Decomposition of Quercus petraea litter: in¯uence of burial, comminution and earthworms M. McInerney * , T. Bolger Department of Zoology, University College Dublin, Bel®eld, Dublin 4, Ireland Accepted 21 April 2000 Abstract Litter bags containing one of the following: earthworm cast, intact oak litter (Quercus petraea Matt., Liebl.) plus soil and shredded oak litter (,2 mm) plus soil, were placed on the surface or buried at 7 cm in a forest soil. Over a 2-year period the six treatments were sampled on nine dates and analysed for mass loss, moisture content, C, N, bacterial numbers, fungal hyphal lengths, FDA and mineralization rates (evolution of CO 2 ). Earthworm casts (surface and buried) had reduced moisture ¯uctuations relative to non-cast (intact or shredded) treatments. Casts maintained higher levels of organic matter and carbon than non-cast treatments (surface or buried) after 2 years of decomposition. However, while both surface and buried casts maintained higher levels of organic matter, bacterial counts in buried cast remained higher than all other treatments (including surface cast) on ®ve of the seven ®nal sampling dates. Shredding and burial of organic matter did not affect total, cumulative loss of organic matter/carbon from the non-cast treatments. Potential mineralization rates (loss of CO 2 at 208C) from non-cast treatments was in¯uenced by their placement. When temperature and/or moisture became limiting surface non-cast treatments showed reduced losses of CO 2 by comparison with buried non-cast treatments. The reverse occurs when the moisture and temperature are not limiting, i.e. surface treatments have greater losses of CO 2 than the buried treatments. Thus, both the micro-climatic and soil aggregate effects (and their interactions) were observed to in¯uence the decay dynamics and are discussed in relation to nutrient stabilization/mobilization and microbial populations. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Earthworm casts; Organic matter stabilization; Seasonal factors; Moisture content; Carbon; Nitrogen; Fungi; Bacterial plate counts; Respiration 1. Introduction Most detritus, whether from litterfall or root turnover, is subject to decomposition by a vast array of primary decom- posers (including bacteria, fungi and fauna), whose popula- tions and rates of activity are determined by physical (primarily temperature and moisture) and chemical (resource quality) factors (Swift et al., 1979). Hence, litter breakdown rates are determined by a range of factors which operate at vastly different spatial and temporal scales (Wardle and Lavelle, 1997). Indeed, microclimate and not the general climate per se, may be the most important single factor (Stevenson, 1986). In addition, soil texture, micro- structure and the formation of organic±inorganic complexes play important roles in soil stabilization (Jenkinson, 1971; Sorensen, 1972; Ladd et al., 1975). In fact, increasing silt content increases water holding capacity, so that soil texture interacts with micro-climate in controlling these important ecosystem processes (Burke et al., 1989). Knowledge of the mechanisms involved in this stabilization (and changes in turnover rates) is a prerequisite for a better understanding of the fate of organic materials incorporated into soils (Chris- tensen, 1987). Animals such as earthworms play a major role in the structural development of soils (particularly loams), because they in¯uence the rate and extent of drying in soil (Oades, 1993). Further, earthworm casts contribute immen- sely to the chemical (Satchell, 1983) and microbial (Shaw and Pawluk, 1986; Tiwari and Mishra, 1993; Parle, 1963; Wolters and Joergensen, 1992) heterogeneity of soils (Shipitalo and Protz, 1988; Marinissen and Dexter, 1990). Physical heterogeneity is also increased since casting activ- ity has been shown to enhance aggregation (Blanchart et al., 1990), structural stability (De Vleeschauwer and Lal, 1981) and tensile strength (McKenzie and Dexter, 1987; Zhang and Schrader, 1993) of soils, but this stability appears to be greatly in¯uenced by water content and age. Thus, the compact structure of casts may result in tempor- ary immobilization, but also under certain moisture/ Soil Biology & Biochemistry 32 (2000) 1989±2000 0038-0717/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0038-0717(00)00097-3 www.elsevier.com/locate/soilbio * Corresponding author. Tel.: 1353-1-706-2265; fax: 1353-1-706-1152. E-mail address: michael.mcinerney@ucd.id (M. McInerney).