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DIVISION S-3—SOIL BIOLOGY & BIOCHEMISTRY

Preferential Accumulation of Microbial Carbon in Aggregate Structures of No-Tillage Soils

^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

^* Corresponding author (serita.frey{at}unh.edu).

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.

Abbreviations: BAS-C, bacterial-derived amino sugar carbon • CT, conventional tillage • FAS-C, fungal-derived amino sugar carbon • Gal, galactosamine • Glc, glucosamine • MurA, muramic acid • NT, no-tillage • POM, particulate organic matter • SOM, soil organic matter

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