Beetles community structures under different reclamation practices

Differences in beetle community structures between not re-cultivated over 60 years old forest and 10 years old re-cultivated meadow and shrubs were compared. On each locality there were arranged three replicates of 10 pitfall trap rows. Mean abundance of beetles was significantly greater on old forest stand than re-cultivated meadow. However no significant differences between localities in species richness and non parametric index of diversity (Shannon H′) were recorded. Rank–abundance curves for newly established communities best fits to geometric model of distribution (r = 0.98, P < 0.001) which is characteristic for species poor communities, where a single environmental resource is extremely important, meanwhile old stand, without any reclamation practice is best fitted to lognormal distribution model (r = 0.99, P < 0.001) which is typical for more stable and well developed communities. Principal component analysis for log (N + 1) transformed matrix of abundances described well 60% of the total variance. Two clear groups of species transects were derived: one concentrated assemblages of both reclaimed and newly established communities and the second one old non reclaimed forest stands. Significant feature of trophic guild structure in all three communities is the lowest abundance of decomposers meanwhile predators predominate on non re-cultivated old sites and herbivores on reclaimed young stands.     

Factors influencing earthworm communities in post-industrial areas of Krakow Soda Works

Application of earthworm in soil re-cultivation and re-creation in post-industrial ecosystems make a big challenge for temporal applied zoology. The sediments of the Krakow Soda Works “Solvay” have undergone land reclamation in different ways: older sediments traps were left without any re-cultivation practices; meanwhile the newest ones were reclaimed using standard method (new soil cover planted with combination of grass and leguminous plants). The effect of different treatments on community and population structure of earthworm was estimated during consecutive years 1999–2000. Six localities differing in time of establishment, reclamation processes, vegetation type and soil properties were chosen. Nine species were recorded, among which Aporrectodea caliginosa occurred in all localities, being also the most abundant. Two other species, Lumbricus rubellus and Dendrobaena octaedra, which are epigeic species, become most important in forest assemblages and were characteristic for communities of older succession processes. Abundance of adult forms as well as total biomass were significantly affected by soil depth (r = 0.75, P < 0.05, r = 0.917, P < 0.001, respectively). Species richness however was connected with higher amount of macroelements and average plant height. Shannon diversity index and its evenness negatively correlated only with forestation (r = –0.67, P < 0.05, r = –0.68, P < 0.05, respectively). Niche overlap (α Pianka) for all analysed species extracted two groups differing in environmental requirements. First contained epigeic earthworms, closely related to plant succession (PCA results), the other one grouped endogeic and anecique species correlated significantly with soil depth and plant density. Community structure of earthworms do not reflects succession changes in post-industrial habitats, but is strongly affected by microhabitat factors in local scale (mainly soil depth and plant density).     

Succession of soil nematodes in pine forests on coal-mining sands near Cottbus,Germany

The succession of soil nematodes from initial planting with Pinus sylvestris seedling to about 30-year-old pine plantations on coal mining sands in the Lusatian lignite-mining district near Cottbus (Germany) was studied and compared with the nematode fauna of a 40-year-old semi-natural pine forest on naturally formed sandy soil. The initial stage was primarily characterised by a very low abundance (20×10³ individuals/m²), which increased over a period of two years to values common in older pine plantations (500–600×10³ individuals/m²). In the semi-natural forest the mean abundance of nematodes was about 1300×10³ individuals/m². Populations of Tardigrada, Rotifera and Enchytraeidae also increased with stand age. Nematode biomass increased from 49 to 543 mg m⁻² in pine plantations and slightly decreased in the semi-natural forest to 301 mg m⁻² over the period of investigation. The early colonisation of the initial stage was by bacterivorous (Acrobeloides) and fungal feeding (Aphelenchoides) nematodes, but the communities diversified as succession progressed with bacterivorous nematodes of the genera Plectus, Wilsonema and Metateratocephalus, root-fungal feeding Filenchus, omnivorous Aporcelaimellus and Eudorylaimus, and predacious Prionchulus becoming abundant. The abundance of plant-parasitic nematodes was very low. The greatest number of nematode genera was found in the semi-natural forest.     

