We used solid-state carbon-13 nuclear magnetic resonance (NMR) to compare chemical compositions of
carbon in plant litter, forest floor and soil in a native seasonal rain forest (SR) with those in a rubber
plantation (RP) in Xishuangbanna, southwest China. We also applied a sequential fumigationeincubation
(SFI) procedure to characterize the chemical compositional change of soil organic carbon (SOC) during soil
degradation. It was found that RP had 1.5e1.7 times greater in alkyl C0e45ppm proportions and smaller
O-alkyls C45110 fractions in litter and forest floor materials than SR. Degradation of labile organic carbon
(LOC) in fresh litter was primarily limited to O-alkyl C and O2-alkyl C in both forests, suggesting litters of RP
were less decomposable than that of SR. SOC in RP was 2.3 percent higher in aromatics C110e160ppm
proportions and 0.03 percent in aromaticity value than those in SR. With the absence of new C input
and fauna, degradation of soil LOC companied with loss of carbonyls C160220ppm in RP, and alkyl C and
aromatics C110e160ppm in SR. Our data indicated that rubber planting induced carbon loss and extensive
humification in the soil. Sources of the decomposed soil LOC can compose of both simple and complex
chemical compounds.