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Reversible transition between active and dormant microbial states in soil.
J Stenström1, K Svensson, M Johansson
1Department of Microbiology, Swedish University of Agricultural Sciences, P.O. Box 7025, SE-750 07, Uppsala, Sweden
FEMS Microbiology Ecology
|July 14, 2001
Summary
Soil microbial respiration involves growing (r) and non-growing (K) states, with substrate availability dictating their proportions. Glucose addition rapidly shifts microbes to the active (r) state, which then slowly reverts to the dormant (K) state over weeks.
Area of Science:
- Soil Microbiology
- Biogeochemical Cycles
- Microbial Ecology
Background:
- Substrate-induced respiration (SIR) quantifies microbial activity, differentiating between growing (r) and non-growing (K) biomass fractions.
- The proportion of r and K microorganisms in soil is influenced by substrate availability, suggesting dynamic transitions.
- Understanding these transitions is crucial for soil carbon cycling and nutrient dynamics.
Purpose of the Study:
- To investigate the reversibility and dynamics of transitions between growing (r) and non-growing (K) microbial states in soil.
- To determine the influence of substrate availability (glucose) and pre-incubation time on these microbial state shifts.
- To test hypotheses regarding substrate-driven reversible transitions and community-level controls on microbial growth.
Main Methods:
- Addition of varying glucose concentrations to three different soils with four pre-incubation times (4-46 days).
- Measurement of respiration rates using the substrate-induced respiration (SIR) method.
- Correction for abiotic CO(2) flush and analysis of CO(2)-C mineralization kinetics.
Main Results:
- Glucose addition rapidly increased respiration (SIR), indicating a shift from non-growing (K) to growing (r) states.
- This elevated respiration reverted to baseline levels within 27-46 days, demonstrating a slow back-transition from r to K.
- The rate of K to r transition correlated with initial glucose concentration, while the back-transition half-lives varied among soils (12-70 days).
Conclusions:
- Soil microbial biomass dynamics involve reversible oscillations between active (r) and dormant (K) physiological states.
- Microbial specific activity responds sharply to substrate availability, transitioning between dormant and fully active states rather than continuously.
- Community-level controls appear to regulate growth, potentially inhibiting it until the biomass is fully in the active (r) state.