Accumulation of organic matter along a pollution gradient: Application of odum's theory of ecosystem energetics

Abstract

Forest soil biology in Scots pine forests of the Empetrum-Vaccinium type was studied around the industrialized city of Oulu, northern Finland since 1987. The forest sites lie along a sulphur and nitrogen concentration gradient in the mor humus ranging from 1.6 to 3.9 mg S g(-1) organic matter (OM) and from 14 to 23 mg N g(-1) OM. A number of biological parameters have earlier been found to vary along this gradient, thus 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 interpreted within the light of Odum's theory of the energetic stabilization of ecosystems. Microbial biomass C determined by the fumigation-extraction (FE) technique varied from 5 to 10 mg g(-)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 induced 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 glucose addition (varying from 13 to 22 h) was shortened and the specific respiration increment of the microbial community in response to glucose addition increased along the gradient. The metabolic quotient (respiration/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 activity per biomass unit of microorganisms in polluted forest soil. This in turn denotes an alteration in the microbial community in favor of a higher proportion of r-strategists under the disturbed conditions. In contrast, K-strategists may be more dominant under less polluted conditions. This interpretation is presented with some reservations concerning methodology. There is a need for the calibration of each method for determining microbial biomass in different types of soil.