Earthworm Bioturbation Research Articles

Introducing an improved multi-proxy approach for paleoenvironmental reconstruction of loess–paleosol archives applied on the Late Pleistocene Nussloch sequence (SW Germany)

To study paleoenvironmental and paleoclimatic changes in loess–paleosol sequences (LPS), most proxies except for screening parameters have often been applied at low sampling density, typically 1–2 per stratigraphic unit. This might lead to results that overlook paleovegetation effects that were not only restricted to paleosols but also affected underlying loess material. Here, a new profile was investigated in the loess–paleosol sequence (LPS) at Nussloch, SW Germany using a high resolution multi-proxy approach to improve our understanding of the Late Pleistocene record which serves as a standard sequence in Central Europe. This approach included several geophysical and geochemical parameters, as well as frequencies of root-related features.Grain size distribution and OSL dating enabled correlation of the new section with the nearby standard profile P4, revealing considerable variations of the thickness of stratigraphic units due to local small-scale variations in depositional conditions and paleogeomorphology of longitudinal greda structures. Magnetic susceptibility revealed weathering of the entire LPS under more humid conditions than those described for SE European and Chinese LPS. It further enabled a rough differentiation between an interval that was influenced by pedogenic processes (Lower Pleniglacial to lower part of the Upper Pleniglacial), and loess that was not markedly affected by soil formation. Color measurements confirmed these results and enabled the identification of several paleosols in the Upper Pleniglacial. For the uppermost part of the LPS, low magnetic susceptibility and inorganic geochemical parameters such as low Fe/Ti ratios indicated only weak or no pedogenic influence. In contrast, considerable variations e.g. in carbonatic carbon contents and organic carbon/nitrogen (C/N) ratio might be related to the high frequency of calcified root remains (up to 200rhizolithsm−2 and up to 12,500microrhizolithsm−2) in certain depth intervals of the LPS, entailing incorporation and degradation of organic matter. Frequencies of biopores, which are suggested to derive largely from former root growth and, to a lesser extent, from insect and earthworm bioturbation, were related to paleosols, and thus confirmed the pedostratigraphy.An improved assessment of terrestrial sedimentary archives can be achieved by high-resolution multi-proxy analysis and three-dimensional investigation of terrestrial sediments that are prone to bioturbation.

Earthworm bioturbation influences the phytoavailability of metals released by particles in cultivated soils

The influence of earthworm activity on soil-to-plant metal transfer was studied by carrying out six weeks mesocosms experiments with or without lettuce and/or earthworms in soil with a gradient of metal concentrations due to particles fallouts. Soil characteristics, metal concentrations in lettuce and earthworms were measured and soil porosity in the mesocosms was determined. Earthworms increased the soil pH, macroporosity and soil organic matter content due to the burying of wheat straw provided as food. Earthworm activities increased the metals concentrations in lettuce leaves. Pb and Cd concentrations in lettuce leaves can increase up to 46% with earthworm activities … These results and the low correlation between estimated by CaCl2 and EDTA and measured pollutant phytoavailability suggest that earthworm bioturbation was the main cause of the increase. Bioturbation could affect the proximity of pollutants to the roots and soil organic matter.

Carbon and nitrogen pools and fluxes above and below ground in spruce, pine and birch stands in southern Sweden

We synthesised results on soil carbon (C) and nitrogen (N) fluxes and the accumulation of soil organic C and N under adjacent 50-year-old Norway spruce, Scots pine and silver birch stands growing on similar soils and evaluated the different processes involved. C and N budgets were calculated. Spruce stands had larger stocks of C and N in biomass and soil than birch stands, with pine intermediate. The differences in soil stocks were mainly found in the organic layer, whereas differences in the mineral soil were small. The study showed that there is no simple answer to what is causing the differences in soil C and N stocks, because several processes are interacting. Spruce and pine trees had higher biomass and litter production than birch trees, but total litter inputs showed no significant difference between stands, because the rich ground vegetation under pine and birch contributed with substantial litter inputs, in contrast to the poor ground vegetation under spruce. Decomposition rate (per g of C) was markedly higher under birch than under spruce and pine resulting in lower C and N stocks in the organic layer. This effect was amplified by higher abundance and biomass of earthworms, favoured by higher pH and palatable litter under birch. Earthworm bioturbation probably both increased decomposition rate and damaged the ectomycorrhizal network with negative consequences for the formation of mycorrhizal litter and C storage. In conclusion, the direct effects of spruce, pine and birch litter on C and N pools and fluxes were modified by indirect effects of understorey structure, pH and earthworm responses.

