Summary
Biodiversity is responsible for the provision of many ecosystem services; human well‐being is based on these services, and consequently on biodiversity. In soil, earthworms represent the ...largest component of the animal biomass and are commonly termed ‘ecosystem engineers’. This review considers the contribution of earthworms to ecosystem services through pedogenesis, development of soil structure, water regulation, nutrient cycling, primary production, climate regulation, pollution remediation and cultural services. Although there has been much research into the role of earthworms in soil ecology, this review demonstrates substantial gaps in our knowledge related in particular to difficulties in identifying the effects of species, land use and climate. The review aims to assist people involved in all aspects of land management, including conservation, agriculture, mining or other industries, to obtain a broad knowledge of earthworms and ecosystem services.
BACKGROUND AND AIMS: Soil aggregate stability depends on plant community properties, such as functional group composition, diversity and biomass production. However, little is known about the ...relative importance of these drivers and the role of soil organisms in mediating plant community effects. METHODS: We studied soil aggregate stability in an experimental grassland plant diversity gradient and considered several explanatory variables to mechanistically explain effects of plant diversity and plant functional group composition. Three soil aggregate stability measures (slaking, mechanical breakdown and microcracking) were considered in path analyses. RESULTS: Soil aggregate stability increased significantly from monocultures to plant species mixtures and in the presence of grasses, while it decreased in the presence of legumes, though effects differed somewhat between soil aggregate stability measures. Using path analysis plant community effects could be explained by variations in root biomass, soil microbial biomass, soil organic carbon concentrations (all positive relationships), and earthworm biomass (negative relationship with mechanical breakdown). CONCLUSIONS: The present study identified important drivers of plant community effects on soil aggregate stability. The effects of root biomass, soil microbial biomass, and soil organic carbon concentrations were largely consistent across plant diversity levels suggesting that the mechanisms identified are of general relevance.
Phylogenetically closely related plant species often share similar trait states (phylogenetic signal), but local assembly may favor dissimilar relatives and thereby decouple the diversity of a trait ...from the diversity of phylogenetic lineages. Associated fauna might either benefit from plant trait diversity, because it provides them complementary resources, or suffer from it due to dilution of preferred resources. We hence hypothesize that decoupling of trait and phylogenetic diversity weakens the relationship between the plant-trait diversity and the abundance and diversity of associated fauna. Studying permanent meadows, we tested for combined effects of plant phylogenetic diversity and diversity of two functional traits (specific leaf area, leaf dry matter content) on major groups of soil fauna (earthworms, mites, springtails, nematodes). We found that only in phylogenetically uniform plant communities, was uniformity in the functional traits associated with (i) high abundance in springtails, and (ii) high abundance of the sub-group that feeds more directly on plant material (in springtails and mites) or those that are more prone to disturbance (in nematodes), and (iii) high diversity in all three groups tested (springtails, earthworms, nematodes). Our results suggest that soil fauna profits from the resource concentration in local plant communities that are uniform in both functional traits and phylogenetic lineages. Soil fauna would hence benefit from co-occurrence of closely related plants that have conserved the same trait values, rather than of distantly related plants that have converged in traits. This might result in faster decomposition and a positive feedback between trait conservatism and ecosystem functioning.
•The effect of reducing tillage on earthworms was assessed by a trait-based approach.•Three tillage types from four different sites were compared.•High soil tillage intensity reduces earthworm ...functional diversity.•4 out of 7 investigated traits were significantly affected by tillage intensity.
Alternative cropping systems such as conservation agriculture have been implemented to limit the harmful effects of intensive conventional cropping systems. Conservation agriculture is known to modify the structural diversity of earthworm communities, but no data have been reported so far on their functional diversity. Structural and functional indices of community were used to study the effects of different soil tillage intensity on earthworm diversity in arable soils.
Field data were collected in four agricultural trials across France representing different soiland climatic conditions. Three types of soil tillage were assessed: plowing, superficial tillage and direct seeding. Earthworm abundance, species richness and ecomorphological group abundance were investigated. Seven functional traits, i.e. body length, body mass/length ratio, epithelium type, cocoon diameter, typhlosolis type, carbon preferences and vertical distribution, were selected according to their hypothesized link with mechanisms of tillage impact. Functional diversity indices were then computed. Soil tillage intensity decreased functional diversity and modified the functional trait profile within the earthworm community whereas neither structural diversity (species number) nor abundance changed with tillage intensity. Differences between plowing and direct seeding were significant in each trial, and superficial tillage often showed intermediate trait values. Regarding ecomorphological groups, anecic abundance was positively influenced by a decrease in soil tillage, contrary to epigeic and endogeic earthworms that showed no response. Tillage acts as an environmental filter, and decreasing its intensity caused a lesser convergence of traits and thus higher functional trait diversity. We demonstrated that a trait-based approach better permitted comparisons of community responses across sites than species number or abundance.
