Urbanization led to a decline in glomalin-soil-carbon sequestration and responsible factors examination in Changchun, Northeastern China

Glomalin-related soil protein (GRSP) is a proxy for soil arbuscular mycorrhizal fungi (AMF) and is crucial for soil organic carbon (SOC) storage. Urbanization has been recognized one of the main human disturbance to nature, and its influence on GRSP and SOC sequestration is important by reporting from previous studies. In the current study, at the first time, impervious surface area (ISA) was used as urbanization indicator, we tried to find urbanization effects on glomalin traits (total GRSP (TG), easily-extracted GRSP (EEG), TG/SOC, EEG/TG, and EEG/SOC) in Changchun city. Total 281 plots were sampled in the 500-km(2) urban region. Twenty-four parameters were recorded as forest characteristics (plant diversity traits, tree size, and tree density), soil properties (pH, bulk density, electrical conductivity (EC), and temperature), and land use configuration (road, greenspace, building, and water). We found that GRSP contributed 1.3-1.6 times SOC sequestration in low-medium urbanization areas (ISA <= 0.8) than in heavy urbanization areas (ISA > 0.8). Association decoupling manifested that, in low-medium urbanization areas, soil properties (including pH, bulk density, EC, and temperature) explained 48-78 % of inter-site variation of glomalin traits, while at heavy urbanization areas, the explaining power from forest characteristics enhanced to a percent of 46 %, mainly from Salicaceae (7.8 %), Ulmaceae (5.7 %), and shrub richness (5.3 %) (p < 0.05). Structural equation modeling found that urbanization directly declined EEG/SOC (coefficient: -0.21), and its indirect effect via greenspace configuration (increase building but decrease greenspace) was one-third to half of the direct effect (coefficient: -0.10 for EEG/SOC; -0.07 for TG/SOC). Our findings accurately confirmed that GRSP/SOC decreased from rural to urban center by using ISA as urbanization indicator. Moreover, we highlighted the importance of greenspace configuration in the regulation of underground glomalin-related carbon sequestration during urbanization processes.