Effects of grazing and mowing on vertical distribution of soil nutrients and their stoichiometry (C: N: P) in a semi-arid grassland of North China

Abstract

Grazing and mowing are increasingly recognized as a major driver of variations in soil nutrient levels during grassland management process. However, relatively few studies have examined the effects of grazing and mowing on the variations in concentrations, stocks, and stoichiometry of soil organic carbon (SOC), total nitrogen (TN), and total phosphorous (TP) in the deepsoil layer. In this study, a 6-year trial was conducted under grazing and mowing in a semi-arid grassland of North China to compare the concentrations, stocks, and stoichiometry of SOC, TN and TP in the top 1 m soil layer. The results indicated that both grazing and mowing increased SOC and TN stocks in the topsoil layer (0–30 cm), while mowing decreased SOC stock in the subsoil layer (30–100 cm). Meanwhile, neither treatment had any significant effects on TP concentrations and stock in the entire 0–100 cm profile. However, both grazing and mowing caused a decline in C:N and C:P ratios at 50–70 cm depth. The shifts in plant community composition regulated the changes of SOC and TN stocks in the topsoil layer, while resource allocation between aboveground plants and belowground roots regulated the changes of SOC stock and C:N:P stoichiometry in the subsoil layer. It is speculated that low-frequency grazing might be a sustainable grassland management regime, as it conserves both above- and belowground parts and maintains healthy ecosystem functions in semi-arid grasslands.