| Sub-fossil and recent plants from bogs in Canada, New Zealand and Poland were analyzed by pyrolysis-gas chromatography/mass spectrometry and their structural biopolymers were characterized. A technique of on-line sequential pyrolysis was developed to study some of the plant tissues. The sequential pyrolysis allowed a more precise characterization of the sample, by accounting for thermal stability of distinct biopolymers. Studies of the relationship between bog hydrology and biodegradation permitted the development of a chemical proxy for bog paleohydrology, based on the extent of lignin enzymatic oxidation. Lignin oxidation was measured to reconstruct past peat surface wetness (PSW) of several bogs. The chemical records were generally in agreement with botanical stratigraphy. Analysis of individual macrofossils rather than bulk organic matter (OM) allowed detection of diagenetic features otherwise not apparent. Differences attributable to tissue chemistry and to the method of litter deposition have been observed. Typically only roots or subaerial organs rich in lignin, cutin etc. were preserved. On the other hand, Sphagnum appeared to be very resistant. Most degradation occurred in the upper, oxic section of the bog. Zonation of diagenetic effects corresponded to the availability of oxygen. Anaerobic degradation of vascular plant polysaccharides was noticeable only into the upper catotelm (anoxic peat layer). In the lower catotelm, the vascular OM was apparently inert. Sphagnum was degraded more slowly than vascular plants, but no cessation of degradation was observed. Elevated degradation of samples collected from the several centimeter layer directly above the contact with mineral soil was observed, possibly an effect of oxidants supply with groundwater. Effects of an environmental change on anaerobic carbon dynamics potentially would be largest if the hydrology was disturbed at a wet and vascular plant-rich site. Peat deposited under a dry regime would be relatively inert under anaerobic conditions. Although catotelmic degradation usually is not extensive, in some cases, if acrotelmic degradation is minor and labile OM is retained (e.g., a restiad bog from New Zealand), a major fraction of peat is degraded in the catotelm, potentially resulting in a significant export of 14C-old CH4. |