Assessing daily egestion rates in earthworms: using fungal spores as a natural soil marker to estimate gut transit time

Earthworms have an important role in ‘bioturbation’—the mixing of soil due to biological processes. Quantification of earthworm bioturbation relies on estimating earthworm egestion rates which in turn depend on two parameters: the gut content of the worms and the gut transit time (GTT). Gut content can be determined relatively easily, but determining GTT is problematic. The present study aimed at estimating daily soil egestion rates of Aporrectodea caliginosa and Lumbricus terrestris, refining the most common approach for estimating GTT by using fungal spores as natural markers in ingested soil. This approach avoids the use of artificial markers that may adversely affect the earthworms. Gut transit time was estimated by tracking the passage of marked soil through the gut by the appearance of the spores in the egested faeces. Gut transit time was estimated to be 9.6 ± 0.3 h for A. caliginosa and 11.6 ± 0.5 h for L. terrestris. Gut content averaged 465 ± 40(± standard error (SE)) mg dw g−1 dw worm for A. caliginosa and 265 ± 80 mg dw g−1 dw worm for L. terrestris. From these values, daily egestion rates of 1.16 and 0.66 g dw faeces g−1 dw worm d−1 were calculated for A. caliginosa and L. terrestris, respectively. Both values compare well to literature values for each species. The presented method for GTT estimation is inexpensive, rapid and easy to evaluate, with spores being a good alternative to existing markers.

Is the effect of trees on soil properties mediated by soil fauna? A case study from post-mining sites

The effects of tree species differing in foliage and litter chemistry on the chemical, micro-morphological, and biological properties of soil were studied on post-mining sites afforested with one of six tree species (spruce, pine, larch, oak, lime, and alder) and also on sites left to natural succession (dominated by willow). The sites were located on a large colliery spoil heap that had been produced by the mining of coal in alkaline tertiary clays near the city of Sokolov, Czech Republic. Because no topsoil had been applied to the sites, soil development resulted from in situ interactions among the deposited overburden (spoil), trees, and soil biota. Soil formation differed markedly among sites afforested with different tree species. On sites with trees producing litter with a low C/N ratio (the deciduous species), the organic Oe layer was narrow or absent and a thick organomineral A layer was evident. On sites with trees producing litter with a high C/N ratio (the evergreen species), in contrast, a thick Oe layer and a thin A layer were evident. Besides C/N ratio, earthworm abundance and earthworm bioturbation activity (measured as the amount of earthworm casts in the topsoil) were the strongest predictors of A layer thickness and C accumulation in the mineral topsoil. Sites with higher C accumulation in mineral soil had higher microbial biomass and lower microbial respiration, which may have contributed to the higher C storage. The gradient of bioturbation was correlated with changes in the composition of the bacterial community and other soil biota, but partial correlation showed that the effects of litter quality and bioturbation were largely independent. Overall, the results indicate that the effect of tree species on soil development is substantially mediated by soil fauna activity and especially by earthworm bioturbation.

Earthworms, litter and soil carbon in a northern hardwood forest

The important role of soil carbon (C) in the global C cycle has stimulated interest in better understanding the mechanisms regulating soil C storage and its stabilization. Exotic earthworm invasion of northern forest soils in North America can affect soil C pools, and we examined their effects on these mechanisms by adding 13C labeled leaf litter to adjacent northern hardwood forests with and without earthworms. Two types of labeled litter were produced, one with the 13C more concentrated in structural (S) components and the other in non-structural (NS) components, to evaluate the role of biochemical differences in soil C stabilization. Earthworm invasions have reduced soil C storage in the upper 20 cm of the soil profile by 37 %, mostly by eliminating surface organic horizons. Despite rapid mixing of litter into mineral soil and its incorporation into aggregates, mineral soil C has not increased in the presence of earthworms. Incorporation of litter C into soil and microbial biomass was not affected by biochemical differences between S versus NS labeled litter although NS litter C was assimilated more readily into earthworm biomass and S litter C into fungal hyphae. Apparently, the net effect of earthworm mixing of litter and forest floor C into mineral soil, plus stabilization of that C in aggregates, is counterbalanced by earthworm bioturbation and possible priming effects. Our results support recent arguments that biochemical recalcitrance is not a major contributor to the stabilization of soil C.

