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This article in SSSAJ

  1. Vol. 76 No. 5, p. 1667-1677
     
    Received: Nov 15, 2011
    Published: September 12, 2012


    * Corresponding author(s): etoosi@msu.edu
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doi:10.2136/sssaj2011.0437

Biodegradation of Soluble Organic Matter as Affected by Land-Use and Soil Depth

  1. Ehsan R. Toosi *a,
  2. Peter W. Clintonb,
  3. Michael H. Bearec and
  4. David A. Nortond
  1. a School of Froestry, Univ. of Canterbury, Christchurch, New Zealand, Currently at:Natural Resources Building, 480 Wilson Road, Michigan State University, East Lansing, MI 48824-1222
    b SCION, P.O. BOX 29237, Christchurch, New Zealand
    c New Zealand Institute for Plant and Food Research, Canterbury Agriculture and Science Centre, Private Bag 4704, Christchurch, New Zealand
    d School of Forestry, Univ. of Canterbury, Private Bag 4800, Christchurch, New Zealand

Abstract

Determining the biodegradability of soluble organic matter (OM) is important in understanding its role in biogeochemical cycles. We evaluated C and N biodegradation for two frequently studied fractions of soluble OM, water (0.01 mol L−1 CaCl2) and salt (0.5 mol L−1 K2SO4) extractable organic matter (WEOM and SEOM, respectively). Soil samples were collected from topsoil (0–20 cm) and subsoil (60–80 cm) at four sites across a long-term established land-use sequence. The biodegradation dynamics of WEOM and SEOM were determined during a 90-d laboratory incubation using a two-pool model. Compared with SEOM, the amount of C and N of WEOM further varied with land-use and soil depth. The proportion of biodegradable C and N was considerably larger for WEOM than SEOM, consistent with greater δ13C (close to soil organic matter [SOM]), C/N ratio, and proportion of aromatic compounds (determined by specific ultraviolet absorbance at 254 nm [SUVA254]) for SEOM. For both C and N, the turnover of the slowly biodegradable pool explained the lower biodegradability of SEOM. Depletion in 13C along with an increase in SUVA254 demonstrated a preferential consumption of labile compounds that were mainly mineralized during the initial 16 d of the incubation. The proportionally lower biodegraded C than N for both fractions was due to the longer half-life of the slowly biodegradable C. Both soil depth (only for WEOM) and land-use affected the proportion of the biodegradable pools (fast vs. slow) of C and N. In addition, land-use strongly influenced the turnover rate of the fast biodegradable pool. There was no evidence that soluble organic C and N from subsoil are less biodegradable than those of topsoil.

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Copyright © 2012. Copyright © by the Soil Science Society of America, Inc.