Estimating the active and total soil microbial biomass by kinetic respiration analysis

A model describing the respiration curves of glucose-amended soils was appl ied to the characterization of microbial biomass. Both lag and exponential growth phases were simulated. Fitted parameters were used for the determina tion of the growing and sustaining fractions of the microbial biomass as we ll as its specific growth rate (mu (max)) These microbial biomass character istics were measured periodically in a loamy silt and a sandy loam soil inc ubated under laboratory conditions. Less than 1% of the biomass oxidizing g lucose was able to grow immediately due to the chronic starvation of the mi crobial populations in situ. Glucose applied at a rate of 0.5 mg C g(-1) in creased that portion to 4-10%. Both soils showed similar dynamics with a pe ak in the growing biomass at day 3 after initial glucose amendment, while t he total (sustaining plus growing) biomass was maximum at day 7. The microo rganisms in the loamy silt soil showed a larger growth potential, with the growing biomass increasing 16-fold after glucose application compared to a sevenfold increase in the sandy loam soil. The results gained by the applie d kinetic approach were compared to those obtained by the substrate-induced respiration (SIR) technique for soil microbial biomass estimation, and wit h results from a simple exponential model used to describe the growth respo nse. SIR proved to be only suitable for soils that contain a sustaining mic robial biomass and no growing microbial biomass. The exponential model was unsuitable for situations where a growing microbial biomass was associated with a sustaining biomass. The kinetic model tested in this study (Panikov and Sizova 1996) proved to describe all situations in a meaningful, quantit ative and statistically reliable way.