Comparison of microbial properties measured by O-2 consumption and microcalorimetry as bioindicators in forest soils

Microbial biomass C was determined in surface organic horizons and in the t op 15 cm of the mineral soil of five European coniferous forests. Both oxyg en-consumption and heat production following glucose addition were used to measure microbial biomass C. The undisturbed soils showed a marked gradient down the profile with regard to organic C and total N content and microbia l biomass. Average values of microbial biomass decreased from the fresh fal len litter in the L horizon (range in five soils) to the B horizon in all f ive mineral soils from 6667 to 227 mu g g(-1) DW (O-2-consumption) and from 7555 to 206 mu g g(-1) DW (heat production), respectively. Correlation ana lysis between results of O-2-consumption and heat production was carried ou t using the data from the analysis of complete soil profiles with that from single horizons. The results of both methods for measuring microbial bioma ss C were, in general, highly correlated (P < 0.01). Significant correlatio ns were also found between the results of both methods for measuring microb ial activity. The correlations between soil chemical properties (pH(CaCl2), organic C, total N and C-to-N ratio) and microbial biomass C indicated ver y similar relationships for both methods. There were significant relationsh ips (P < 0.05) of microbial biomass C to Ph in F- and H-layers, and in the mineral horizons of microbial biomass to pH, soil organic C and total N. Th e specific activity of microbial biomass was calculated as the metabolic qu otient (mu g O-2 mg(-1) C-mic h(-1) [C-mic detected by O-2-consumption]) an d the caloric quotient (mu W mg(-1) C-mic [C-mic detected by heat productio n]). Specific activity showed different patterns with depth and between soi ls. Metabolic quotient and caloric quotient were poorly correlated and indi cate the limitations of specific activity as a bioindicator in forest soils . (C) 1999 Elsevier Science Ltd. All rights reserved.