An outline of soil nematode succession on abandoned fields in South Bohemia

Secondary succession of nematodes was studied in 1–48-year-old abandoned fields on cambisols in South Bohemia, Czech Republic, and compared with cultivated field and sub-climax oak forests. Bacterivores were the predominant group in the cultivated field whereas in forests root-fungal feeders (mainly Filenchus) were almost as abundant as bacterivores. The total abundance of nematodes in the cultivated field averaged 868 × 10³ ind m⁻². During the first three years of succession the abundance practically did not change (775 × 10³ ind m⁻²), the fauna was still similar to that in cultivated field but the biomass increased mainly due to Aporcelaimellus. Then the abundance increased up to 3731 × 10³ ind m⁻² in 7–8-year-old abandoned fields, plant parasites (Helicotylenchus) dominated and the fungal-based decomposition channel was activated. Later the abundance stabilised at between 1086 and 1478 × 10³ ind m⁻² in 13–25-year-old successional meadow stages with high population densities of omnivores and predators. The total abundance of nematodes was low in the 12–13-year-old willow shrub stage (594 × 10³ ind m⁻²), increased in the 35–48-year-old birch shrub stage (1760 × 10³ ind m⁻²) and the nematode fauna developed towards a forest community. The diversity and maturity of nematode communities generally increased with the age of abandoned fields but the highest values were in meadow stages (81–113 species, 57–68 genera, MI 2.73–3.30). The development of meadow arrested succession towards forests or diverted succession towards a waterlogged ecosystem. The succession of nematodes was influenced by the method of field abandonment (bare soil vs. legume cover, mowing) that affected the formation of either a shrub or meadow stage, and by the soil water status. The composition of the nematode fauna indicated that the soil food web could recover faster from agricultural disturbance under successive meadows than under shrubs.     

Responses of soil nematode community structure to different long-term fertilizer strategies in the soybean phase of a soybean–wheat–corn rotation

The impact of long-term application of fertilizers in soybean fields on soil nematode community structure was studied. The long-term application model of fertilizers lasted 13 years in a soybean–wheat–corn rotation, and included three treatments: no fertilizer (NF), chemical fertilizer (urea and ammonium phosphate, CF), and pig manure combined with chemical fertilizer (MCF). The soil nematode community structures and ecological indices were determined from soil samples taken at five soybean growth stages from May to October in the soybean phase of the rotation. Fertilizer application had significant effects on abundance of plant parasites, bacterivores and fungivores (P < 0.05), but had no significant effects on total nematodes and omnivores-predators. Abundance of plant parasites was higher in NF than in MCF and CF, and abundance of bacterivores was highest in MCF. Fertilizer application significantly affected Plant-parasitic Nematode Maturity Index (PPI) and Nematode Channel Ratio (NCR) ecological indices (P < 0.05). Shannon–Weaver Index (H′) and Species Richness (SR) indices were higher in MCF than in either NF or CF. The abundances of total nematode and plant parasites showed increasing trend with soybean growth in all three treatments. This is probably due to soil environment being more suitable for soil nematode survival with more food available for plant parasites as the soybean grows. Soybean growth stage significantly affected the H′, Free Living Nematode Maturity Index (MI) and PPI. Bacterivores significantly correlated with soil nutrient status suggesting that they could be used as a potential indicator of soil fertility.     

Diversity and distribution of nematode communities in grasslands from Romania in relation to vegetation and soil characteristics

The nematode communities of 36 grassland ecosystems in Romania, belonging to different plant associations and soil types, were studied. The abundance of nematodes, the species and trophic types present, as well as their distribution in relation to plant community and soil characteristics are analyzed and discussed.The abundance of nematodes from the 36 grasslands studied ranged between 0.41 × 10⁶ and 8.57 × 10⁶ individuals/m², and a total of 121 genera and 145 species of nematodes were found. The highest diversity was found in grasslands developed on brown earth soil (65–67 genera and 74–76 species), with least diversity in those evolving on podzol and lithosol (33–36 genera with 25–28 identified species). Most of the dominant taxa were found in specific soil layers; some obligate plant parasitic genera (e.g., Paratylenchus, Rotylenchus, Criconema) showed preference for deeper soil layers. The nematode diversity index (H′), with values ranging between 2.38 and 3.47, did not differ significantly between the different types of grasslands. Plant feeding, bacterial feeding, hyphal feeding and omnivorous nematodes were the main groups in mountainous grasslands developed on different soil types. Plant feeding and bacterial feeding nematodes dominated the trophic structure and more plant feeders (62–69%) were found in communities of subalpine and alpine grasslands developed on podzol and alpine meadow soil, than in those developed on rendzina and lithosol (27–33%). The ratio of hyphal feeding to bacterial feeding nematodes (Hf/Bf) is constantly in favour of the bacterial feeding group, the values being an indicator of good soil fertility for most studied grasslands. The nematode communities of grasslands are grouped into six main clusters according to their genera affinity and distinguished by different grassland and soil types. Communities from subalpine grasslands developed on rendzina, acid brown and lithosol have the greatest similarities. An ordination of nematode communities in relation to important environmental variables is presented. Environmental variables relevant in explaining the patterns of nematode composition in grasslands, using canonical correspondence analysis (CCA), are: humus, pH, total nitrogen, exchangeable bases and soil type. No single factor could be selected.     

