The effect of two ant species Lasius niger and Lasius flavus on soil properties in two contrasting habitats

Ants significantly change the soil environment within the nest. The aim of this study is to contribute to ecology and thus the importance of two ant species Lasius niger and Lasius flavus in a post-mining landscape near the town of Sokolov in northwest Bohemia where both species are common. Chemical (total C, N, and available P) and microbiological parameters (respiration, cellulose decomposition and direct counts of bacteria) were investigated in both ant species in two different habitats: a tertiary clay heap after brown coal mining with a weakly developed organic layer and semi natural meadows with well developed organic horizons. Total C and N in the L. flavus mound was lower than in the surrounding soil in both stands, the same was true for total N in L. niger on the heaps. L. niger nests in both sites were significantly enriched by available P. A litter bag test with cellulose indicated lower decomposition in the ant nest in comparison with the surrounding soil. Respiration seems to be limited by lower soil moisture in the nest. However, microbial respiration, even in suitable moisture conditions, did not differ between the nest and soil (on heaps) or nest respiration was significantly lower (in L. flavus nests in the meadow). In meadow soil both species had a lower bacteria count than the surrounding soil, but the L. niger nest on the heap had higher bacterial numbers. Both species significantly alter soil conditions, although the effect on selected parameters is variable. Moreover, the result with lower nest moisture and lower decomposition rate in ant mounds indicates that soil moisture should be the next important factor limiting soil processes inside ant mounds.     

Spatial distribution of isopods in an oak–beech forest

Soil macroinvertebrates were studied in a Mediterranean-type forest on brown-pebble forest soils in southern Russia. At the site, 144 intact soil cores (76 cm² each) forming a grid of 24 × 6 units were taken in order to determine animal spatial distribution. Abundance of isopods was 166.3 ± 16.0 indiv. m^–2 and they constituted about 12% of the total macrofaunal abundance. Biomass of isopods was 3.5 g m^–2, or about 21% of the total biomass of macrofauna. Three woodlice genera (Armadillidium, Cylisticus, and Trachelipus) were found at the site. The two latter genera formed almost all (93%) of the isopod population. We found that spatial distribution of woodlice was heterogeneous: areas with 4–5 individuals per sample were neighboring those without animals. In order to study soil factors influencing isopod distribution in the brown-pebble forest soil, the size of a sample was artificially increased by combining adjacent sample units. Litter mass (r = 0.41) and loss on ignition (LOI) (r = –0.55) significantly influenced isopod distribution. Soil pH was near neutral (6.79), LOI was 8.39, and the water holding capacity was 70.9%. Pebbles comprised up to 84% of the sample's mass. Ca. 40 samples are recommended for estimation of isopod abundance in brown forest soil.     

Ecophysiology of the cave isopod Mesoniscus graniger (Frivaldszky, 1865) (Crustacea: Isopoda)

Feeding biology and thermal adaptations of the terrestrial isopod Mesoniscus graniger were studied. M. graniger is a depigmented isopod mainly inhabiting cave systems, although it has also been reported in endogeic (soil) habitats. Physiological adaptations are expected to reflect the unique environmental characteristics of caves, including restricted food sources, and stable microclimate with temperatures not exceeding about 10 °C and high relative humidity. The M. graniger from Domica and Ardovská caves (Slovakian Karst) were investigated. We identified organic deposits with associated microorganisms as sources exploited by M. graniger and assessed how these might supply essential polyunsaturated fatty acids (PUFA) in its nutrition. Algae, fungi and bat guano were found as the most important potential resources of PUFA for isopods. Digestive enzymes amylase, trehalase, saccharase and maltase were confirmed in the whole body homogenates of isopods; neither cellulolytic activity nor activities against xylan, laminaran and lichenan were observed. Amylase, maltase and cellobiase activities were also observed in bacterial strains isolated and cultured from isopod midgut, and may account for the measured whole-animal activities. In an artificial temperature gradient, M. graniger selected temperature 3.5 ± 5.4 °C with lower and upper extremes of –1.5 and 18.5 °C. Respiration, as measured by VO₂, was almost independent of temperature between 5 and 10 °C, then increased between 10 and 30 °C. These ecophysiological measures are consistent with adaptation to a stenothermal environment.     

