Microbial uptake of low-molecular-weight organic substances out-competes sorption in soil
- Publication Type
- Journal contribution (peer reviewed)
- Authors
- Fischer H, Ingwersen J, Kuzyakov Y
- Year of publication
- 2010
- Published in
- European Journal of Soil Science
- Editor
- British Society of Soil Science
- Band/Volume
- 61/
- DOI
- 10.1111/j.1365-2389.2010.01244.x
- Page (from - to)
- 504-513
Low-molecular-weight organic substances (LMWOS) such as amino acids, sugars and carboxylates, are rapidly turned over in soil. Despite their importance, it remains unknown how the competition between microbial uptake and sorption to the soil matrix affects the LMWOS turnover in soil solution. This study describes the dynamics of LMWOS fluxes (10 μm) in various pools (dissolved, sorbed, decomposed to CO2 and incorporated into microbial biomass) and also assesses the LMWOS distribution in these pools over a very wide concentration range (0.01–1000 μm). Representatives of each LMWOS group (glucose for sugars, alanine for amino acids, acetate for carboxylates), uniformly 14C-labelled, were added to sterilized or nonsterilized soil and analysed in different pools between 1 minute and 5.6 hours after addition. LMWOS were almost completely taken up by microorganisms within the first 30 minutes. Surprisingly, microbial uptake was much faster than the physicochemical sorption (estimated in sterilized soil), which needed 60 minutes to reach quasi-equilibrium for alanine and about 400 minutes for glucose. Only acetate sorption was instantaneous.
At a concentration of 100 μm, microbial decomposition after 4.5 hours was greater for alanine (76.7 ± 1.1%) than for acetate (55.2 ± 0.9%) or glucose (28.5 ± 1.5%). In contrast, incorporation into microbial biomass was greater for glucose (59.8 ± 1.2%) than for acetate (23.4 ± 5.9%) or alanine (5.2 ± 2.8%). Between 10 and 500 μm, the pathways of the three LMWOS changed: at 500 μm, alanine and acetate were less mineralized and more was incorporated into microbial biomass than at 10 μm, while glucose incorporation decreased.
Despite the fact that the LMWOS concentrations in soil solution were important for competition between sorption and microbial uptake, their fate in soil is mainly determined by microbial uptake and further microbial transformations. For these substances, which represent the three main groups of LMWOS in soil, the microbial uptake out-competes sorption.