The hidden role of glomalin-related soil protein in mediating soil organic carbon dynamics in response to urbanization

Abstract

Abstract Urbanization can alter soil organic carbon (SOC) storage, while glomalin-related soil protein (GRSP) is crucial for SOC sequestration. However, whether and how GRSP mediates the response of SOC to urbanization remains unclear. We investigated 184 soil samples by analyzing GRSP and its C-functional structures along an urban expansion gradient using redundancy analysis and structural equation modeling (SEM) in Nanchang, China. Four C-functional groups of GRSP were characterized using infrared spectroscopy, including aromatic hydrocarbons, aliphatic hydrocarbons, proteins, and polysaccharides/nucleic acids. Average GRSP and SOC contents were 2.38 and 16.76 g·kg⁻¹, respectively, and both decreased significantly during urbanization ( p  < 0.05). Crucially, the relative abundance of the fourC-functional groups of GRSP exhibited a more pronounced decline with urbanization than that of bulk soil C-functional groups, providing a mechanistic basis for its sensitivity. SEM indicated that GRSP was significantly associated with the pathway linking urbanization and SOC, suggesting that urbanization may be indirectly associated with SOC variation through changes in soil properties (e.g., enzyme activities) and GRSP. This study suggests that GRSP content and its C-functional structure may serve as potential biochemical indicators of urbanization-associated changes in SOC dynamics. It provides a biochemical tool for assessing soil carbon vulnerability in urban ecosystems.