Survival of faecal coliforms in four different types of sludge-amended soils in Botswana

This study aimed at identifying the factors that affected the survival of faecal coliforms as measured by E. coli in four types of soils in Botswana which were amended with sewage sludge. Physico-chemical and biochemical properties and coliform population in the different soils, sludge, and soil/sludge mixtures were determined after sampling, on composing the soil/sludge mixtures, and 90 days after composing. Coliform population in the different soil/sludge mixtures decreased by about 90% after 90 days. The age of the sludge used and the rate at which it was applied to the soils initially determined the population of E. coli in each soil/sludge mixture, but after 90 days, differences inherent in the different soil types were the main determinants of the E. coli population. Percentage reduction of coliforms in Type 1 sludge mixtures were lower (38%) than in Type 2 sludge mixtures (57%). Up to 79.8% of the reduction observed in E. coli population in the Barolong luvisol-sludge mixtures after 90 days was caused by reduction in pH and moisture content, while 72.6%, 84.5% and 55.1% of the reduction in E. coli population in Tuli luvisol-, arenosol- and vertisol-sludge mixtures, respectively, was accounted for by the reduction in moisture content and Olsen P concentration. Coliform survival rates varied with soil types being 12%, 6.4%, 5.3% and 5.8% for the vertisol, arenosol, Barolong luvisol and Tuli luvisol, respectively. A minimum period of 90 days should be allowed between when sludge is applied to similar soils and when seeds are sown. The exact period should, however, be determined by the properties of the soil with fine-textured soils requiring a longer period than coarse-textured soils.     

Biological effects of native and exotic plant residues on plant growth, microbial biomass and N availability under controlled conditions

The leaf litter of six tropical tree species (Acacia holosericea, Acacia tortilis, Azadirachta indica, Casuarina equisetifolia, Cordyla pinnata and Faidherbia albida) frequently used in agroforestry plantations in Sahelian and Soudano-Sahelian areas were tested for their influence on soil nitrogen content, microbial biomass and plant growth under controlled greenhouse conditions. Half of the soil was planted with onion (Allium cepa L.) seedlings and the other half was not. Two herbaceous species, Andropogon gayanus and Eragrostis tremula, were also studied. Co-inertia analysis (CIA) and one-way analysis of variance (ANOVA) analysis showed that C. pinnata and F. albida leaf powder amendment induced the highest plant growth, whereas leaf powder of E. tremula is associated to higher microbial biomass and NH₄⁺ content. Higher onion seedlings growth is associated with higher concentration of nitrogen and lignin in leaf powders. Conversely, lower plant growth is associated to higher rates of cellulose, hemicellulose and phenols in leaves. Higher rates of cellulose and hemicellulose are associated with higher microbial biomass and NH₄⁺, whereas phenols are associated to lower microbial biomass. The results showed that amendment of A. holosericea leaf powder (high concentrations of phenol) to the soil resulted in a lower microbial biomass and lower onion seedlings growth. Data showed that the plant residue quality index (PRQI) could be a useful tool to predict the effects of litter materials on root growth in glasshouse conditions. The highest values on soil and plant parameters were recorded with C. pinnata litter. While powdered leaf material increased the accessibility of substrates to microbes, more research with C. pinnata leaf litter (under a wider range of ecological conditions) is needed. It could add deeper on its agronomic impact in the tropics.     

Discrimination of Aphid Mutualists by an Ant Based on Chemical Cues

A chemical basis for discrimination between attended and unattended aphid mutualists by the ant Lasius niger (L.) (Hymenoptera, Formicidae) was investigated. In an arena bioassay, hexane extracts of the aphid Rhopalosiphum padi (L.) (Homoptera, Aphididae), which had been attended by the ant colony provoked significantly longer examination by ants than extracts of unattended aphids. Extracts of the ants themselves were significantly more active than hexane. In an olfactometer, ants spent significantly longer in the arm containing the odour of live aphids that had been attended by the ants than in arms containing the odour of unattended aphids. When unattended aphids were introduced onto an aphid-infested plant under attendance by L. niger, they suffered higher levels of attack and removal by the ants than did previously attended aphids. Unattended aphids treated with the extract of attended aphids suffered higher levels of attack than attended aphids, but lower levels of removal than unattended aphids. The results show that L. niger can discriminate between aphids that the colony have attended and unattended aphids of the same species using chemical cues.     

