Carbon Concentrations and Caloric Value of Organic Matter in Northern Forest Ecosystems

Key words: north, taiga, forest ecosystems, carbon, caloric value.

The data on the carbon content in different plant organs and their caloric value are necessary for evaluat-ing the bioproduction process in phytocenoses and for studying the carbon cycle and energy and mass exchange in forest biogeocenoses. According to published data, the carbon content in individual biomass fractions amounts to 50–57% of their dry weight in conifers and to 42–48% in deciduous woody plants (Risser, 1985; Kobak, 1988; Vogt, 1991). Most of researchers estimating carbon stock in forest communities assume that it accounts for 50% of the absolutely dry weight of trunk, roots, and branches and for 45–50% of the weight of green plant parts (Makarevskii, 1991; Bidsey, 1990; Uglerod v ekosiste-makh…, 1994; Tsel’niker and Malkina, 1994; Kobak, 1989; Isaev et al., 1993, 1996). The caloric value of plant components in the ecosystems of forest zone is better studied (Ovington, 1961; Golley, 1961; Kur-batskii, 1962; Molchanov, 1971; Kononenko, 1975; Dadykin and Kononenko, 1975; Dem’yanov, 1974, 1981; Ivask, 1983, 1985; Vookova, 1985).

Utkin (1986) thoroughly analyzed the available data on the caloric values of plants and animals. He found that the heat of plant combustion as a physical parame-ter is characterized by a relatively high variability, being dependent on plant species, growing conditions, morphological structure, age, period of sampling, and other factors. However, many aspects of plant differen-tiation with respect to their caloric value remain unclear. Special studies are necessary for elucidating the relationships between the heat of plant combustion and multiple environmental factors, the intensity of physiological processes, and the biochemical composi-tion of organic matter synthesized and accumulated by plants. Moreover, publications provide virtually no data on the carbon content and caloric value of organic mat-ter in forest ecosystems of the European Northeast. The purpose of this work was to determine the car-bon content and caloric value of different phytomass fractions. The following plants were studied: trees Pinus sylvestrisL., Picea obovataLedeb., Betula pen-dulaRoth., Populus tremulaL., and Larix sibirica Ledeb., Fl. Alt.; dwarf shrubs Vaccinium vitis-idaeaL., V. myrtillusL., and V. uliginosumL.; mosses Pleuro-zium schreberi, Hylocomium splendens, Polytrichum commune, and Sphagnumsp.; mixed herbaceous sam-ples including Trientalis europeaL., Maianthemum bifoliumL., Equisetum silvaticumL., and Agrostis tenuisSibth.; and lichens Cladinasp. The main compo-nents of plant fall and litter were also analyzed. The study was carried out in pine and spruce phyto-cenoses of the middle taiga subzone in the Komi Republic (62¡N, 50¡20′E). Plant samples for analysis were collected in the end of the growing period (August to September) simultaneously with estimating the phy-tomass of the plant communities. The carbon concen-trations in phytomass fractions were determined in an ANA-1500 automatic nitrogen and carbon analyzer (Carboro Erba, Italy); the caloric value, by the combus-tion method according to Kochan (1982). Measure-ments were made in ten biological and three to eight analytical replications. The experimental data were processed statistically by conventional methods. As follows from Tables 1 and 2, the range of carbon concentrations in different phytomass fractions of trees was 44.6–50.3% dry weight; in plants of the herb– dwarf shrub layer, 41.9–53.4%; in mosses and lichens, 42.3–45.4%; in forest litter, 45.8–48.2%; and in the components of plant fall, 44.6–53.1%. The carbon con-centrations in trees varied insignificantly: the coeffi-cient of variation (CV) was 2.4% for individual species and 1.5–4.3% for phytomass components within a spe-cies. The range of carbon concentrations in plants of ground vegetation was slightly higher, but the variation of this parameter by species did not exceed 10% in these plants and 2.8% in mosses and lichens. The car-bon concentrations in individual fractions of plant fall and different types of litter differed by 5 and 8.6%, respectively.

The analysis of data on the caloric value of tree plants shows that this parameter of individual phyto-mass fractions varied from 16.81 to 21.77 kJ/g in spruce, from 16.40 to 22.91 kJ/g in pine, from 17.91 to 21.56 kJ/g in larch, and from 16.66 to 20.95 kJ/g in birch (Table 3). The coefficients of variation were 10.3, 8.8, 7.0, and 5.2%, respectively. Higher energy values were typical of trunk wood and large roots. The caloric value of plants in the lower layers of coniferous communities varied from 17.44 to 19.76 kJ/g; of forest litter, from 17.37 to 18.46 kJ/g; and of plant fall, from 16.58 to 19.89 kJ/g. The variation in this parameter both in plants of ground vegetation and in the litter was insignificant: the coefficients of variation were 3.0 and 2.4%, respectively These data can be used for making up the energy and carbon balance and for studying energy flows in forest ecosystems of the taiga zone..