Patterns and driving mechanism of soil organic carbon, nitrogen, and phosphorus stoichiometry across northern China's desert-grassland transition zone

Abstract

Desert-grassland transition zone is a critical ecological barrier frontier against sandstorms and desertification in northern China. Soil nutrient stoichiometry is closely related to plant community biomass, biodiversity, ecosystem functions and stability. However, how the relationship between climate, vegetation, and soil property drives the spatial pattern of soil nutrient stoichiometry remains unclear. We investigated soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents and their ratios (C:N, C:P and N:P) from 82 sites located in a desert-grassland transition zone in Inner Mongolia. SOC, TN, and TP contents, and soil C:P and N:P ratios were higher in typical grassland than that in shrub desert, higher in aridisols than in desert soil and desert eolian sand soil. The C:N ratio showed no significant difference between different vegetation types. SOC and TN contents showed an apparent decrease with soil depth in aridisols, of which the surface was well-covered by herbaceous plants. Soil TP content, C:N, C:P, and N:P ratios are different primarily among soil types, but not along soil depth, which may be mainly attributed to SOC, TN, and TP changed synergistically and weak soil leaching in desert areas. Redundancy analysis showed that precipitation, and silt and clay content were the most critical factors influencing SOC, TN, and TP stoichiometry. Structural equation modeling revealed that precipitation could impact soil nutrient stoichiometry by affecting the vegetation and soil physicochemical properties. Temperature and soil pH had impact on the mineralization and decomposition of organic matters, and significant direct and negative effect on SOC, TN, C:P, and N:P (except MAT) ratio. Our results highlighted the importance of current climate change on soil organic C, TN, and TP contents and C:N:P stoichiometry, and future climate change and its eco-impact in the desert-grassland transition zone.