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Appl. Environ. Microbiol., Oct 1995, 3667-3675, Vol 61, No. 10
K Kusel and HL Drake
The capacity to form acetate from endogenous matter was a common property
of diverse forest soils when incubated under anaerobic conditions. At 15 to
20(deg)C, acetate synthesis occurred without appreciable delay when forest
soils were incubated as buffered suspensions or in microcosms at various
percentages of their maximum water holding capacity. Rates for acetate
formation with soil suspensions ranged from 35 to 220 (mu)g of acetate per
g (dry weight) of soil per 24 h, and maximal acetate concentrations
obtained in soil suspensions were two- to threefold greater than those
obtained with soil microcosms at the average water holding capacity of the
soil. Cellobiose degradation in soil suspensions yielded H(inf2) as a
transient product. Under anaerobic conditions, supplemental H(inf2) and
CO(inf2) were directed towards the acetogenic synthesis of acetate, and
enrichments yielded a syringate-H(inf2)-consuming acetogenic consortium. At
in situ temperatures, acetate was a relatively stable anaerobic end
product; however, extended incubation periods induced acetoclastic
methanogenesis and sulfate reduction. Higher mesophilic and thermophilic
temperatures greatly enhanced the capacity of soils to form methane.
Although methanogenic and sulfate-reducing activities under in
situ-relevant conditions were negligible, these findings nonetheless
demonstrated the occurrence of methanogens and sulfate-reducing bacteria in
these aerated terrestrial soils. In contrast to the protracted stability of
acetate under anaerobic conditions at 15 to 20(deg)C with unsupplemented
soils, acetate formed by forest soils was rapidly consumed in the presence
of oxygen and nitrate, and substrate-product stoichiometries indicated that
acetate turnover was coupled to oxygen-dependent respiration and
denitrification. The collective results suggest that acetate formed under
anaerobic conditions might constitute a trophic link between anaerobic and
aerobic processes in forest soils.
Copyright © 1995, American Society for Microbiology
Effects of Environmental Parameters on the Formation and Turnover of Acetate by Forest Soils
Lehrstuhl fur Okologische Mikrobiologie, BITOK, Universitat Bayreuth, 95440 Bayreuth, Germany
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