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Biodegradation of Soluble Organic Matter as Affected by Land‐Use and Soil Depth
Author(s) -
Toosi Ehsan R.,
Clinton Peter W.,
Beare Michael H.,
Norton David A.
Publication year - 2012
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2011.0437
Subject(s) - biodegradation , subsoil , organic matter , chemistry , environmental chemistry , topsoil , biogeochemical cycle , incubation , soil organic matter , soil water , soil horizon , soil science , organic chemistry , environmental science , biochemistry
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 CaCl 2 ) and salt (0.5 mol L −1 K 2 SO 4 ) 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 δ 13 C (close to soil organic matter [SOM]), C/N ratio, and proportion of aromatic compounds (determined by specific ultraviolet absorbance at 254 nm [SUVA 254 ]) for SEOM. For both C and N, the turnover of the slowly biodegradable pool explained the lower biodegradability of SEOM. Depletion in 13 C along with an increase in SUVA 254 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.