The influence of different vegetation patches on the spatial distribution of nests and the epigeic activity of ants (Lasius niger) on a spoil dump after brown coal mining (Czech Republic)

A study was carried out during 2001 on mine tailings in NW Bohemia aimed at describing the spatial patterns of nests distribution and epigeic activity of ants in relation to the vegetation mosaic. Lasius niger was the most abundant species of ant and its nest mounds were significantly more numerous in patches with sparse vegetation than inside dense Calamagrostis epigejos vegetation; this was particularly true for small and medium-sized nests. Small and medium nests also occurred more frequently near the edges of a given patch than in the center. Large and medium nests were randomly distributed in the area, whereas small nests had an aggregated distribution. Pitfall trapping reveal significantly higher activity of L. niger workers in tall and dense vegetation stands in comparison with low and sparse vegetation. This pattern was particularly pronounced during the peak of foraging activity in summer and was not so significant in spring or autumn. We expect that ant preferentially forage in shaded habitats during the summer months when bare soil may be too hot. The results indicated that nesting and foraging may differ in their microclimatic requirements and the formation of vegetation mosaics may be important to changes in the ant population during succession.     

Diversity of Paenibacillus durus strains isolated from soil and different plant rhizospheres evaluated by ARDRA and gyrB-RFLP analysis

Strains belonging to Paenibacillus durus isolated from the rhizosphere of various grasses and from bulk soil were previously divided into five phenotypic groups (A1–A5) based on the fermentation pattern of six carbohydrates (A1: sorbitol (+), A2: dulcitol and tagatose (+), A3: starch and glycogen (+), A4: starch, glycogen and d-arabitol (+) and A5: negative for these carbohydrates). This study aimed to assess whether plant types select for specific P. durus phenotypic groups. For that purpose, polymerase chain reaction-restriction fragment length polymorphism analysis of part of genes encoding 16S rRNA (ARDRA) and DNA gyrase subunit B (gyrB-RFLP) were used to produce genetic fingerprints. ARDRA and gyrB-RFLP data were clustered together to generate a dendrogram and two main clusters were observed. Cluster I showed a predominance of strains isolated from wheat, maize and sugarcane rhizospheres. Strains isolated from maize were distributed among the five patterns of carbohydrate metabolism, while strains isolated from sugarcane showed to be predominantly able to metabolize starch and glycogen. Neither sorbitol- nor arabitol-metabolizing strains were found in cluster II, which consisted of strains isolated from soil and from all plant species used. Our results suggest that the plants influenced the diversity of P. durus in their rhizospheres.     

Contributions of ant mounds to soil carbon and nitrogen pools in a marsh wetland of Northeastern China

Ant mounds often occur at high densities in marsh wetlands. However, little information is available regarding their impacts on soil nutrient pools in these ecosystems. We studied C_org, dissolved organic carbon (DOC), total nitrogen (TN), NO₃⁻ and NH₄⁺ concentrations in above-ground ant mounds and in soils under mounds for three ant species (Lasius flavus, Lasius niger and Formica candida), and estimated their contribution to the total soil nutrient pools in a marsh wetland. Ant impacts were greatest in above-ground soils. All measured nutrient concentrations in above-ground mounds were significantly higher than the average values in reference soils (upper 25 cm). However, except for DOC, no significant differences for nutrient concentrations existed between soils under mounds and reference soils. The impacts of ant mounds on soil C and nutrient concentrations varied by ant species. L. niger above-ground mounds stored less C_org, TN and NO₃⁻ than F. candida and L. flavus mounds, or reference soils. At the ecosystem scale, soils in above-ground mounds and under ant mounds all contained less C_org per hectare than the reference soils. Total amounts in nutrient pools from mounds of the three ant species comprised from 5.3% to 7.6% of the total in natural marsh soils. More importantly, ant mounds increased the spatial heterogeneity of nutrient pools. Thus, ant mounds can be important to a fully integrated understanding of the structure and function of wetland nutrient cycles and balances.     