Influence of organic Crotalaria juncea hay and ammonium nitrate fertilizers on soil nematode communities

Comparisons of organic and inorganic fertilizer effects on nematode communities depend on the specific organic fertilizer used. Field experiments were conducted during 2001 and 2002 in a squash (Cucurbita pepo) agroecosystem to determine if applying sunn hemp (Crotalaria juncea) hay as an organic fertilizer improved nematode communities involved in soil nutrient cycling compared to an equivalent N rate (100 kg N/ha) of ammonium nitrate. Fertilizer source had minimal effect on nematode communities in 2001 when treatments were applied after a winter cover crop of oats (Avena sativa), but differences (P ≤ 0.05) between the fertilizer sources occurred in 2002 when no winter cover cropping preceded squash. Fertilization with sunn hemp hay increased abundance of the bacterivore guilds Ba₁ and Ba₂, and increased fungivores at the end of the experiment. Compared to ammonium nitrate, fertilization with sunn hemp hay resulted in a community with lower maturity index, higher enrichment index, and lower channel index, consistent with a disturbed and nutrient-enriched soil food web undergoing bacterial decomposition. Sunn hemp hay occasionally stimulated omnivorous nematodes, but suppressed plant-parasitic nematodes relative to ammonium nitrate fertilizer. Increasing the sunn hemp hay rate to 200 kg N/ha increased the abundance of bacterivores, fungivores, and predatory nematodes, and total nematode abundance compared to hay at 100 kg N/ha. Fertilization with ammonium nitrate increased the percentage of herbivores, but reduced percentage and abundance of omnivores. In conclusion, sunn hemp fertilizer maintained greater numbers of nematodes involved in nutrient cycling as compared to ammonium nitrate.     

Effect of subsurface clay on nematode communities in a sandy soil

A variety of soil properties can directly or indirectly affect nematode community structure. The effects of subsurface clay content (at 20–40 cm depth) on nematodes in the surface layer (0–20 cm depth) of a sandy soil were examined in field experiments in Florida, USA. Plots were established in a site with a relatively uniform sandy upper soil layer (88–91% sand and 5–7% clay at 0–20 cm depth) but with varying levels of clay in the subsurface layer (3–35% clay at 20–40 cm depth). Nematode numbers in the surface soil layer were affected by the amount of clay in the subsurface layer. Population densities of a number of different nematode genera were greater in the surface layer of plots with 35% subsurface clay than in plots with 3% subsurface clay. Indices of nematode community structure were largely unaffected, since effects of subsurface clay were observed across all nematode groups. Most nematodes (70–80% of total numbers) occurred at 0–20 cm depth, although Teratocephalus was more common at 20–40 than at 0–20 cm. Subsurface clay content indirectly affected soil moisture and other environmental factors in the upper soil layer in which most nematodes reside.     

