Relative contribution of foliar and fine root pine litter to the molecular composition of soil organic matter after in situ degradation

► We compared the fate of 13C/15N labeled ponderosa pine foliar and fine root during 18 months of in situ decomposition. ► We used Curie-point Py-GC-MS-C-IRMS to explore the molecular contribution of litter to soil organic matter composition. ► Initial litter and bulk soil composition differed markedly. ► We found little evidence for selective preservation of plant compounds considered to be recalcitrant. ► Fine roots were preferentially stabilized as microbially derived compounds in stable soil organic matter fraction such as humin.