The role of microarthropods in terrestrial decomposition: a meta‐analysis of 40 years of litterbag studies

Abstract

Litterbags have been utilized in soil ecology for about 50 years. They are useful because they confine organic material and thus enable the study of decomposition dynamics (mass loss and/or nutrient loss through time, colonization by soil biota) in situ, i.e. under field conditions. Researchers can easily restrict or permit access to certain size classes of soil fauna to determine their contribution to litter mass loss by choosing adequate mesh size or applying specific biocides. In particular, the mesofauna has received much attention since it comprises two very abundant and diverse microarthropod groups, the Collembola (springtails) and Acari (mites). We comprehensively searched the literature from the mid-1960s to the end of 2005 for reports on litterbag experiments investigating the role of microarthropods in terrestrial decomposition. Thirty papers reporting 101 experiments satisfied our selection criteria and were included in the database. Our meta-analysis revealed that microarthropods have a moderate but significant effect on mass loss. We discuss in detail the interactions of the microarthropod effect with study characteristics such as experimental design (e.g. number of bags, duration of experiment), type of exposed organic matter, climatic zone and land use of the study site. No publication bias was detected; however, we noticed a significant decrease in the microarthropod effect with publication year, indicating that, in the first decades of litterbag use, soil zoologists may have studied "promising" sites with a higher a priori probability of positive microarthropod effects on litter mass loss. A general weakness is that the treatments differ not only with respect to the presence or absence of microarthropods, but also with regard to mesh size (small to exclude microarthropods, wide to permit their access) or presence (to exclude microarthropods) and absence (to permit their access) of an insecticide. Consequently, the difference between the decomposition rates in the treatments is not a pure microarthropod effect but will be influenced by the additive effects of mesh size and insecticide. The relative contribution of the "true" microarthropod effect remains unknown without additional treatments controlling for the differential mesh size/insecticide effect. A meta-analysis including only those studies using different mesh size and for which the data were corrected by subtracting an estimated mesh size effect based on data from the literature yielded a significantly negative microarthropod effect on litter decomposition. These results cast doubt on the widely accepted hypothesis that microarthropods generally exert a positive effect on litter mass loss. We conclude that after 40 years of litterbag studies our knowledge on the role of microarthropods in litter mass loss remains limited and that the inclusion of a third treatment in future studies is a promising way to retain litterbags as a meaningful tool of soil biological studies.

Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils?

“…Incorporating the biological activities of soil fauna and their effects on litter decomposition processes and pathways is perhaps the greatest remaining challenge. The recent meta-analysis of the effects of microarthropods on litter decomposition rates (Kampichler and Bruckner 2009) makes clear how poorly we understand this important effect: a slightly positive overall effect on decomposition was reversed when the authors incorporated the estimated side-effects of the unsatisfactory methodological approach of comparing mass loss in fine and coarse-mesh bags as an estimate of faunal influence. The authors also present some interesting evidence for an early publication or submission bias towards publication of data which supported the assumed stimulation of decomposition by soil fauna; more recent studies tend to show negative or neutral effects of fauna (to the extent to which either the coarse-mesh-bag or the naphthalene approach truly reflects faunal influence).…”

Landscape-Scale Implications of the Edge Effect on Soil Fauna Activity in a Temperate Forest

“…Soil fauna are key contributors to soil and litter respiration, they breakdown and recycle organic material, affect microbial activity, and are important ecosystem engineers (Seastedt 1984;Hassall and others 2006;Lavelle and others 2006;Osler and Sommerkorn 2007;Kampichler and Bruckner 2009). Temperature and moisture are the main drivers determining the activity and density of the soil fauna (Liiri and others 2002;Gongalsky and others 2008;Makkonen and others 2011), with reduced abundance and activity being found at the forest edges compared with the forest core (Haskell 2000;Simpson and others 2012).…”

Differential contribution of soil biota groups to plant litter decomposition as mediated by soil use

“…Indeed, results from previous authors (Brussaard et al, 2007;Kampichler and Bruckner, 2009) The results from the most disturbed system, the Intensive Agriculture, show the Mesofauna as the relevant group, for the only significant decrease in decomposition rate takes place when this group is excluded. These results are thoroughly consistent with the hierarchical model proposed by Lavelle et al (1993).…”

“…Despite their recognized importance, the interactions between the different groups of the soil biota are still largely unknown and one of the most studied topics in soil ecology (Hättenschwiler et al, 2005;Fitter et al, 2005;Kampichler and Bruckner, 2009;Culliney, 2013). Coûteaux et al (1991) and Bradford et al (2002) found a significant increase in the decomposition rates when these three groups (micro, meso and macrofauna) were found acting together, when compared to less complex soil fauna groups.…”