Characterization of organic matter functional groups and components in soils from a coastal hydrogeomorphic gradient by mid-infrared attenuated total reflectance spectroscopy

Abstract Purpose Coastal vegetated soils play a critical role in global carbon storage and biogeochemical cycling, yet methods for characterising soil organic matter (OM) composition remain limited. This study used mid-infrared attenuated total reflectance (MIR-ATR) in the field for characterization of OM in coastal vegetated sites. Methods The study area comprised three vegetation zones (mangrove, MG; saltmarsh, SM; and paperbark, PB) from Wilsons Promontory National Park, Victoria, Australia. Soil samples (n = 150) were obtained from 10 cores in each zone taken at five 10 cm depth intervals to 50 cm. MG and SM zones are tidally inundated, while PB is supratidal. Multiple curve resolution (MCR) and peak fitting analysis identified organic components and enabled identification of OM functional groups transferred from vegetation to soils. Results Infrared assignments were made according to published tables and reference standards. Organic components of the plant material were dominated by carbohydrates, amide, carboxylate, aromatics lignin and phenolics. MCR revealed similar major organic components for MG and SM but more complexity for PB. Some of the litter organic components, such as cellulose and lipids, were clearly incorporated into the 0-10cm soil layer. Variations in soil OM were strongest in alkyl and carboxylate groups, and there was evidence of additional organic inputs and degradation pathways at intertidal sites. Conclusions It was concluded that the type of vegetation affected the soil chemistry and that MIR-ATR can be used to track changes in soil organic matter under different coastal vegetation types.