Specific features of the structure of oligotrophic peatlands in the Arctic ecoregions

The ecological functions of bog ecosystems and their resistance to external influences are largely determined by the structure and chemical composition of peat.

The structure of thick peat deposits of oligotrophic bogs typical for the west of the Arctic ecoregion of Russia is studied.  The investigated peatlands are affected by the seas of the Arctic Ocean (the White and Barents).  Bog massifs in the continental climate zone without marine influence outside the Arctic territories were studied for comparison purposes. The studied bog natural complexes all belong to the oligotrophic type, are similar in structure to the deposit profile, have a peat layer of the comparable thickness and a similar homogeneous botanical composition. The peat of all studied bogs is characterized by a low degree of decomposition over the entire depth of the profile (not more than 15-20%).

The degree of decomposition, the botanical composition and the structure of the samples was studied by transmitted-light-microscopy. Fractionation was carried out by elutriation on sieves with a mesh size of 100 μm and 250 μm.

The macrostructure of the studied peat bogs is formed by the undecomposed and weakly decomposed residues of peat-forming plants - mainly sphagnum mosses mixed with cotton-grass in certain layers. Analysis of peat samples from the Arctic ecoregion showed a high degree of grinding of sphagnum moss residues without visible signs of biochemical disturbance of cellular structures. This feature is most noticeable when considering the fraction of 100-250 μm, where particles of such plant residues are concentrated. Leaves of sphagnum mosses in peat samples from the Arctic maritime territories are broken, but the cellular structures retain their integrity. In peat samples from bogs of the continental climatic zone, this phenomenon is not observed. Plant residues retain their integrity quite well, both in the upper and lower layers, and the fraction of 100-250 μm is composed of undisturbed leaves of sphagnum mosses.

The revealed specific nature of defragmentation of plant residues in the conditions of oligotrophic bog massifs of the Arctic ecoregion can be explained by the freezing-thawing cycles during the formation of a stable snow cover. In the conditions of a maritime subarctic climate, a stable snow cover is formed for a long period in the multiple transitions of air and soil temperatures through the zero-temperature mark. The thickness of the snow cover under the influence of winds in the open spaces of the bogs can decrease to the minimum values. The noted structural features are traced throughout the depth of the deposit. However, increased content of physically destroyed particles of sphagnum mosses in the upper horizons of the peat deposit in the maritime subarctic climate is observed, which may well be associated with global warming and an increase in freezing-thawing cycles.

The obtained results require confirmation in the framework of model experiments both in the conditions of a mesocosm and laboratory. Besides, the extensive comparative studies on similar peat deposits in a maritime and continental climate must be made.