Abstract
In temperate ecosystems, earthworms and ants are the most important organisms for bioturbation. Little is known about how these groups contribute to bioturbation in different environments and to what extent overall bioturbation depends on their diversity. We developed a formula that allows quantification of annual earthworm bioturbation, thereby taking differences between earthworm ecotypes into account. With this formula, we calculated earthworm bioturbation at three sites, each with vegetation types typically found in Northern Europe. Earthworm bioturbation was low (1 Mg dry soil ha−1 y−1) in Scots pine and Norway spruce forests with acidic soil (pH 3.9–4.4) and high (between 15 and 34 Mg dry soil ha−1 y−1) in broadleaf forests, grasslands, alder carr and spruce forests on calcareous soil. Burrowing (endogeic and anecic) earthworms accounted for most of the earthworm bioturbation, and these worms had the highest population densities at moderate-to-high soil pH (pH 5–7.2). Estimates of ant bioturbation at the same sites were based on nest abundance, size and residence time. Mean ant bioturbation varied between 0.2 and 1 Mg dry soil ha−1 y−1, but individual plots had up to 2.4 Mg dry soil ha−1 y−1. In soils with pH higher than 5, the relative contribution of ants to total bioturbation was only 1–5%. Ant bioturbation was higher than earthworm bioturbation only in some forest soils with pH 3.9–4.4. Thus, earthworms appear to be the dominant cause of bioturbation in most types of terrestrial ecosystems in the cold-temperate areas of Europe and when information on local earthworm communities and monthly soil temperatures is available, bioturbation can be quantified using the presented ‘earthworm bioturbation formula’.
Highlights
In cold-temperate regions, earthworms and ants are the most important ‘ecosystem engineers’ (Lavelle and others 1997; Jones and Gutierrez 2007)982 A.R
We studied the growth rate of field-sampled A. caliginosa at different temperatures in the laboratory and used the temperature dependence obtained from this growth study as a proxy for the temperature dependence of earthworm egestion, being aware of the fact that some ingestion and egestion can occur without any increase in body weight
These results indicate that soil pH and texture can be of equal importance as vegetation type (Ando and others 2008) and litter quality (Marichal and others 2011; Rajapaksha and others 2013) in determining earthworm bioturbation, exerting an indirect effect on bioturbation via modulating species composition and abundance of earthworm community
Summary
In cold-temperate regions, earthworms and ants are the most important ‘ecosystem engineers’ (Lavelle and others 1997; Jones and Gutierrez 2007)982 A.R. Earthworm and ant bioturbation contributes to a range of ecosystem services, like decomposition, nutrient cycling, soil structuring/formation and the regulation of water and gas exchange (Lavelle and others 2006; Wall and others 2012). The impact of bioturbation on individual services and the temporal and spatial dynamics of their bioturbation activity differ significantly between both groups (Folgarait 1998; Wilkinson and others 2009; Blouin and others 2013; Turbeand others 2010). This is, on the one hand, due to earthworms and ants having different spatial aggregation patterns, dispersal distances and life spans. There are only few studies that directly link the functioning of biological soil components like that of soil ecosystem engineers to ecosystem services (Adhikari and Hartemink 2016) because it is inherently difficulty to measure their impact on a particular ecosystem service under field conditions (Barrios 2007)
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