Vegetation and plant material of the flat palsa peatlands
The aim of the study was to reveal peculiarities and regularities in plant material stock and production as dependent on the plant cover composition, soil characteristics and microrelief of the flat palsa mires in the northern taiga zone in West Siberia. The hollow-lake complexes on permafrost peatlands were chosen as the study sites. The work was carried out in 2013-2017. Plant material structure with differentiation between living and dead belowground organs was investigated and net primary production evaluated. Net primary production was found to range 3.0-4.5 t/ha per year depending on plant species composition of the phytocenosis studied. The production averaged 4.0 t/ha per year with phytomass stock averaging 14.8 t/ha, whereas in dried lake sites the net primary production reached 8.5 t/ha per year with phytomass stock estimated as 18.0 t/ha. On flat palsa sites the ratio of the aboveground shrub production to their belowground production was 1:4, while in hollow sites the belowground organs of sedges and cotton grasses accounted for most of the production, with the ratio of the above- to the belowground production estimated as 1:6. Belowground production share in the total production was found to be maximal (70%) in mesotrophic hollows mainly due to the major sedges and cotton grasses. The total primary production was estimated as4.1 t/ha per year on flat palsa sites, 3.0 t/ha per year in oligotrophic hollows and reached a maximum of 8.5 t/ha per year in dried lake sites. Thus the average plant material stocks, both above- and belowground, seemed to be rather constant from year to year, and their estimates agreed well with those reported for mires in Canada, Sweden and Finland. Phytomass stocks and production in flat palsa mires in the northern taiga of the West Siberia were shown to depend on soil mineral nutrition and water availability in the root-inhabited layer. Only in oligotrophic hollows mosses were found to dominate in production, while the latter on the palsa sites was dominated by lichens, displaying great species diversity, significantly exceeding that of other plants. The other factors being equal, in hollow sites phytomass stocks and yearly production increased with increased nutrient availability, being decreased on palsa sites due to the permafrost layer. Analysis of phytomass production in northern taiga mires allows concluding that soil characteristics play important role in phytomass production, which was found to be rather low overall. Phytomass stock and production on palsa sites are limited by shallow thawing depths, which effect is exacerbated by drying and warming of the upper soil layer in summer, altogether resulting in unfavourble environment for root growth and development.