Analisis

Soil Biology & Biochemistry 42 (2010) 418e428

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Soil Biology & Biochemistry
journal homepage: www.elsevier.com/locate/soilbio

Microbial respiration activities related to sequentially separated, particulate and water-soluble organic matter fractions from arable and forest topsoils
M. Kaiser a, *,1, S. Wirth b, R.H. Ellerbrock a, M. Sommer a, c
aLeibniz-Centre for Agricultural Landscape Research (ZALF) e.V., Institute of Soil Landscape Research, Eberswalder Strasse 84, 15374 Müncheberg, Germany Leibniz-Centre for Agricultural Landscape Research (ZALF) e.V., Institute of Landscape Matter Dynamics, Eberswalder Strasse 84, 15374 Müncheberg, Germany c University of Potsdam, Institue of Geoecology, Karl-Liebknecht Str. 24-25, 14476 Potsdam,Germany
b

a r t i c l e i n f o
Article history: Received 22 June 2009 Received in revised form 2 November 2009 Accepted 16 November 2009 Available online 3 December 2009 Keywords: Sequential separation Physically uncomplexed Macro-aggregate occluded Micro-aggregate occluded Labile organic matter fractions Biodegradable Microbial activity Land use

a b s t r a c t
This study aimed toreveal differences in the relevance of particulate as well as water-soluble organic matter (OM) fractions from topsoils to the easily biodegradable soil organic matter (SOM). We selected eight paired sites with quite different soil types and soil properties. For each of these sites, we took samples from adjacent arable and forest topsoils. Physically uncomplexed, macro-, and micro-aggregate-occludedorganic particle, as well as water-soluble OM fractions were sequentially separated by a combination of electrostatic attraction, ultrasonic treatment, density separation, sieving, and water extraction. The easily biodegradable SOM of the topsoil samples was determined by measuring microbial respiration during a short-term incubation experiment (OCR). The organic carbon (OC) contents separated byi) the physically uncomplexed water-soluble OM, ii) the macro-, and iii) the micro-aggregate-occluded organic particle as well as water-soluble OM fractions were significantly correlated with OCR. The correlation coefficients vary between 0.54 and 0.65 suggesting differences in the relevance of these OM fractions to the easily biodegradable SOM. The strongest correlation to OCR was detected for theOC content separated by the physically uncomplexed water-soluble OM indicating the most distinct relation to the easily biodegradable SOM. This was found to be independent from land use or soil properties. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Microbial decomposition of soil organic matter (SOM) accounts for roughly half of CO2 evolution from vegetated soil surfaces (Wagaiand Sollins, 2002) and plays a crucial role in the ecosystem nutrient cycling, in the development of soil structure, i.e., aggregation, and for the potential of soils to contribute to the greenhouse effect, among others. Sequestration of organic carbon (OC) in soils will occur if the OC input is greater than the SOM loss caused by microbial decomposition. Carbon sequestration depends on factors suchas land use, pedogenetic properties, and management practices, as well as on soil moisture, temperature, and the depth of the topsoil that contains the bulk of SOM, plant roots, and microbial biomass. However, bulk SOM represents a heterogeneous mixture of operationally defined fractions that are characterised by differing compositions, microbial degradability and turnover time (von Lützow et al.,2006). The separation and identification of labile organic
* Corresponding author. Tel.: þ1 209 288 4170. E-mail address: mkaiser@ucmerced.edu (M. Kaiser). 1 Actual address: University of California Merced, School of Natural Science, 4225 N. Hospital Road, Atwater, CA 95301, USA. 0038-0717/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2009.11.018

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