Environmental and Botanical Controls on Peatification - a Comparative Study of Two New Zealand Restiad Bogs using Py-GC/MS, Petrography and Fungal Analysis
Abstract
This study shows that chemical properties of two restiad species, Empodisma minus and Sporadanthus traversii, may contribute to their success as peat-formers in a climate of the North Island of New Zealand which is not conducive to raised mire development. Unlike Sphagnum, the equivalent northern hemisphere peat-former, restiads possess lignin in their tissues. In addition, the presence of non-lignin polyphenols (including tannins and phenolic acids) in restiads may be an important factor in peat formation due to the allelopathic decay retardation. Patterns of degradation of plant biopolymers have been examined and the pathway of degradation of monocotyledons (loss of non-lignin phenolic fraction, depolymerization via modification of side chains of β-O-4 lignin, depletion of hemicelluloses) was identified. Trends in chemical change for lignin were not necessarily paralleled by a similar change in the degree of plant structure preservation - an expression of a complex nature of degradation involving the contributions of several processes affecting different classes of biopolymers to different extents. A further finding of this study is that the degree of lignin breakdown, together with proportions of fungal hyphae and petrogrpahic character, indicate that one of the two bogs studied, Moanatuatua, has undergone far more aerobic decay throughout its development than has its climatic and vegetational equivalent, Lopouatai. This is thought to be due to differing water tables in the two sedimentary environments. Moanatuatua developed in a flood plain distant from the sea with a migrating river system, while Kopouatai developed near the sea. A high degree of natural peat decomposition at Moanatuatua most probably precluded any further rapid decay after recent agricultural drainage.