Using nematodes in soil ecotoxicology

Nematodes represent a very abundant group of soil organisms and non-parasitic species are important for soil quality and in the soil food web. In recent years, it has been shown that nematodes are appropriate bioindicators of soil condition and they are also suitable organisms for laboratory toxicity testing. The aims of this paper are to overview and critically assess methods and approaches for researching soil nematode ecotoxicology. In natural ecosystems, nematode abundance and community structure analyses were proved to be sensitive indicators of stress caused by soil pollutants and ecological disturbance. Community structure analyses may be approached from a functional or ecological point of view; species are divided into groups according to their feeding habits or alternatively the maturity index is calculated according to their ecological strategy. Many environmental factors have the potential to affect nematode community, which consequently results in high space and time variability. This variance is major handicap in field ecotoxicological studies because pollutant-nematode relationships are obscured. For prospective risk assessment of chemicals, several toxicity tests with nematodes were developed and are increasingly used. Sensitivity of these tests is comparable to tests with other soil species (e.g. enchytraeids, earthworms and springtails) while tests are less demanding to space and time. Most studies have focused on metal toxicity but organic compounds are almost overlooked. Endpoints used in tests were often mortality, reproduction or movement, but more sublethal endpoints such as feeding or biomarkers have been used recently too. Although there is an increasing amount of knowledge in soil nematode ecotoxicology, there is still a lot of various issues in this topic to research.     

Soil microbiocenosis as an indicator of stability of meadow communities in the environment polluted with heavy metals

The soil microbiota, a key component of natural ecosystems, is considered as a factor determining the stability of meadow communities. The diversity and abundance of the main ecologically significant groups of microorganisms in meadow soils have been studied along a gradient of long-term soil pollution with heavy metals in the Middle Urals. The results provide evidence for stability of the microbial assemblage formed in these soils. It has been found that the functional activity of certain physiological groups of microorganisms (nitrogen-fixing, denitrifying, and cellulolytic bacteria) and the respiratory activity of microbial communities are stimulated under conditions of heavy-metal soil pollution. Probable effects of the observed changes on mineralization of plant remains in meadow communities are discussed.     

The Role of Micromycetes in the Phytotoxicity of Crude Oil-Polluted Soils

The microbe–plant interaction in soil under crude oil pollution was studied in Perm oblast, the Cisural Region. In the rhizosphere of plants growing in the oil-polluted soil, an increased abundance of nonsymbiotic saprotrophic micromycetes was recorded. Under conditions of crude oil pollution, the development of these microorganisms in the rhizosphere proved to have a strong adverse effect on the plants due to production of mycotoxins.     

Initial Stages of Recovery of Soil Macrofauna Communities after Reduction of Emissions from a Copper Smelter

Analysis of natural recovery of communities after reduction of industrial emissions is important for gaining an insight into their stability. However, there is obvious deficit in observations on the course of this recovery; in particular, no data on direct comparisons of the state of communities before and after reduction of emissions are available for soil macroinvertebrates. We have studied the structure of soil macrofauna communities at the level of supraspecific taxa in southern taiga spruce-fir forests in the region exposed to emissions from the Middle Ural Copper Smelter (MUCS; Revda, Sverdlovsk oblast). The data over three periods—high, reduced, and almost terminated emissions (1990–1991, 2004, and 2014–2016, respectively)—have been compared to test the hypothesis that the communities do not recover rapidly. The results partly confirm this hypothesis. On the one hand, the response of pedobionts to pollution at a qualitative level has remained basically unchanged: in each of the three periods, their total abundance (and that of the majority of groups) decreased abruptly as the MUCS was approached, with dominance shifting from saprophages to phyto- and zoophages. On the other hand, signs of recovery have appeared during the last period: the abundance of pedobionts has increased, and pollution-sensitive groups (earthworms, enchytraeids, and mollusks) have approached closer to the MUCS. This is most likely explained by decrease in the toxicity of metals due to normalization of soil pH. Rapid recolonization of defaunated territory may be accounted for by the presence in it of microsites with more favorable conditions, compared to the surrounding area, which allow low-mobile forms to survive beyond the boundaries of their main distribution area.