Nematode dispersion by runoff water: Case study of Radopholus similis (Cobb) Thorne on nitisol under humid tropical conditions

To minimize application of nematicides in banana fields, crop systems have been developed in the French West Indies that combine fallow or rotation crops and nematode-free in vitro plants. After two to four years, populations of the burrowing nematode Radopholus similis have developed enough to cause economic losses, leading banana growers to use nematicides. To understand how banana fields are recontaminated, we studied the dissemination of R. similis by water flow. At a 1-m scale, we analyzed the dispersion of R. similis under a rainfall simulator: we isolated a 1-m² study plot, placed a R. similis suspension on the upstream soil surface, and simulated a 60 mm/h rainfall for 72 min. We collected soil samples every 10 cm downstream after 12 min of rainfall, and subsequently at 20-min intervals, and extracted the nematodes using a Seinhorst elutriator and then a Baermann funnel. Our results showed that the nematode dissemination follows an inverse exponential law, and depends more on soil moisture at the beginning of rainfall than on the length of rainfall: in fresh soil, 69–80% of the R. similis recovered were found less than 10 cm downstream from the nematode inoculation line, whereas in wetted soil, 76–85% of the recovered individuals were collected in the outlet tub located downstream from the apparatus. This passive dissemination model partially explains the distance covered by individual nematodes but not the low percentage of motile nematodes recovered in the outlet tub (10% and 36% in fresh and wet soils) compared to the percentage of motile nematodes found in the soil (80% and 84% in fresh and wet soils). Indeed, water runoff is likely to disseminate R. similis over long distances only when soil moisture is close to field capacity.     

Effect of nitrogen and phosphate fertilisers on microbial and nematode diversity in pasture soils

Soil microbial and nematode populations, soil microbial community structure, and microbial and nematode functional diversity were studied in two fertiliser trials on perennial pasture at three sampling times. The N trial involved the application of 0, 200 and 400 kg N ha⁻¹ y⁻¹ in the form of urea. The P trial involved the application of 0, 30, 50 and 100 kg P ha⁻¹ y⁻¹ as superphosphate. The purpose of this study was to determine biological characteristics that may be used as indicators of soil quality as affected by fertiliser inputs.The N or P treatments had no effect on total bacteria, cellulolytic microbes, or the fluorescein diacetate hydrolysis. The fungus Fusarium culmorum was found only in the 200 kg N treatment (P<0.01). Gliocladium roseum declined in isolation frequency with increasing N (P<0.05,) while other Gliocladium spp. increased (P<0.01).The microbial community structure, ecophysiological index (EP), and colony-development index (CD) were determined using: colony development rates in 1/10 tryptose soy agar (TSA), a Pseudomonas medium, and a nutrient poor medium. These parameters were not affected by the addition of the N or P fertilisers. In the N trial, the functional diversity of soil microbes, as determined by Shannon Diversity Index (H) and average well colour development (AWCD) (using Biolog gram negative microplates) was higher in the unfertilised than fertilised treatments. The values for H and AWCD were 4.2 and 0.78 in the unfertilised compared to 4.0 and 0.53 in fertilised treatment (P<0.01, 48 h, mean for both N treatments), respectively. There were no significant differences in these values in the P trial.Populations of the plant feeding nematodes Pratylenchus and Paratylenchus were greater (P<0.05) whereas those of Meloidogyne were lower (P<0.001), in soils fertilsed with N than in unfertilised soils. The genera Aporcelaimus, Dorylaimellus, and Tylencholaimellus were found only in control plots and their loss paralleled faunal changes resulting from pasture improvement reported elsewhere. Nematode Maturity Index (MI) values were 1.78, 1.85, and 1.53 for the N fertiliser treatments (P<0.05) suggesting a reduction at 400 kg N. The MI was not affected by the application of P (mean, 2.01), however, but all values in the P trial were greater than in the N trial. In the N and P trials an average of 29 and 35 nematode taxa were discriminated. The ratio of bacterial-feeding nematodes to bacterial-feeding plus fungal-feeding nematodes was similar across all treatments of the N (0.90–0.92) and P (0.84–0.90) trials, suggesting no relative change in the importance of bacterial- and fungal-mediated decomposition pathways in these soils as a result of fertiliser application.The finding that most microbiological characteristics did not respond to many years of fertiliser treatments suggests that the microbial community in the soils are similar and fertiliser amendments are insufficient to induce changes (either direct or indirect due to plant effects) in these communities. However, the consistent decrease in functional diversity of soil microflora and nematode populations with the application N, but not P, indicates that the N application can impact on community structure.     

