid conditions. Precipitation had a dominant influence on stoichiometric patterns, with aboveground and belowground tissues showing opposing responses. C concentrations, and C:N and C:P ratios in aboveground biomass decreased with precipitation, while those in belowground biomass increased. N and P concentrations were consistently higher in aboveground tissues, reflecting stronger homeostatic control. Soil C and N increased with precipitation, while soil P declined, indicating P limitation. Plant C:N and N:P ratios were negatively and positively correlated with soil stoichiometry, respectively, suggesting organ-specific nutrient regulation. These findings highlight asymmetric stoichiometric responses between plant compartments and the role of belowground nutrient dynamics in plant adaptation to changing precipitation regimes. Our study emphasizes the importance of belowground traits in ecosystem nutrient cycling under climate change.