【收土地利用与土壤深度影响的可溶有机质生物降解】Ehsan R. Toosi Peter W. Clinton Michael H. Beare and David A. Norton. Biodegradation of Soluble Organic Matter as Affected by Land-Use and Soil Depth. SSSAJ Vol. 76 No. 5 p. 1667-1677

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.

【超声破坏土壤团聚体提高土壤有机质矿化和迁移】Carsten W. Mueller Svetlana Schlund Jörg Prietzel Ingrid Kögel-Knabner and Martin Gutsch. Soil Aggregate Destruction by Ultrasonication Increases Soil Organic Matter Mineralization and Mobility. SSSAJ Vol. 76 No. 5 p. 1634-1643

Abstract

Ultrasonication is widely used in soil organic matter (SOM) fractionation studies to break up soil aggregates to disperse the soil into its primary particles. An increasing number of studies also aim to incubate SOM fractions obtained by physical soil fractionation to study the bioavailability of different soil organic C (SOC) pools. To evaluate possible influences of ultrasonic soil disruption on short-term SOM bioavailability as well as the content and composition of water-extractable organic matter (WEOM) and salt-extractable (10 mM K₂SO₄) organic matter (SEOM) we conducted a laboratory incubation experiment with aggregated soil material from an Ap horizon of a cropland soil. Bulk soil and subsamples in which aggregates had been