Leaf litter is the main driver for changes in bacterial community structures in the rhizosphere of ash and beech

The rhizosphere and the surrounding soil harbor an enormous microbial diversity and a specific community structure, generated by the interaction between plant roots and soil bacteria. The aim of this study was to address the influences of tree species, tree species diversity and leaf litter on soil bacterial diversity and community composition. Therefore, mesocosm experiments using beech, ash, lime, maple and hornbeam were established in 2006, and sampled in October 2008 and June 2009. Mesocosms were planted with one, three or five different tree species and treated with or without litter overlay.Cluster analysis of DGGE-derived patterns revealed a clustering of 2008 sampled litter treatments in two separated clusters. The corresponding treatments sampled in 2009 showed separation in one cluster. PCA analysis based on the relative abundance of active proteobacterial classes and other phyla in beech and ash single-tree species mesocosm indicated an effect of sampling time and leaf litter on active bacterial community composition. The abundance of next-generation sequencing-derived sequences assigned to the Betaproteobacteria was higher in the litter treatments, indicating a higher activity, under these conditions. The Deltaproteobacteria, Nitrospira and Gemmatimonadetes showed an opposite trend and were more active in the mesocosms without litter. The abundance of alphaproteobacterial sequences was higher in mesocosms sampled in 2009 (P = 0.014), whereas the Acidobacteria were more active in 2008 (P = 0.014). At the family level, we found significant differences of the litter vs. non-litter treated group. Additionally, an impact of beech and ash as tree species on soil bacterial diversity was confirmed by the Shannon and Simpson indices. Our results suggest that leaf litter decomposition in pH-stable soils affect the soil bacterial composition, while tree species influence the soil bacterial diversity.     

Biogeophysical factors influencing soil respiration and mineral nitrogen content in an old field soil

Microbivorous grazers are thought to enhance nutrient mineralization. The predicted effect of microbivory on nutrient cycling depends on the pore habitat model used. We evaluated CO₂ evolution and mineral N content of an old field soil to test two alternative habitat hypotheses. The exclusion hypothesis predicts that nematodes are separated from their microbial food resources in water-filled pores when soils dry, resulting in slower rates of biogeochemical transformations. The enclosure hypothesis predicts that nematode densities increase relative to their forage in smaller, isolated water volumes when soils dry, accelerating rates of biogeochemical transformations. We investigated the effect of soil moisture on the relationship between microbial biomass, microbivorous and predaceous nematodes, soil respiration and mineral N concentrations in an old field five times during the course of a year.We could evaluate the validity of the two habitat hypotheses for the entire field only in August 1997 because that was the only sampling date when maximum water-filled pore diameters were smaller than microbivorous nematode body diameters in all sampled field locations. The mean microbivorous and predaceous nematode abundances for the field in August were greater than 6300 kg⁻¹ and 80,000 kg⁻¹, respectively. Accordingly, the exclusion hypothesis was rejected. Predaceous nematode abundance was markedly higher in August than at any other sampling date. The high abundance of predators present suggests that detrital resources were not limiting productivity and that predators and microbivores were in enclosures, allowing predators to efficiently access their prey. Spatial maps, in agreement with linear correlation analyses, suggest that under our driest sampling conditions, soil respiration and mineral N content were controlled by microbivory and predation.     

Dynamic changes of bacterial community under the influence of bacterial-feeding nematodes grazing in prometryne contaminated soil

Microcosm experiments were carried out to study the effects of bacterial-feeding nematodes and prometryne on soil bacterial communities in contaminated soil. Prometryne (5 or 10 mg kg⁻¹ dry soil, that is, P5 or P10) and bacterial-feeding nematodes (5 or 10 individuals g⁻¹ dry soil, that is, N5 or N10), singly and in combination (P5N5, P5N10, P10N5, P10N10), were added to a nematode-free soil. An uncontaminated nematode-free soil was studied for comparison (Control). Bacterial-feeding nematode grazing boosted soil enzyme activities in contaminated soils, thus speeding up prometryne degradation. In the initial stage of the experiment, prometryne enhanced the soil enzyme activities too, but served the opposite purpose later. Denaturing gradient gel electrophoresis (DGGE) analysis indicated that prometryne contamination and nematode grazing over the incubation period exerted an obvious impact on Species richness (S), Shannon–Wiener index (H′) and Evenness (E_H) of soil bacteria, which increased initially, then decreased and increased again later. The cluster analysis of DGGE profiles showed that the similarity of soil bacterial communities in all treatments with indigenous microbes, P5, P5N5, P5N10, P10, P10N5, and P10N10 and the Control was 75%, 44%, 78% and 49% at Day 0, Day 8, Day 18 and Day 30, respectively. Compared to the Control, DGGE profiles displayed a varying characteristic bands pattern in all treatments over the incubation period with certain bands present in the treatments while not in the Control and vice versa, suggesting that bacterial-feeding nematode grazing and prometryne contamination affected soil bacterial communities evidently. Consequently, when added to contaminated soil, bacterial-feeding nematodes can contribute to restoration of contaminated sites by degrading toxic compounds like prometryne through enhanced microbial activity.     

