Depth-Dependence Changes in Soil Stoichiometry in China's Croplands Over the Past Four Decades.

Soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry is an integrative metric that reflects the balance and limiting relationships among soil elements. However, how climate change and nutrient inputs affect cropland C:N:P ratios along soil profiles at large scales remains largely unknown. Here, variations in soil C:N:P ratios across a 0-100 cm soil profile in China's croplands is assessed, based on repeated measurements at 305 resampling sites in the 1980s and 2023, totaling 6405 soil profiles. Over the past four decades, the mean soil C:N ratio across the entire profile increases by 20.18%, the C:P ratio increases by 4.49%, while the N:P ratio decreases by 9.02%. Spatially, changes in C:N and N:P ratios tend to weaken with increasing latitude. These changes exhibit clear depth-dependent patterns. The soil C:N ratios increase across the entire soil profile, while the C:P and N:P ratios increase in the topsoil (0-40 cm) but decrease in the subsoil (40-100 cm), primarily driven by organic C and nutrient inputs, influenced by initial soil conditions and climate. The results highlight the depth-dependent changes in soil stoichiometry in response to long-term management practices and their implications for ecosystem services.