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•Eighteen potential indicators selected using a logical sieve.•Indicators tested at six European sites across climatic zones.•No single indicator sensitive to all differences in land ...use intensity.•Recommended indicators for function are: earthworms; functional genes; and bait lamina.•For monitoring of biodiversity all taxonomic groups need to be addressed.
Soils provide many ecosystem services that are ultimately dependent on the local diversity and belowground abundance of organisms. Soil biodiversity is affected negatively by many threats and there is a perceived policy requirement for the effective biological monitoring of soils at the European level. The aim of this study was to evaluate and recommend policy relevant, cost-effective soil biological indicators for biodiversity and ecosystem function across Europe. A total of 18 potential indicators were selected using a logical-sieve based approach. This paper considers the use of indicators from the ‘top down’ (i.e. concerned with the process of indicator selection), rather than from the ‘bottom up’ detail of how individual indicators perform at specific sites and with specific treatments. The indicators assessed a range of microbial, faunal and functional attributes, newer nucleic acids based techniques, morphological approaches and process based measurements. They were tested at 6 European experimental sites already in operation and chosen according to land-use, climatic zone and differences in land management intensity. These were 4 arable sites, one each in Atlantic, Continental, Mediterranean and Pannonian climate zones, and 2 grassland sites, one each in Atlantic and Continental zones. At each site we sampled three replicated plots of contrasting management intensity and, while the treatments varied from site to site, their disturbance effects were quantified in terms of land use intensity. The field sampling and laboratory analysis were standardised through a combination of ISO protocols, or standard operating procedures if the former were not available. Sites were sampled twice, in autumn 2012 and spring or autumn 2013, with relative costs of the different indicators being determined each time. A breakdown of the cost effectiveness of the indicators showed the expected trade-off between effort required in the field and effort required in the laboratory. All the indicators were able to differentiate between the sites but, as no single indicator was sensitive to all the differences in land use intensity, we suggest that an indicator programme should be based upon a suite of different indicators. For monitoring under the European climatic zones and land uses of this study, indicators for ecosystem functions related to the services of water regulation, C-sequestration and nutrient provision would include a minimum suite of: earthworms; functional genes; and bait lamina. For effective monitoring of biodiversity all taxonomic groups would need to be addressed.
Vineyards show some of the largest erosion rates reported in agricultural areas in Europe. Reported rates vary considerably under the same land use, since erosion processes are highly affected by ...climate, soil, topography and by the adopted soil management practices. Literature also shows differences in the effect of same conservation practices on reducing soil erosion from conventional, bare soil based, management. The Revised Universal Soil Loss Equation (RUSLE) is commonly adopted to estimate rates of water erosion on cropland under different forms of land use and management, but it requires proper value of soil cover and management (C) factors in order to obtain a reliable evaluation of local soil erosion rates. In this study the ORUSCAL (Orchard RUSle CALibration) is used to identify the best calibration strategy against long-term experimental data. Afterwards, ORUSCAL is used in order to apply the RUSLE technology from farm based information across different European wine-growing regions. The results suggest that the best strategy for calibration should incorporate the soil moisture sub-factor (Sm) to provide better soil loss predictions. The C factor, whose average values ranged from 0.012 to 0.597, presented a large spatial variability due to coupling with local climate and specific local management. The comparison across the five wine-growing regions indicates that for the soil protection management, permanent cover crop is the best measure for accomplishing sustainable erosion rates across the studied areas. Alternate and temporary cover crops, that are used in areas of limited water resources to prevent competition with vines, failed to achieve sustainable erosion rates, that still need to be addressed. This raises the need for a careful use of C values developed under different environmental conditions.
Litter decomposition is central to ecosystem functioning and depends, under constant abiotic conditions, on litter quality and decomposer activity. During the assembly of a plant community following ...disturbance, litter quality is expected to decrease, due to an increasing proportion of resource-conservative species, whereas decomposer activity is expected to increase, due to the establishment of decomposer populations and their response to local vegetation (“home-field advantage”, HFA). To date, the combined effect of these processes remains poorly understood. We studied 27 seminatural grasslands in western France, ranging from 1 to 25 years since last cultivation. We measured the functional composition of plant communities using litter traits (specific leaf area, leaf dry matter content, C/N ratio, phenolics), characterized the entire community of decomposers (macrofauna, mesofauna, microbes) and performed reciprocal litter transplants to quantify HFA. We found that, overall, decomposition was rapid, and HFA was not evident. While there was substantial among-grassland variation in decomposition and HFA, neither changed with grassland age. Litter quality and decomposer efficiency also remained, overall, unchanged. However, grassland age determined all measured litter traits and caused soil microbial C/N ratio to decline. Although these changes impacted decomposition individually, together they canceled out each other, resulting in constant decomposition across the chronosequence. Our results suggest that processes driving decomposition differ during grassland succession and suggest that HFA may be lower in communities with high litter quality. Moreover, simultaneous assembly processes have opposing and therefore stabilizing effects on decomposition, possibly explaining the outstanding resilience of primary production in temperate grassland ecosystems.