Molecular and physiological bacterial diversity of a semi-arid soil contaminated with different levels of formulated atrazine

A semi-arid soil treated with different concentrations of formulated atrazine in a laboratory experiment was studied over 45 days, by different biological and molecular parameters (bacterial enumeration (cfu), community level physiological profiles (CLPPs) measured by Biolog^® and denaturing gradient gel electrophoresis (DGGE)), to study the bacterial community diversity.Formulated atrazine was almost totally degraded at different concentrations after this incubation time. The number of colony forming units (cfu) for soils with 100 and 1000 mg kg⁻¹ atrazine was significantly (p ≤ 0.05) higher than for the control, 1 and 10 mg kg⁻¹ treatments. DGGE banding patterns showed that regardless of time elapsed, concentrations of 10, 100 and 1000 mg kg⁻¹ atrazine in soil, affected the bacterial community compared to control and 1 mg kg⁻¹.The Shannon diversity index (H′) based on CLPP data showed a significant (p ≤ 0.05) decrease at atrazine concentrations of 100 and 1000 mg kg⁻¹. The Shannon diversity indices for different guilds of source carbon and the parameters K and r (based on the kinetics of colour formation rather than on the degree of colour development) were related to guilds of carbon substrates and atrazine concentration at a sampling time. The parameter K was very sensitive to atrazine effects on microbial communities.These biological and molecular parameters can be used to monitor changes in soils treated with atrazine at different concentrations, even when the pesticide is degraded.     

Effects of land use changes on winter-active Collembola in Sanjiang Plain of China

Sanjiang Plain is the largest concentrated area of freshwater wetlands in China, however nearly 80% of these freshwater wetlands were drained or reclaimed in the past 50 years. It is important to know whether wetlands reclamation would affect soil invertebrates, especially the winter-active invertebrates. During November 2011 to April 2012, we used pitfall traps and in-field direct observation methods to study the activity of collembolans in wetland, and a reclaimed forest plantation and soybean field. In total, 3465 collembolans were captured and identified to 8 species from 6 families. Desoria sp. 1, Desoria sp. 2 and Desoria sp. 3 were the three dominant species. Collembolan abundance and assemblages were significantly affected by the land use changes. The results showed that (1) Collembola captured by pitfall traps showed a highest abundance in wetland, with ∼50% decreased abundance in soybean field, and ∼75% decreased in the forest plantation. (2) Collembola activity changed during the winter season, their activity significantly increased from early winter to late winter; with a peak in March in all three land use types. (3) Collembola assemblages were affected by land use changes with a significant decrease of frequency of Desoria sp. 3 and a significant increase of frequency of Desoria sp. 2 in soybean field and forest plantation. (4) Collembolan densities on the snow surface usually peaked between 1400 h and 1500 h, and decreased quickly when the temperature dropped below freezing. Mean abundance reached 119 individuals m⁻² on the snow surface in wetland, 152 individuals m⁻² in soybean field, and 64 individuals m⁻² in forest plantation. All collembolans moved up and down through the snow profile depending on temperature, no collembolans were found on the snow surface in the evening. Our study indicated that the reclamation of wetland resulted in a significant decrease of abundance and a different assemblage of winter active Collembola in Northeast China, but land use changes did not change their pattern of activity: Collembolans were rarely active in early and middle winter and mostly active in late winter. Their daily densities on the snow surface fluctuated according to both air temperatures and land use types.     