Morphological description of soil structure patterns produced by earthworm bioturbation at the profile scale

In cultivated soils, Soil structure mainly results from climatic, anthropogenic and biological processes. Nevertheless, few field methods evaluating the quality of soil structure consider the contribution of biological processes. In order to include earthworm biostructures in the field description of soil-structure, an original method is proposed in this paper. Soil profiles under different agricultural practices were examined to distinguish soil-structure patterns, notably those resulting from earthworm bioturbation. The relevance of naked eye observation was tested by a micromorphological approach, using image analysis on thin sections. Then, the application of this method was illustrated by mapping soil profiles.Our study led to the creation of a typology (i.e. classification system) of eleven soil-structure patterns, taking into account anthropogenic processes (e.g. compaction, soil tillage), root activity and earthworm activity. Seven patterns were attributed to earthworm activity in the form of burrows or casts. Three burrow features were distinguished, differentiating between filled burrows, or empty burrows with a brown cutan or without visible cutan. Four patterns of cast packing were distinguished, differentiating between cast aggregates that were fresh, welded, compacted, or combined with burrow features. This typology appears relevant for developing a field tool to describe and spatially quantify soil structure.

What are the limits of the drilosphere? An incubation experiment using Metaphire posthuma

Abstract The near infrared reflectance spectroscopy (NIRS) method was used in the present study to compare earthworm-made soil aggregates to aggregates found in the surrounding bulk soil. After initially assessing the daily cast production of Metaphire posthuma , boxes with soil incubated with M. posthuma and control soils were subjected to wetting in order to reorganize the soil structure. After two months of incubation, soil aggregates produced by earthworms (casts and burrows), soil aggregates that were appeared to be unaffected by earthworms (bulk soil without visible trace of earthworm bioturbation from the earthworm treatment) and soil aggregates that were entirely unaffected by earthworms (control – no earthworm – treatment) were sampled and their chemical signatures analyzed by NIRS. The production of below-ground and surface casts reached 14.9 g soil g worm −1 d −1 and 1.4 g soil g worm −1 d −1 , respectively. Soil aggregates from the control soils had a significantly different NIRS signature from those sampled from boxes with earthworms. However, within the earthworm incubation boxes the NIRS signature was similar between cast and burrow aggregates and soil aggregates from the surrounding bulk soil. We conclude that the high cast production by M. posthuma and the regular reorganization of the soil structure by water flow in and through the soil lead to a relatively homogenous soil structure. Given these results, we question the relevance of considering the bulk soil that has no visible activity of earthworm activity as a control to determine the effect of earthworms on soil functioning.

Using X-ray tomography to quantify earthworm bioturbation non-destructively in repacked soil cores

X-ray tomography is used increasingly to study the macroporosity resulting from earthworm activity. However, macropores are not the only features visible on the images; other zones resulting from bioturbation by earthworms can be detected due to differences in greylevels. Four different soil cores were incubated with two earthworm species at two different densities (4 or 8 adults of the endogeic species Allolobophora chlorotica or 2 or 4 adults of the anecic species Aporrectodea nocturna). A fifth core without earthworms was used as a control. After six weeks, the cores were analysed by X-ray tomography using a medical scanner. The 3D earthworm burrow systems were reconstructed and a new and specific algorithm was used to determine other bioturbated zones (BZ) that were physically influenced by the earthworms. Expected differences in the structure of the burrow systems between the endogeic and anecic species were observed: the A. chlorotica burrows were narrower and more numerous, more branched and less vertical. When the earthworm density doubled, the volume and length of the A. chlorotica burrow system increased whereas no increase was observed for A. nocturna. The BZ, which were located in the upper section of the cores, represented almost the same volume as the macropores. These zones tended to be located further from the burrows in the A. chlorotica cores: 50% of the voxels corresponding to BZ were at a distance greater than 4 and 5.5 mm from the closest macropore for A. nocturna and A. chlorotica, respectively. Three processes may have contributed to form these zones, which are characterised by increased soil density: (i) soil compaction around the burrows during burrow creation, (ii) cast deposition in the burrows (burrow backfilling) and (iii) crushing of casts on the burrow walls (so called cutanes). The longer distance between BZ and macropores in A. chlorotica cores suggests that the proportion of burrow backfilling is higher for the endogeic species compared to the anecic species. If we assume that BZ located further than 10 mm from any burrow are actually burrows backfilled with casts, the volume of burrow backfilled in our study ranged from 14 to 18% for A. chlorotica and from to 8 to 10% for A. nocturna.

