Stoichiometry of carbon, nitrogen, and phosphorus in soil: Impacts of soil development and land use across the catchment scale

Abstract

Understanding the evolution and regulation of soil nutrients stoichiometry at different stages of geological development provides critical insights for optimizing fertilization strategies and the sustainable use of land resources. In this study, 1029 soil samples derived from alluvium in the downstream region of the Yangtze River were analyzed, encompassing woodland, dryland and paddy-dryland rotation (paddies). Using the chemical index of alteration (CIA), a relative age sequence of soil development was established, facilitating an investigation into the evolution of soil C:N:P stoichiometry across various stages of parent material development, as well as the factors influencing these changes. As soil matures, organic carbon (OC) and total nitrogen (TN) contents in the surface layer (A horizon) significantly increased by 41.3% and 29.3%, respectively, whereas the content in the deep layer decreased by 51.4% and 9.41%, respectively. Additionally, total phosphorus (TP) content exhibited a marked decline over time in both the A horizon and deep layer. While the C:N ratio of the A horizon and deep layer showed only minor fluctuations, the C:P and N:P ratios in the A horizon significantly increased. Notably, phosphorus limitation, commonly observed in highly developed soils, is absent in this region. At comparable stages of soil development, woodlands and paddies exhibited higher reserves of soil OC and TN compared to adjacent drylands, but they had relatively lower contents of soil TP. These findings suggest that in the downstream region of the Yangtze River, more mature soils exhibited a more balanced ratio of various nutrients. This equilibrium arose from the gradual accumulation of initially deficient OC and TN, alongside a moderate decline in the initially abundant TP. However, for effective soil management, fertilization strategies should account for the contrasting nutrient limitations—namely, OC and TN deficiencies in dryland soils and TP deficiency in paddies.