To understand how earthworms could improve soil porosity in no-tillage organic farming systems, the aim of our study was to compare the effect of different tillage systems on earthworm populations, ...from conventional (traditional mouldboard ploughing, MP and shallow mouldboard ploughing, SMP) to conservation tillage (reduced tillage, RT, direct drilling or very superficial tillage, NT) in three organic arable systems in France (sites A–C). In a second stage, the effect of earthworm activity on soil porosity under the four tillage systems was assessed at sites A and B. Earthworm abundance, biomass and diversity were measured over a 2–3-year period at the 3 sites. During the same period, soil structure (soil profile description and soil bulk density) and open worm burrows in the soil were assessed at sites A and B. After 3 years of experiments, it was found that at 2 sites earthworm abundance and biomass were higher in NT than with ploughing or reduced tillage. The increase of earthworms in NT is mainly due to anecic species increase. Earthworm abundance and biomass tend to decrease regardless of the tillage techniques employed at sites with a ley, and conversely, tend to increase in NT and RT at sites initially ploughed. In the short term, the increase of anecic species in NT has no effect on soil porosity evolution: NT soils were more compacted than those which were ploughed. A long-term experiment is required to assess the effect of biological activity on the physical components of soil in organic farming.
Vermifiltration is a new technology using earthworms to process organically polluted water. A pilot associated with a swine facility (piggery) with 66 swine was developed to treat diluted manure, ...produce earthworms and vermicompost, and reduce air pollution. The aim of the experiment reported here was to devise an integrated method – biological, chemical and physical – for further research and development of vermifiltration in diluted swine manure, and provide some preliminary results. The earthworm population increased by 30% in 4 weeks, indicating the acclimation of the earthworms. A reduction in ammonia emission was observed of about 50% for the whole system. Higher water (+100%), carbon (+70%), and total nitrogen (+80%) gaseous losses were observed compared to conventional breeding on a slatted floor. This methodology can be used for further studies to develop vermifiltration for earthworm and vermicompost production from diluted animal manure, without pollution transfer.
To link earthworm burrow distribution with the spatial variability of soil functions, accurate mapping of their spatial burrowing patterns is required. Eight natural soil cores (25
cm in diameter; up ...to 60
cm long) were collected from a pasture in spring 2001–2003. Earthworm populations were sampled on the first date and the anecic species
Nicodrilus giardi was found to be dominant (55% of the average density of 101 worms
m
−2). Soil cores were imaged using medical X-ray tomography equipment. These tomography images served as a basis for 3D reconstructions generated using specifically written software. Finally, the reconstructed burrow systems were measured and analysed using mathematical morphological approaches. The 3D reconstructions thus derived showed dense systems of interconnected burrows. A number of burrows extending vertically from the top to the bottom of the cores, but most were short, disconnected burrows. These two classes of burrows could not be linked with the activity of a particular species. In addition to the visual appraisal of the burrow system shape, structural parameters such as burrow volume, burrow wall surface area, burrow length density, topology and burrow angles were computed from the 3D reconstructions. Total burrow length density ranged from 687 to 1212
m
m
−3. Burrow volume density represented less than 2.5% of total soil volume and ranged from 13.3
×
10
3 to 24.2
×
10
3
cm
3
m
−3. Inspite of the apparently high continuity of burrows, only 9–43% of the volume was connected to the soil surface. Total burrow wall area ranged from 7721 to 12764
cm
2
m
−3 while surface-connected burrow wall surface area ranged from 1069 to 7237
cm
2
m
−3. The drilosphere volumes (i.e. a 2
mm thick sheath around burrows) were estimated to range from 44.9
×
10
3 to 52.9
×
10
3
cm
3
m
−3. Earthworm activity was found to vary throughout the year as revealed by changes in burrowing patterns. The burrow systems in spring 2001 were denser than that in others years, and the burrow systems in spring 2003 appeared to be partially re-filled close to the surface. This temporal variability demonstrates that it is virtually impossible to obtain true replicates of burrow systems of a given earthworm community without knowing (1) which burrows were created by which species and (2) the burrows age. However, the accurate description and quantification of earthworm burrow systems using powerful image processing tools allows a detailed discussion of the potential impact of earthworms on soil functions under natural conditions.
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