Acute and chronic isopod testing using tropical Porcellionides pruinosus and three model pesticides

An approach for testing acute and chronic ecotoxicological effects of pesticides on isopods in the laboratory is presented. Laboratory cultures of tropical Porcellionides pruinosus were used. The pesticides Benomyl, Carbendazim and lambda-Cyhalothrin served as model chemicals. The toxicity tests were done with five to six concentrations and one untreated control in four replicates containing 10 individuals per vessel. The test was performed at 28 °C, in permanent darkness and it lasted 14 days. Each chemical was mixed in 250 g DW per vessel of OECD artificial, LUFA 2.2 standard, tropical artificial or tropical natural soil in acute tests. Chronic tests were performed using 150 g DW OECD artificial or LUFA 2.2 standard soil. Both adult mortality and number of juveniles showed a high sensitivity of P. pruinosus towards lambda-Cyhalothrin while Carbendazim and Benomyl had a very low and no toxicity, respectively. Further research and optimization of the chronic test design are required.     

Assessing spatial variability of soil enzyme activities in pasture topsoils using geostatistics

The purpose of this study was to assess the spatial variability of the activity of three hydrolytic enzymes, i.e. urease activity (UAc), alkaline phosphatase activity (APAc), and arylsulfatase activity (ASAc), in pasture topsoils using geostatistics. Enzyme activities along a transect in a 1.35-ha pasture were determined using 77 soil samples from the upper 20 cm of soil. UAc varied from 101.0 to 182.7 μg N g⁻¹ soil h⁻¹; APAc varied from 1.56 to 3.62 μg p-nitrophenol g⁻¹ soil h⁻¹; and ASAc varied from 1.50 to 3.26 μg p-nitrophenol g⁻¹ soil h⁻¹. The linear models fit the best semivariogram models for UAc, APAc, and ASAc. Semivariograms for enzyme activities exhibited spatial dependence with ranges of influence of approximately 124.7 m.     

Species specific effects of ants on microbial activity and N-availability in the soil of an old-field

Microbial biomass and activity as well as N-availability were measured in the mounds of three ant species strongly differing in foraging strategy and mound architecture: Myrmica scabrinodis, Lasius niger and L. flavus. Soil microbial biomass (C_mic) was significantly increased in the mounds of all three ant species. This positive effect was due to the accumulation of organic matter (C_org) within the mounds. Microbial activity was increased in M. scabrinodis mounds only. Available N_min was accumulated in all mound types, independent of the feeding mode of the ants, with Lasius mounds having significantly higher N_min content than M. scabrinodis mounds. It is hypothesised that the differences between the mound types are due to differences in nest architecture, especially the integration of grassy vegetation. Higher microbial activity in M. scabrinodis mounds may be a consequence of supplementary energy provided by root exudates. The amount of N_min in M. scabrinodis mounds may be reduced by increased plant uptake and by immobilisation within the microbial biomass.     

Altitudinal terrestrial isopod diversity

We have assessed the diversity of terrestrial isopods across an elevational and habitat gradient on Mt. Panachaiko (NW Peloponnisos, Greece). Previous knowledge on the biodiversity of this mountain was restricted to very few records of individual species, and no systematic sampling had ever been applied for any animal taxon. We selected the most representative habitat types within an altitudinal range from 750 to 1700 m a.s.l., where we applied qualitative and quantitative monthly sampling using hand collecting and pitfall traps for 6 months during the snow-free period (June–November). We sampled three sites with maquis vegetation, one site with fir forest, one with sparse hawthorn vegetation and two at a highland meadow, and we compared the distribution and abundance patterns of isopod species among these habitat types. Overall, 13 isopod species were found, seven of which were also captured in pitfall traps. One species, Armadillidium lobocurvum, was extremely abundant at the most elevated sites, resulting in very uneven patterns of abundance. The habitat types with higher diversity of isopod species were the sparse hawthorns and the open maquis, and the richest month was July. We also discuss the phenology of the most abundant species at the highland meadows.     

