Driving mechanisms of functional groups in soil particulate organic matter in different Suaeda salsa habitats of the Yellow River Delta

Abstract

Plant stoichiometry significantly influences the accumulation and stability of soil particulate organic matter (POM). This study analyzed soil profiles (0–30 cm depth) of Suaeda salsa communities in the intertidal habitat (Habitat I) and supratidal habitat (Habitat II) of the Yellow River Delta. Fourier transform infrared spectroscopy (FT-IR) combined with two-dimensional correlation spectroscopy (2D-COS) was employed to characterize POM functional group structures and identify their dynamic response characteristics under habitat perturbation. Plant C:N:P stoichiometry and soil physicochemical factors were integrated to elucidate the driving mechanisms of POM. Key findings include: (1) POM functional group composition differed significantly between habitats but showed minimal variation with soil depth. POM in Habitat I was dominated by hydrophilic groups, while POM in Habitat II was characterized by hydrophobic groups. (2) The 2D-COS analysis revealed that polysaccharide-associated C–O groups exhibited earlier spectral responses to habitat perturbation than aromatic CC and N–H groups, indicating higher environmental sensitivity of hydrophilic components. The response intensity of functional groups gradually weakened with increasing soil depth, suggesting enhanced microstructural stability of deeper POM fractions. (3) Plant stoichiometry significantly influenced POM functional group composition. In Habitat II, higher foliar C and a lower leaf C:N promoted the enrichment of aromatic functional groups, contributing to relatively greater chemical recalcitrance of POM. Environmental factors also critically affected POM composition. Higher salinity and periodic tidal inundation in Habitat I favored POM accumulation despite the predominance of hydrophilic functional groups. This study reveals that stoichiometric regulation by plants modulates the composition mechanisms of POM functional groups across habitats, offering critical insights for wetland carbon cycling and carbon sequestration.