Depth-Dependence of Soil Stoichiometry Decoupling in China’s Croplands over the Last Four Decades

Soil carbon (C), nitrogen (N) and phosphorus (P) stoichiometry is an integrative metric for the balance and restrictive relationships of 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, we assess variations in soil C:N:P ratios across a 0-100 cm soil profile in China’s croplands by conducting repeated soil C, N, and P measurements at 305 resampling sites in 1980s and 2023, totaling 6,405 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. Our results highlight the depth-dependent decoupling of soil stoichiometry in response to long-term management practices and its implications for ecosystem services.