Ecology of the earthworm Allolobophora carpathica in field and laboratory studies

Allolobophora carpathica is an earthworm species found in the Eastern Carpathian mountain region, but little information is available on its ecology. Field sampling in beech woodland of the Bieszczady National Park, SE Poland, found this species in soils with a pH of less than 5.0 and C:N ratios of 12 to 13. From sampling over 2 years, at 4 sites with differing sub-vegetation, a mean density of A. carpathica of 6.75 individuals m^-2 with a biomass of 8.65 g.m^-2 was recorded. The largest mature adults were in excess of 14.0 g but there were significant differences (p < 0.01) between sampling sites. Seasonal patterns of abundance were observed.To obtain more data on the growth and breeding biology of this species, specimens were collected from the field, taken to laboratories and maintained in mesocosms under controlled environmental conditions. Cocoon production was 0.88 cocoons per earthworm per month at 15^oC, but under fluctuating temperature conditions (16 - 24^oC) no cocoon production occurred. The mean cocoon biomass was 83 mg  (n = 104) and incubation took 178 days at 15^oC (n = 14), although hatchability was low (22%) under these conditions. Growth from the hatchling stage, (mean mass 86 mg; n = 18), to maturity (c. 8.5 g) took 8 - 12 months at 12^oC.     

Abundance of the earthworm Lumbricus terrestris in relation to subsurface drainage pattern on a sandy clay field

Subsurface drainage induces systematic spatial variability in soil properties which may be reflected in the abundance and distribution of soil organisms. We compared the population density of the deep burrowing earthworm Lumbricus terrestris L. above and between tile subdrains in 41 sample pairs on an eight hectare grass field. Above the drains the median number of  individuals was twice as high and their total fresh mass five times as high as between the drains (4.5 vs. 2.1 individuals m^-2  and 9.6 vs. 1.9 g m^-2, respectively). The mean difference (above drain – between drains) was 2.5 individuals m^-2  (95% CI = 1.0 to 4.0) and 6.6 grams m^-2 (95% CI = 3.6 to 9.6). The relatively larger difference in fresh mass was due to a high proportion of adult individuals above drains. One likely explanation for the pattern of abundance is that the lowered water table level near the drains provides an environment beneficial for the population growth of L. terrestris. Due to the role of L. terrestris burrows as flow paths of percolating water the observations may have implications on subdrain function.     

Soil engineering ants increase CO2 and N2O emissions by affecting mound soil physicochemical characteristics from a marsh soil: A laboratory study

As ecosystem engineers, ants can mediate soil processes and functions by producing biogenic structures. In their mounds, ants not only directly produce CO₂ by respiration, but may also indirectly impact soil greenhouse gas emissions by affecting substrate availability and soil physicochemical characteristics. Recent studies focused on overall gas production from ant mounds. However, little is known about mound material respiration and N₂O emissions in ant mounds in wetlands. We measured CO₂ and N₂O emissions from mound soils of three different ant species (Lasius niger Linnaeus, Lasius flavus Fabricius, and Formica candida Smith) and natural marsh soils in a laboratory incubation experiment. On the whole, average soil CO₂ and N₂O emission rates from ant mounds were significantly higher than from the natural marsh soils. Over the 64 days incubation, the cumulative soil CO₂ and N₂O production from ant mounds was, respectively, 1.5–3.0 and 1.9–50.2 times higher than from the natural soils. Soil gas emissions from ant mounds were significantly influenced by the specific ant species, with soil CO₂ and N₂O emissions from L. niger mounds being higher than those from F. candida or L. flavus mound soils. Cumulative CO₂ and N₂O emissions from ant mound soils were positively correlated with soil clay, total carbon, dissolved organic carbon, total nitrogen and NH₄⁺ content. Our laboratory results indicated that mound soil is an important source of CO₂ and N₂O emission from ant mounds in marshes, making mounds potential “hot spots” for CO₂ and N₂O emissions. Ants may increase the spatial heterogeneity of soil gas emissions by changing mound soil physicochemical properties, especially carbon and nutrition content, and soil texture. Contributions from ant mound materials should be considered when describing soil C and N cycles and their driving factors in wetland ecosystems.     