     

Composition and abundance of soil macrofauna in pasture ecosystems of the steppe zone of the Urals

Changes in the abundance and species compositions of the main groups of soil invertebrates have been analyzed in ecosystems long used as pastures and exposed to different degrees of grazing. The sum of the results makes it possible to conclude that the zoological method of indication of pasture ecosystems can be used in ecological monitoring of steppe landscapes.     

Condition of the Soil Fauna near the Epicenter of an Underground Nuclear Explosion in the Northern Urals

Radioactive contamination affects soil organisms and causes profound structural rearrangements in soil zoocenoses, which are manifested in the decreased species diversity of invertebrate communities and low relative abundance of large soil invertebrates. However, these communities gradually recover their initial structure. The soil biota near the epicenter of an underground nuclear explosion performed 30 years ago in Perm oblast has been studied to reveal specific structural features of the soil macro- and microfauna. Its structural diversity is considered with regard to such components as species (taxonomic) composition, the structure of dominance, and the ratio of ecological and trophic groups.__________Translated from Ekologiya, No. 3, 2005, pp. 171–179.Original Russian Text Copyright © 2005 by Kolesnikova, Taskaeva, Krivolutskii, Taskaev.     

Effect of phytoremediation in technogenic landscapes of mining areas on the functioning of actinomycete communities

It has been shown that conditions formed in technozems of tailing dumps covered with a layer of chernozem are optimal for the development of soil microflora, including actinomycetes, as follows from their high abundance. The use of Leymus sabulosus (Bieb.) Tzvel in biological remediation of technozems formed in tailing dumps ensures an increase not only in the abundance of microorganisms in edaphotopes but also in their ecological diversity, compared to technozems planted with Rhus hirta (L.) Sudw, as confirmed by 1.2- and 1.9-fold increase in the Margalef and Berger–Parker diversity indices. Therefore, applying a layer of chernozem on technozems of tailing dumps provides for more efficient remediation of technogenic soils.     

不同农地整治措施对土壤细菌多样性的影响

为了研究不同农地整治措施对土壤细菌的影响,通过高通量测序技术,对不同农地整治措施下土壤细菌多样性与种群结构进行对比分析。结果表明:(1)从细菌多样性来看,实施农地整治的样点土壤细菌多样性显著提高;(2)从细菌种群结构来看,实施田块归并、平整土地、筑造沟渠以及土壤培肥等措施有效提高了甲基暖菌属(Methylocaldum)、亚硝化单胞菌(Nitrosomonas)、脱硫线菌属(Desulfonema)等有益菌属的丰度;(3)通过与土壤环境因子的相关性分析,酸碱度、铜和铅含量是影响农地整治区土壤细菌多样性与结构的重要因素。该研究证实了农地整治对提高土壤细菌多样性和改善土壤质量的重要作用,也为农地整治工作的开展提供了科学依据。     

Fluxes of dissolved organic matter in larch forests in the cryolithozone of central Siberia

Fluxes of dissolved organic matter (DOM) in larch biogeocenoses and its export from the drainage basin have been studied in the zone of continuous permafrost. A comparative assessment of DOM input into the soil has been made on slopes of northern and southern exposures (as variants reflecting the current state and warming). The dynamics of DOM export in a creek depending on the increasing depth of the active soil horizon in the drainage area have been revealed. It is concluded that an increase in the depth of the seasonally thawing layer induced by global warming will not have any significant effect on the amount of annual DOM export. Reduction of DOM export may be expected upon a decrease in litter stocks under the effect of their mineralization and forest fires.     

The ecology of the red fox (<Emphasis Type="Italic">Vulpes vulpes</Emphasis> L.) in the middle Lena River basin

The population of foxes in the central regions of Yakutia has grown by a factor of four to five during the period from 2000 to 2011–2012, following an increase in the abundance of voles from the genus Microtus. A total of 130 carcasses of foxes taken in 2007–2012 have been examined. Age- and sex-related variation in morphological features has been described. The demographic structure of the population has been studied by estimating animal age from annual layers in the recording structures. Changes in female fertility and involvement in reproduction depending on age and feeding conditions have been analyzed. Changes in the composition of fox diet caused by long-term population depression in the mountain hare and their effect on the dynamics of fox abundance have been revealed. Age- and sex-related characteristics of the condition factor in foxes and sex-related differences in their dietary preferences have been demonstrated.     

