Anatomy of recent and peatified Calluna vulgaris stems: implications for coal maceral formation

Abstract

Anatomical characteristics of peatified Calluna vulgaris stems isolated from a selection of Northwest European raised bog peat deposits were compared with intact stems in order to reveal anatomical modifications caused by the peatification process. Four main decomposition processes were discerned: ( 1 ) loss of structural integrity of cell walls and cell inclusions; (2) gelification and swelling of cell walls; (3) discolouration of cell walls; and (4) deposition of matter in cell lumina.Fibre-tracheids and wood parenchyma appear to be the most affected cell types. The two main decomposition trends discerned in these tissues were related to different fungal types. Precipitation of decay products was mainly observed in vessels. Bark tissues, primary xylem and medullary parenchyma were characterized by an excellent anatomical preservation. In the first stages of peatification a rapid decrease in cell contents was observed in bark tissues. Swelling and gelification was mainly seen in cell walls of the cambium and vessels.We conclude that different types of cell walls respond differently to decay conditions. This is probably related to differences in the original cell wall chemistry. A high intra-and intercellular variability in degree of preservation was sometimes observed in identical tissues. The microscopic variability arising during peatification of wood and bark testifies to the heterogeneity of coal macerals derived from these tissues.

Consequences of drying on the hydro-mechanical response of fibrous peats upon compression

“…Peat is formed in wet conditions, and waterlogged peat deposits are poor in oxygen, which together with low temperatures inhibits the growth of aerobic fungi and bacteria and delays the biodegradation of plant remains (Wardwell et al 1983;Van der Heijden et al 1994). However, the frequency and the severity of droughts are expected to increase dramatically in the near future (IPCC 2007;KNMI 2014), which will increase the susceptibility of peats to degradation.…”