Changes in organic components for fallen logs in old-growth Douglas-fir forests monitored by 13C nuclear magnetic resonance spectroscopy

13C cross-polarization magic-angle spinning nuclear magnetic resonance (CPMAS NMR) spectroscopy was used to characterize heartwood from decaying fallen boles of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), western hemlock (Tsugaheterophylla (Raf.) Sarg.), and western red cedar (Thujaplicata Donn). The sample decay classes I to V had been previously assigned based on field observations. Solid-state 13C CPMAS NMR spectra were analyzed to determine the proportion of C of the following chemical types: carbohydrate, lignin, aliphatic, and the sum of carboxyl plus carbonyl. For both Douglas-fir and western hemlock, the proportion of carbohydrate C increased slightly in the early stages of decay. This was followed by a substantial increase in lignin C, while carbohydrate C declined to about 10% of total C. By contrast, the spectra for western red cedar generally showed little change with increasing decay class. One exceptional sample of western red cedar class IV was highly decomposed, indicating complete loss of carbohydrate C, and some loss of lignin side-chain C. For all three species, signals from alkyl and carbonyl C were weak, but tended to increase slightly with decomposition, most likely because of the selective preservation of waxes and resins (alkyl C), and oxidation. Accumulation of chitin was not observed, and there was little evidence for lignin decomposition or for formation of humic polymers. 13C CPMAS NMR offers a simple and information-rich alternative to wet chemical analyses to monitor changes in organic components during decomposition of woody litter.