Changes in the assemblage of necrophilous invertebrates under the effect of pollution with emissions from the Middle Ural Copper Smelter

Changes in the abundance and taxonomic and trophic structure of necrophilous invertebrates inhabiting mixed forests have been studied in the area polluted with the emissions from the Middle Ural Copper Smelter. It has been shown that the abundance of most taxa decreases by factors of 2 to 80 along the pollution gradient, but the trophic structure and composition of major groups vary insignificantly. Changes in the necrophilous assemblage can be caused by either direct (toxic) action of industrial pollutants or their indirect effect exerted through modification of habitats.     

Effects of seven organic pollutants on soil nematode Caenorhabditis elegans

Caenorhabditis elegans is a free-living soil nematode that is commonly used as a model for toxicity tests. The aim of this study was to investigate the toxicity of seven organic pollutants: four azaarenes (quinoline, acridine, phenazine, and 1,10-phenanthroline), short-chain chlorinated paraffins, and two organochlorinated pesticides (toxaphene and hexachlorobenzene). The exposure to all chemicals was carried out in three test media (soil, agar, and aquatic medium), and adult mortality was evaluated after 24 and 48 h. Toxaphene was the most toxic substance with LC(50) (48 h) of 379 mg/kg in the soil and 0.2 mg/L in the aquatic medium. Quinoline was the most toxic chemical in agar test with LC(50) (48 h) of 10 mg/L. HCB showed a very low toxicity in all tests, maybe due to its very low water solubility. Longer than 24-h test duration was found necessary for getting more correct data on toxicity. In comparison with other studies, C. elegans was less sensitive than other soil invertebrates. Different response might be attributed to different exposure routes and shorter test duration. Equilibrium partitioning theory was used to calculate K(oc) from results of soil and aquatic tests but this approach was found not working. Our results suggest that the tests with nematode C. elegans should be included to the battery of tests for risk assessment of POPs in soil.     

Changes in the taxonomic structure of herpetobiont arachnids along the gradient of pollution with emissions from a copper smelter

Changes in the dynamic density of herpetobiont arachnids and the ratio of spider life forms have been studied in southern taiga forests transformed under the impact of emissions from a copper smelter. Along the pollution gradient, the dynamic density of spiders decreases; web-spinning spiders are replaced by ambush spiders, since the abundance of families Lycosidae and Gnaphosidae increases while that of the family Linyphiidae decreases; and spatial variation in the abundance of arachnids increases. One harvestmen family (Nemastomatidae) completely disappears near the copper smelter.     

Paleosols of the Solonchanka IX site and climate of the Transural steppe zone in the fourth century AD

Studies on paleosols under an archaeological landmark of a rare type (a complex of kurgans with “whiskers”) dating from the Early Iron Age (the fourth century AD) have been performed in the steppe zone of the Transural Plateau. The size and shape of third-order soil polygons under stony ridges (“whiskers”) between the kurgans have been described in detail. The results have shown that the paleosol under the kurgans erected at the turn of the Late Sarmatian and Hun times (1600 years ago) is characterized by a higher humus content and deeper location of the carbonate horizon, compared to the recent soil. This indicates that an increase in atmospheric humidity took place in the fourth century AD.     

Differences in responses of herpetobionts and geobionts to impact from the Kosogorsky Metallurgical Plant (Tula region,Russia)

The influence of the Kosogorsky Metallurgical Plant (KMP; Tula region, Russia) on the abundance and biodiversity of carabid beetles and soil macrofauna and on the trophic activity of soil biota was studied. Metal concentrations in the impact plot were many times higher than those in the control plot located on the same transect. As the transect approached KMP, both the abundance of soil invertebrates (geobionts) and trophic activity of the soil biota remained unchanged, whereas the abundance and diversity of carabids (herpetobionts) decreased drastically. It is suggested that the impact of the KMP on herpetobionts is accounted for by modification of the structure of ecosystems and that herpetobiontic and geobiontic groups of the macrofauna respond differently to this impact because of differences in the ecological mechanisms of population response.     

