Understanding Changes In Litter Carbon Chemistry Caused by Decomposition Using Advanced Solid-State NMR Spectroscopy.

The information on the litter decomposition is critical to the understanding of the net C balance of a site. However, how litter chemistry controls litter decomposition is still not very clear. In this study, we employed advanced ¹³C solid-state NMR techniques to study the chemical structural changes during litter decomposition. These techniques included cross polarization/total sideband suppression, chemical shift anisotropy filter, dipolar dephasing, ¹H-¹³C recoupled long-range dipolar dephasing, and direct polarization/magic angle spinning. The samples used were litters (both non-decomposed and highly decomposed) from four wood species (Acer saccharum (ACSA), Drypetes glauca (DRGL), Pinus resinosa (PIRE), and Thuja plicata (THPL)) at four sites with different annual mean temperatures, collected from Long-term Intersite Experiment. The results indicated that (1) alkyl group, OCH₃/NCH, carboxylic groups increased whereas carbohydrates decreased during decomposition; and (2) the decomposition degree of four species at same site followed the decreasing order of DRGL > PIRE > THPL > ACSA. Advanced solid-state NMR techniques provided deep insight into the chemical structural changes during litter decomposition.