Ant-induced soil modification and its effect on plant below-ground biomass

Lasius flavus is a dominant mound-building ant species of temperate grasslands that significantly modifies soil parameters. These modifications are usually the result of workers’ activities such as food accumulation and nest construction. An alternative hypothesis that could explain changes in soil is colony founding in areas of higher soil fertility.In our study we investigated several soil parameters sampled in 10 ant nests and adjacent (control) plots in mountain grassland in Slovakia. The alternative hypothesis was tested by comparing occupied and abandoned mounds. While we found increased concentrations of available P and K in the nests, concentrations of total C, total N, Ca²⁺ and Mg²⁺ were lower there. We propose that differences found between the soil of nests and control plots are entirely a product of ant activity during mound occupancy and not due to initial soil differences during nest establishment. This was confirmed by the comparison of occupied and abandoned nests in which the soil fertility of abandoned nests was similar to conditions in the surrounding soil.Along with the modification of soil chemistry, we recorded changes in soil physical properties and the vertical distribution of nutrients. Ant nests were characterized by the dominance of 0.02–0.1 mm particles and lower bulk density. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased and bulk density increased with depth. Root biomass followed the vertical pattern observed with nutrients: in control plots, most roots were concentrated in the uppermost layer (0–3 cm), whereas they were evenly distributed along the vertical gradient in the nests. We also found that rhizome internodes of Agrostis capillaris were thinner and longer in plants from the mounds. Changes in soil physical properties, vertical distribution of nutrients and root biomass in the nests are most probably a consequence of mounding and soil mixing (bioturbation), which has been less reported on in ant-soil studies.     

Preliminary observations on the natural variation in the endogenous rhythm of the desert Isopod Hemilepistus reaumurii

The desert woodlouse Hemilepistus reaumurii lives in monogamous pairs, together with their offspring, in self-dug burrows. Every burrow contains only one family. This animal is active on the surface from the beginning of spring to autumn. It remains in the burrow during the hottest part of the day, to avoid the heat, but is active at the surface during morning and evening. During the winter, low temperature prevents its above ground activity. Freshly collected animals, from the north of Kairouan (Tunisia) were transferred to a controlled environment cabinet in the laboratory and their locomotor activity monitored as individuals or in male/female pairs, in annular chambers equipped with an infrared activity recording system. For the first 7 days of recording, the animals were kept in a light–dark cycle in phase with the natural diel cycle. For the second 7 days, animals were maintained in constant darkness. The temperature was held constant at 18±1 °C. Analysis of preliminary data indicates that both individuals and pairs exhibit an endogenous rhythm of locomotor activity with a circadian periodicity. Activity was mostly confined to the hours of the photophase (1–7 days) or to those of subjective day (8–14 days). The activity pattern showed two main peaks, around dusk and dawn, respectively. This bimodal circadian rhythm persisted for as long as the experiments were run, and was clearer in individual recording than in pair recording. The characteristics and biological significance of the rhythm are discussed.     

Intermediate tidal stress promotes the detritivore-mediated decomposition of Spartina litter

Saltmarshes, functionally important habitats in the marine–terrestrial ecotone that are regularly affected by tidal inundation, are mainly detritus-based in terms of fluxes of nutrients and energy. With respect to the mediating influence of saltmarsh detritivores on microbial colonisation of detritus and on decomposition processes, we tested whether the “intermediate disturbance hypothesis” (IDH) is also applicable to the effects of stress in this stressful environment. Decomposition experiments with litter of the cordgrass, Spartina anglica, and with terrestrial [Porcellio scaber (Isopoda)] and marine/semi-terrestrial [Orchestia gammarellus (Amphipoda)] detritivores as well as animal-free controls were carried out in an artificial saltmarsh system. Different daily flooding regimes served as experimental levels of stress. Both litter mass loss and microbial respiration were mostly higher under aquatic than under terrestrial conditions, no matter whether detritivores were present or not. Considering the intertidal zone, low to intermediate daily inundation rates resulted in increased microbial respiration and an increased influence of detritivores on litter mass loss in early stages of cordgrass decomposition with high rates of detritus mass loss, and intermediate tidal stress led to higher microbial cell counts throughout the entire experiment. Summarised over 3 months, regression analyses suggested that microbial activity and detritus mass loss show a trend towards highest values at low inundation rates and under permanent inundation, although microbial density was higher under longer daily inundation. Access to detritus by detritivores enhanced both litter mass loss and microbial respiration, especially in later decomposition stages, whereas microbial density was reduced by detritivores. In conclusion, we predict that overall the decomposition of cordgrass detritus in saltmarshes is promoted in the intermediate to high area of the intertidal zone with daily inundation of ca. 4–10 hours where both marine and terrestrial detritivores have access to promote decomposition processes through feeding and mediating microbial activity.