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This article in SSSAJ

  1. Vol. 68 No. 4, p. 1249-1255
    Received: Sept 30, 2003

    * Corresponding author(s): serita.frey@unh.edu
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Preferential Accumulation of Microbial Carbon in Aggregate Structures of No-Tillage Soils

  1. Rodney T. Simpsona,
  2. Serita D. Frey *a,
  3. Johan Sixb and
  4. Rachel K. Thieta
  1. a Dep. of Natural Resources, Univ. of New Hampshire, Durham, NH 03824
    b Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616


We examined the effect of reduced tillage on the accumulation of fungal- versus bacterial-derived organic matter within the soil matrix by quantifying the amino sugars glucosamine (Glc), galactosamine (Gal), and muramic acid (MurA) in aggregate-size fractions isolated from no-tillage (NT) and conventional-tillage (CT) soil. Intact soil cores (0- to 5- and 5- to 20-cm depth) were collected from the long-term tillage experiment at Horseshoe Bend in Athens, GA. Four water-stable aggregate-size fractions were isolated: large macroaggregates (>2000 μm), small macroaggregates (250–2000 μm), microaggregates (53–250 μm), and the silt + clay fraction (<53 μm). Small macroaggregates were further separated into coarse particulate organic matter (POM) (>250 μm), microaggregates contained within macroaggregates, and the silt + clay fraction. Amino sugars were extracted from all fractions, purified, and analyzed by gas chromatography. Fungal-derived amino sugar C (FAS-C) comprised 63%, while bacterial-derived amino sugar C (BAS-C) accounted for 37% of the total amino sugar C pool under both tillage treatments. No-tillage soil contained 21% more amino sugar C than the CT soil across the entire plow layer. Both, the percentage of total organic C as FAS-C and BAS-C were significantly higher in the silt + clay fraction of NT versus CT soil. The percentage of total organic C as FAS-C was significantly higher in small macroaggregates of NT versus CT soil due to a preferential accumulation of FAS-C in the microaggregates contained within these macroaggregates. These results indicate that microbial-derived C is stabilized in NT soils, due primarily to a greater fungal-mediated improvement of soil structural stability and concurrent deposition of fungal-derived C in microaggregates contained within macroaggregates.

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