Impact on soil fauna of sheep faeces containing a range of parasite control agents

To compare the impact of parasite control agents in sheep faeces, 1 kg quantities of fresh faeces were spread uniformly over 1 m² pasture plots in June 2001 (winter; a time of high earthworm activity). Faecal treatments applied to five replicate plots were C− (none), C+ (from untreated sheep), B (from sheep with an intra-ruminal bolus releasing a benzimidazole anthelmintic—‘albendazole’), ML (from sheep with a bolus releasing a macrocyclic lactone anthelmintic—‘ivermectin’), F (from sheep receiving a daily feed supplement containing chlamydospores of the nematophagous fungus, Duddingtonia flagrans). The disappearance of faeces was assessed visually over the 50 days following faecal application, then soil samples were taken to assess: (a) populations of earthworms and other soil macrofauna, (b) nematodes and other soil microfauna, and (c) the presence of D. flagrans in soil. Faecal disappearance was greatest in F and C+ plots and least in ML and B plots at 12 and 23 days (P < 0.05). Earthworm casting after 23 and 50 days was greater (P < 0.05) in plots with faeces (C+, ML, F, but not B) than in plots without faeces (C−). Greater earthworm activity in plots with faeces was reflected in greater numbers of earthworms, cocoons and greater biomass m⁻² than in C− plots. On the basis of faecal dry weight applied, F plots had most earthworms and ML plots the least. After 50 days total nematodes in 0–5 cm soil showed a treatment effect (P < 0.001), being more abundant in F, C+ and B than in C− and ML plots; enchytraeids, rotifers, tardigrades and copepods showed no treatment effects. A few nematode taxa (Acrobeles, Alaimus, Pungentus, Tylencholaimus) showed significant treatment effects. The greatest effect among nematodes was in nematode channel ratio (NCR) (P < 0.008), with a decrease in F plots; changes in NCR may reflect the impact of earthworm activity on soil processes rather than a direct effect of the fungal treatment on nematodes. D. flagrans did not become established in the soil. During the trial conditions were favourable for earthworms and their activity was high in all treatments receiving faeces, with F and ML plots being the extremes. There was an apparent shift towards fungal-mediated decomposition in F plots. At the end of the 50-day trial, in a period when earthworms were active, there was no evidence of differential effects of any of the anthelmintic treatments on environmental indicators.     

Soil moisture effects on infectivity and persistence of the entomopathogenic nematodes Steinernema scarabaei,S. glaseri,Heterorhabditis zealandica,and H. bacteriophora

We tested the effect of soil moisture on the performance of four entomopathogenic nematodes species that have recently shown promise for the control of white grubs, i.e., Heterorhabditis bacteriophora, H. zealandica, Steinernema scarabaei, and S. glaseri. Experiments for all four nematodes were conducted in sandy loam, for S. scarabaei also in loamy sand and silt loam. Infectivity was tested by exposing third-instar Japanese beetle, Popillia japonica, to nematodes in laboratory experiments and determining nematode establishment in the larvae and larval mortality. Nematode infectivity was the highest at moderate soil moistures (−10 to −100 kPa), and tended to be lower in wet (−1 kPa) and moderately dry (−1000 kPa) soil. In dry soil (−3000 kPa), only S. scarabaei showed some activity. S. scarabaei was active from −1 to −3000 kPa in all soil types but the range of highest activity was wider in loamy sand (−1 to −1000 kPa) than in loamy sand and silt loam (−10 to −100 kPa). Persistence was determined in laboratory experiments by baiting nematode-inoculated soil with larvae of the greater wax moth, Galleria mellonella. For both Heterorhabditis spp. persistence was short at −10 kPa, improved slightly at −100 kPa, significantly at −1000 kPa, and was the highest at −3000 kPa. Both Steinernema spp. persisted very well at −10 kPa. However, S. glaseri persistence was the shortest at −10 kPa but did not differ significantly at −100 to −3000 kPa, whereas S. scarabaei persistence was not affected by soil moisture. Our observations concur with previous observations on the effect of soil moisture on entomopathogenic nematodes but also show that moisture ranges for infectivity and persistence vary among species. Differences among species may be based on differences in size and behavioral and physiological adaptations.     

