Abstract
This study examined the chemical composition of soil organic matter (SOM) along a 2,000-year paddy soil chronosequence in eastern China by use of advanced solid-state nuclear magnetic resonance (NMR) spectroscopy as well as Fourier transform infrared spectroscopy (FTIR), aiming to identify changes in the chemical composition of SOM over a millennium timescale. The results showed that soil organic carbon concentration in the surface soil reached a steady state after 100 years of rice (Oryza sativa L.)–wheat (Triticum sp.) cropping on coastal tidal flats. The¹³C NMR spectra and fractions of structural groups or components of the whole SOM samples differed little along the chronosequence, suggesting a similar chemical composition in SOM samples regardless of the duration of rice cultivation. The FTIR spectral pattern and relative intensities of some resolved functional groups or components of whole SOM were also similar along the soil chronosequence. The similarities in chemical composition of SOM can be attributed to the rice–wheat cropping system, in which SOM has undergone ongoing turnover under periodical fresh plant material input and wet–dry cropping alternation, leading to a similar chemical composition of bulk SOM.