ACCUMULATION OF ORGANIC-MATTER ALONG A POLLUTION GRADIENT - APPLICATION OF ODUMS THEORY OF ECOSYSTEM ENERGETICS

Forest soil biology in Scots pine forests of the Empetrum-Vaccinium ty pe was studied around the industrialized city of Oulu, northern Finlan d since 1987. The forest sites lie along a sulphur and nitrogen concen tration gradient in the mor humus ranging from 1.6 to 3.9 mg S g(-1) o rganic matter (OM) and from 14 to 23 mg N g(-1) OM. A number of biolog ical parameters have earlier been found to vary along this gradient, t hus indicating that the ecosystems are subjected to a pollution stress . Total microbial biomass and various activity parameters were studied in 1991. The different methods are discussed and the results interpre ted within the light of Odum's theory of the energetic stabilization o f ecosystems. Microbial biomass C determined by the fumigation-extract ion (FE) technique varied from 5 to 10 mg g(-1) OM, N from 0.5 to 1.0 mg g(-1) OM, and basal respiration rate from 0.040 to 0.097 mg CO2 h(- 1) g(-1) OM. All decreased along the pollution gradient. Substrate ind uced respiration values (SIR) varied from 0.025 to 0.085 mg CO2-C h(-1 ) g(-1) dw. SIR correlated well with the biomass values determined by the FE technique. The lag time of the microbial community after glucos e addition (varying from 13 to 22 h) was shortened and the specific re spiration increment of the microbial community in response to glucose addition increased along the gradient. The metabolic quotient (respira tion/biomass) of the microflora strongly depended on the technique and equation used in calculating the microbial biomass. The results show a reduced biomass, but a more intensive regeneration and intensified a ctivity per biomass unit of microorganisms in polluted forest soil. Th is in turn denotes an alteration in the microbial community in favor o f a higher proportion of r-strategists under the disturbed conditions. In contrast, K-strategists may be more dominant under less polluted c onditions. This interpretation is presented with some reservations con cerning methodology. There is a need for the calibration of each metho d for determining microbial biomass in different types of soil.