Rhizosphere priming mechanisms on soil organic carbon decomposition differ among exudate components and are regulated by mycorrhizal type: Insights from a temperate forest in northeast China

Root exudate-derived labile carbon (C) inputs can lead to a strong short-term change in microbial mineralization of rhizosphere soil organic carbon (SOC), which is termed the rhizosphere priming effect (RPE). In this study, we added three exudate components surrogates (glucose, oxalic acid, and glycine) to rhizosphere soils collected from eight tree species, exploring how tree species variation modulated the response of RPE to addition of root exudate components. Our results showed that adding glucose and glycine enhanced soil C mineralization through biotic mechanisms, while adding oxalic acid enhanced soil C mineralization through abiotic mechanisms. Compared with control, adding glucose, oxalic acid, and glycine additions increased cumulative C mineralization by 94.1 %, 87.6 %, and 26.8 %, respectively (eight species combined). Moreover, the increase in rhizosphere cumulative C mineralization induced by adding glucose and oxalic acid was greater in arbuscular mycorrhizal (AM) soils (5.33 and 5.12 mg CO₂-C g⁻¹ soil) than in ectomycorrhizal (ECM) soils (4.82 and 4.69 mg CO₂-C g⁻¹ soil). However, the relationships among enzyme activity, microbial biomass, and C mineralization depended on tree species, and different tree species have an inconsistent biotic driving mechanism for RPE. There was no linear relationship between cumulative C mineralization and bioavailable C and N among soils. Instead, soil/microbial C:N imbalances and easily oxidizable carbon (EOC) content were crucial factors regulating RPE among temperate forest tree species. Taken together, the effect of root exudates on soil C mineralization was component-specific, and RPE was driven by both root exudate components and mycorrhizal types.