覆盖对南方红壤桔园生态系统的影响

连续４年观测了几种覆盖处理下红壤坡地桔园内气温、土温、土壤水分状况，土壤养分及土壤物理性状的差异，分析了造成这些差异的直接原因，提出地膜加草覆盖是南方红壤无灌溉条件坡地桔园最理想的覆盖方式之一。     

Enchytraeid Community (Annelida,Clitellata, Enchytraeidae) and Its Dependence on Edaphic Conditions in Rice Agroecosystems in Russia

Russian Journal of Ecology - Communities of soil animals (meso- and macrofauna) in rice paddies tend to be fragmented, and have extremely low abundance. Nevertheless, some groups, such as...     

An overview of BORIS: Bioavailability of Radionuclides in Soils

The ability to predict the consequences of an accidental release of radionuclides relies mainly on the level of understanding of the mechanisms involved in radionuclide interactions with different components of agricultural and natural ecosystems and their formalisation into predictive models. Numerous studies and databases on contaminated agricultural and natural areas have been obtained, but their use to enhance our prediction ability has been largely limited by their unresolved variability. Such variability seems to stem from incomplete knowledge about radionuclide interactions with the soil matrix, soil moisture, and biological elements in the soil and additional pollutants, which may be found in such soils. In the 5th European Framework Programme entitled Bioavailability of Radionuclides in Soils (BORIS), we investigated the role of the abiotic (soil components and soil structure) and biological elements (organic compounds, plants, mycorrhiza, and microbes) in radionuclide sorption/desorption in soils and radionuclide uptake/release by plants. Because of the importance of their radioisotopes, the bioavailability of three elements, caesium, strontium, and technetium has been followed. The role of one additional non-radioactive pollutant (copper) has been scrutinised in some cases. Role of microorganisms (e.g., K(d) for caesium and strontium in organic soils is much greater in the presence of microorganisms than in their absence), plant physiology (e.g., changes in plant physiology affect radionuclide uptake by plants), and the presence of mycorrhizal fungi (e.g., interferes with the uptake of radionuclides by plants) have been demonstrated. Knowledge acquired from these experiments has been incorporated into two mechanistic models CHEMFAST and BIORUR, specifically modelling radionuclide sorption/desorption from soil matrices and radionuclide uptake by/release from plants. These mechanistic models have been incorporated into an assessment model to enhance its prediction ability by introducing the concept of bioavailability factor for radionuclides.     

Long-term field application of sewage sludge increases the abundance of antibiotic resistance genes in soil

Sewage sludge and manure are common soil amendments in crop production; however, their impact on the abundance and diversity of the antibiotic resistome in soil remains elusive. In this study, by using high-throughput sequencing and high-throughput quantitative PCR, the patterns of bacterial community and antibiotic resistance genes (ARGs) in a long-term field experiment were investigated to gain insights into these impacts. A total of 130 unique ARGs and 5 mobile genetic elements (MGEs) were detected and the long-term application of sewage sludge and chicken manure significantly increased the abundance and diversity of ARGs in the soil. Genes conferring resistance to beta-lactams, tetracyclines, and multiple drugs were dominant in the samples. Sewage sludge or chicken manure applications caused significant enrichment of 108 unique ARGs and MGEs with a maximum enrichment of up to 3845 folds for mexF. The enrichment of MGEs suggested that the application of sewage sludge or manure may accelerate the dissemination of ARGs in soil through horizontal gene transfer (HGT). Based on the co-occurrence pattern of ARGs subtypes revealed by network analysis, aacC, oprD and mphA-02, were proposed to be potential indicators for quantitative estimation of the co-occurring ARGs subtypes abundance by power functions. The application of sewage sludge and manure resulted in significant increase of bacterial diversity in soil, Proteobacteria, Acidobacteria, Actinobacteria and Chloroflexi were the dominant phyla (> 10% in each sample). Five bacterial phyla (Chloroflexi, Planctomycetes, Firmicutes, Gemmatimonadetes and Bacteroidetes) were found to be significantly correlated with the ARGs in soil. Mantel test and variation partitioning analysis (VPA) suggested that bacterial community shifts, rather than MGEs, is the major driver shaping the antibiotic resistome. Additionally, the co-occurrence pattern between ARGs and microbial taxa revealed by network analysis indicated that four bacterial families might be potential hosts of ARGs. These results may shed light on the mechanism underlining the effects of amendments of sewage sludge or manure on the occurrence and dissemination of ARGs in soil.