Experimental strategies to measure the microbial uptake and mineralization kinetics of dissolved organic carbon in soil

Abstract

Soil organic matter turnover rates are typically estimated from mass loss of the material over time or from on rates of carbon dioxide production. In the study, we investigated a new way to characterize the concentration-dependent kinetics of amino acids used by measuring microbial uptake and mineralization of ¹⁴C-alanine. We measured the depletion from soil solution after additions ¹⁴C-alanine. The microbial uptake of ¹⁴C-alanine from soil solution was concentration dependent and kinetic analysis indicated the operation of at least three distinct alanine transport systems of differing affinities. Most of the ¹⁴C-alanine depletion from the soil solution occurred rapidly within the first 10 – 30 min of the incubation after 10 μM to 1 mM substrate additions. At alanine concentrations less than 250 μM, the kinetic parameters for K_m and V_max of the higher-affinity transporter were 60.0 μM and 1.32 μmol g⁻¹ DW soil h⁻¹, respectively. The mineralization of alanine was determined and the half-time values for the rapid mineralization process were 45 min to 1.5 h after the addition at alanine concentrations below 1 mM. The time delay after its uptake into microbial biomass suggested that alanine uptake and subsequent respiration was uncoupled pattern. The microbial N uptake rate was calculated by microbial mineralization, and an estimated the K_m value of 1731.7±274.6 μM and V_max value of 486.0±38.5 μmol kg⁻¹ DW soil h⁻¹. This study provides an alternative approach for measuring the rate of turnover of compounds that turnover very rapidly in soil.

Keywords

¹⁴C tracer / Microbial uptake / Carbon mineralization / Turnover

References

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