Ring nematodes (Mesocriconema xenoplax) alter root colonization and function of arbuscular mycorrhizal fungi in grape roots in a low P soil

A reduction of arbuscules in roots of grapevines (Vitis vinifera) observed when ring nematodes were added to field microplots led to the hypothesis that nematode feeding suppresses arbuscules by competing for root carbohydrates. Support for this hypothesis was tested by growing ‘Pinot noir’ grapevines in a factorial experiment with three levels of initial nematode densities (0, 0.1, 1.0 nematodes g^?1 soil), two levels of light (full sun, 50% sun), and two levels of AMF (nonAMF, +AMF). Effects on plant growth were primarily driven by a light and AMF treatment interaction, such that low light increased stem dry matter accumulation at the expense of roots in +AMF vines only. Nematodes had only a minor influence on plant growth (leaf mass was reduced at the highest nematode density), but nematodes did not affect overall plant dry matter accumulation. Since nonAMF vines were severely limited by P and their growth was so poor, the impact of nematode and light treatments was further analyzed in +AMF plants only. Nematode populations, AMF colonization, and root carbohydrates were differentially affected by initial nematode density or light levels. Root biomass, and reducing sugar and starch concentrations in fine roots were reduced by low light, but the final nematode populations and arbuscule frequencies in roots were unaffected by light. Nematodes reduced arbuscules and starch concentrations in fine roots, but did not affect total colonization by AMF (hyphae, vesicles or arbuscules). Nematodes reduced plant P and K uptake at the highest density, and low light reduced Mg uptake. These findings are consistent with the hypothesis that ring nematodes suppress arbuscules in roots via competition for root carbohydrates. However, the lack of a treatment interaction between light and nematodes in our study suggests that ring nematode–AMF interactions in grape roots are controlled by more than competition for photosynthate.     

Seasonal changes in earthworm diversity and community structure in Central Côte d’Ivoire

This study assessed the impact of seasonal variation in the structure and diversity of earthworm communities of a savanna protected for 27 years in the central region of Côte d'Ivoire. Earthworm species were sampled in 1995 at monthly intervals from January to December on a 95 × 50 m experimental plot, using direct hand-sorting techniques. Each month, 10 monoliths of 1 m² × 40 cm were randomly selected from a stratified bloc design. Ten earthworm species were collected over the study period. Chuniodrilus zielae from the Eudrilidae family was by far, the most important earthworm species in term of abundance. Although earthworm diversity varied significantly, the effect of seasonal variation was unclear. Sampling efficiency of species richness varied from 80% to 100% regardless of the rainfall variation. On a seasonal time scale the C-score was lower (0.139) than expected (0.154), showing that earthworm communities exhibit a random pattern of organization. There was no evidence of non-random seasonal niche overlap because the Czechanowski index (0.50) was not significantly larger than expected (0.49).     

Reclamation of lignite mine areas with Triticum aestivum: The dynamics of soil functions and microbial communities

In this paper is studied the dynamics of the soil microbial structure and function, and enzymatic activities during a chronosequence (0, 5, 10, 15 and 20 years) after reclamation of coal mine areas with wheat (Triticum aestivum). Due to the homogeneity induced by monoculture all over the sites, similarity in the dynamics of structural and functional soil attributes was expected. Moreover, the idea of Whisenant (2002) claiming non monotonic succession unfolding during the reclamation process was checked. Soil samples were collected from the upper 12 cm of cultivated fields differing in their post-reclamation age, and they were analyzed for physicochemical variables, microbial community structure (PLFAs), catabolic profiles (Biolog Ecoplates) and enzymatic activities (β-glucosidase, urease and alkaline phosphatase). Fields outside the mine area, cultivated with the same species were used as controls. Exhibiting rapid growth from 0 to 4–5 years after reclamation, slow decline from 5 to 10 years and stabilization after 10 years, the abundances of the microbial groups (Gram⁺, Gram⁻, fungi, protozoa) showed similar dynamics. Similar dynamics displayed also the activity of alkaline phosphatase and β-glucosidase, which increased gradually from 0 to 10 years and stabilized afterwards. By contrast, the activity of urease showed an inverse temporal pattern. After 15 years, the microbial abundances, the functional diversity (Shannon index), and the soil enzymatic activities of the reclaimed soils converged to values recorded in the controls fields. Significant shifts in the microbial community structure were not detected, probably because of the type of reclamation (agricultural use). However, when the overall PLFA and carbon utilization data sets were analyzed, it was revealed that the microbial community structure changed non monotonically in the transition between 0 and 5 years after reclamation, while the carbon utilization profiles exhibited more complex successional patterns. Above findings support the idea of non monotonic successional processes in soil microbial communities.