Earthworms as agents for arsenic transport and transformation in roxarsone-impacted soil mesocosms: A µXANES and modeling study

Earthworms influence soil mixing during their feeding and burrowing activities by causing physical displacement and chemical transformations, potentially impacting the distribution and speciation of soil contaminants. This study investigates the effects of burrowing earthworms on arsenic speciation and mobility in soil mesocosms treated with roxarsone, an increasing anthropogenic source of arsenic used in the poultry industry as a feed supplement. Experiments were designed to test the hypothesis that earthworms and burrows provide means for biotransformation and redistribution of arsenic. Arsenic distribution was determined following earthworm bioturbation in artificial soil columns that were initially constructed with a contaminated layer of designated thickness and depth. The resulting depth profiles were used to indicate bioturbation rates by fitting them to a simple one-dimensional advection/diffusion model with a biodiffusivity that decreases with depth. Synchrotron X-ray methods reveal additional small-scale displacement of arsenic near the burrow and in the bulk soil. Microbeam X-ray Absorption Near Edge Structure spectra were collected to determine arsenic speciation. Arsenic initially introduced as roxarsone tended to be in a methylated form after 30 days. Within the earthworm tissue, arsenic–glutathione complexes were formed. Results are viewed in the context of poultry litter used as agricultural fertilizer. A decrease in tillage arising from soil conservation efforts allows earthworm populations to increase and burrows to become more permanent. This study suggests that (1) burrows serve as macropores allowing rapid transport of arsenic to greater depths during infiltration events; (2) bioturbation rates appear to be depth-dependent; and (3) earthworm soil mixing produces potentially mobile forms of arsenic that may become bioaccessible as arsenic is transported through the subsurface.

Soil development on the WWI battlefield of Verdun, France

Much research has been done on how the physical environment can influence the outcome of battle, but few have studied the inverse: the effects of warfare upon the environment. The goal of this research is to characterize and help understand soil development within areas disturbed by explosive munitions on the WWI battlefield of Verdun, France (1916). Encompassing an area of 29,000 km 2, the battlefield remains one of the most heavily shelled of all time. Twenty-seven pedons were sampled and described, at three sites on the battlefield; some pedons were within artillery craters while others were on adjacent “undisturbed” soils. Site selection reflected the diversity of bedrock and drainage characteristics across the study area. Soil development was characterized within the crater bottoms and sides. Many craters penetrated the shallow limestone bedrock, and blasted out fragments of limestone on nearby undisturbed pedons had already been incorporated into the profile. Despite the short period of time since the battle (88 years), measurable amounts of weathering and pedogenesis has occurred in the soils within the craters. A major pedogenic process operative here is the accumulation and decomposition of organic matter, which is intimately associated with (and aided by) earthworm bioturbation. Based on elemental analysis of the fine earth fraction, measurable amounts of leaching and weathering have occurred in the 88 years since the battle. This study provides insight into the ability of a landscape to recover following a catastrophic anthropogenic disturbance.

The effect of two endogeic earthworm species on zinc distribution and availability in artificial soil columns

The objective of this study was to determine the impact of earthworm bioturbation on the distribution and availability of zinc in the soil profile. Experiments were carried out with Allolobophora chlorotica and Aporrectodea caliginosa in 24 perspex columns (∅ 10 cm), filled with 20–23 cm non-polluted soil (OM 2%, clay 2.9%, pH 0.01 M CaCl 2 6.4), that was covered by a 3–5 cm layer of aged zinc spiked soil (500 mg Zn/kg dry soil) and another 2 cm non-polluted soil on top. After 80 and 175 days, columns were sacrificed and each cm from the top down to a depth of 15 cm was sampled. Earthworm casts, placed on top of the soil, were collected. Each sample was analyzed for total and CaCl 2-exchangeable zinc concentrations. Effects of earthworm bioturbation were most pronounced after 175 days. For A. chlorotica, total and CaCl 2-exchangeable zinc concentrations in the polluted layers were lower with than without earthworms. Total zinc concentrations in the non-polluted layers were higher in columns with earthworms. Casts of A. chlorotica collected on the soil surface showed slightly higher total zinc concentrations than non-polluted soil. Casts were found throughout the whole column. For A. caliginosa there were no differences in total zinc concentration between columns with and without earthworms. CaCl 2-exchangeable zinc concentrations in the polluted layers were lower for columns with earthworms. Casts were mainly placed on top of the soil and contained total zinc concentrations intermediate between those in non-polluted and polluted soil layers. This study shows that different endogeic earthworm species have different effects on zinc distribution and availability in soils. A. chlorotica transfers soil throughout the whole column, effectively mixing it, while A. caliginosa decreases metal availability and transfers polluted soil to the soil surface.