Phenylpyrazoles impact on Folsomia candida (Collembola)

Effects of the broad-spectrum insecticide fipronil were investigated on a non-target insect living in the soil, the springtail Folsomia candida Willem. Fipronil induced a significant reduction in juvenile production (PNEC = 250 μg kg⁻¹ dry soil), which seemed to be linked with an impact on the first stages of springtail development: juveniles and 7-day-old adults. These young organisms have a thinner integument, a smaller mass body and a weaker detoxification efficiency and were more sensitive than adults (14 days old) to fipronil and phenylpyrazole derivatives. Contact toxicity for juveniles was measured (LC₅₀(96 h)) giving the following values: fipronil, 450 μg l⁻¹; sulfone-fipronil, 430 μg l⁻¹; sulfide-fipronil, 160 μg l⁻¹. F. candida organisms were able to avoid contaminated food because phenylpyrazoles decreased food appetency. However, F. candida could bioaccumulate fipronil through trans-tegumental penetration (BAF_96 h = 160) and its high biotransformation rate inside springtail bodies (1 ng fipronil metabolized day⁻¹ individual⁻¹) was suspected to increase this process. Under natural conditions, phenylpyrazoles risk assessment on springtails seems to be weak due to their capacity of avoiding high contaminated zones and their biochemical tolerance to this class of insecticides.     

Genetic variation in a subterranean arthropod (Folsomia candida) as a method to identify low-permeability barriers in an aquifer

Folsomia candida (order Collembola), a common soil arthropod, has recently been described living in a shallow (2.5–5.7 m below surface), unconsolidated aquifer in southwestern Michigan. F. candida was haplotyped from 14 wells using inter-simple sequence repeats (ISSRs) markers, and genetic variation in F. candida was used as a bioindicator to identify pore scale to mesoscale migration barriers in the aquifer. With one exception, individual haplotypes were only found in single wells. A significant relationship was identified between interpopulation genetic differentiation and geographic distance, and F. candida exhibits genetic population structuring over a very fine geographic scale (0.65 km²). Monmonier's algorithm was used to identify two most likely subsurface barriers to migration. Hypothesized barriers divided the F. candida populations into three genetically distinct groups, with two groups separated by only 15 m. These groupings are not dependent on groundwater flow direction, and are supported by a minimum spanning network and AMOVA analysis. Because F. candida movement is limited by pore size, these barriers identify local areas of low permeability in the aquifer material. The study suggests that F. candida may serve an important role in identifying geological characteristics and patterns in aquifers that may be difficult to evaluate by other means.     

Effects of Folsomia candida (Collembola) on the microbial biomass in a grassland soil

Summary The effects of the presence of Folsomia candida on substrate-induced respiration, CO₂-C evolution, bacterial count and NH ₄ ⁺ -N were investigated in a grassland soil. Differences in these parameters, with the exception of NH ₄ ⁺ , were correlated with the age of the collembolan Folsomia candida. In the presence of juvenile animals total CO₂-C evolution was enhanced, but substrate-induced respiration and the bacterial count were unchanged. In fumigated soil with imagos, substrate-induced respiration and the number of bacteria were increased, but total CO₂-C evolution was unaltered. Different food selection strategies between adults and juvenile animals may explain the results.     

Toxicity of lead pollution to the collembolan Folsomia candida in Ferri-Udic Cambosols

Toxic effect of lead(Pb) pollution on Collembola in soils has seldom been studied in depth, which is especially true for growth responses since the juveniles are very small and numerous. A single species test was conducted using the collembolan Folsomia candida as the indicator species, and soil Pb pollution(at Pb concentrations of 0, 300, 600, 1 200, 2 400, and 4 800 mg kg~(-1)) was simulated by mixing Pb(NO_3)_2 with a natural unpolluted soil. Adult survival, reproduction, body length, and body Pb concentration were determined. Adult survival and reproduction started to decrease at soil Pb concentrations of 1 200 and 600 mg kg~(-1), respectively. Lead concentrations in adult and juvenile bodies increased with increasing Pb concentration in soil. The percentage and individual abundances based on body length analysis showed that the larger adults(2.1–2.6 mm, P 0.01) were more sensitive to soil Pb concentration than the intermediate(1.9–2.1 mm, P 0.001) and smaller(1.7–1.9 mm, P 0.001) adults. Similarly, the larger juveniles(1.0–1.4 mm, P 0.001) were more sensitive to soil Pb concentration than the intermediate(0.6–1.0 mm, P 0.001) and smaller(0.3–0.6 mm, P 0.001) juveniles. For both adults or juveniles, the abundance and percentage of larger individuals declined significantly with increasing soil Pb concentration, suggesting that larger individuals were more sensitive to soil Pb pollution. Therefore, body length features, especially the percentage and abundance of larger individuals, would be potential bio-indicators of soil Pb pollution and possibly other types of soil pollution.     

Site condition, fertility gradients and soil biological activity in a New Zealand frost-flat heathland

Gradients in stressed areas potentially provide a powerful tool to interpret relations between soil biodiversity and site quality. We measured soil chemistry, soil microbiology and nematodes along three transects representing a fertility gradient and at a disturbed site near a road in a Dracophyllum subulatum-dominated shrubland in which frosts are a major factor in preventing succession to forest; we used D. subulatum size as a site-quality index. Significant correlations between both shrub height and shrub growth rate and volumetric measures of total soil phosphorus and anaerobically mineralisable nitrogen indicate that nitrogen and phosphorus regulate plant growth. Microbial biomass and total nematode abundance significantly increased with greater plant growth, presumably in response to greater litter input. Conversely, neither heterotrophic microbial diversity nor nematode diversity was correlated with shrub performance along the transects. Litter was from a single species and thus likely similar in quality so changes in microbial or nematode diversity might not be expected. In this oligotrophic environment, nutrient levels were not only the important regulators of plant growth but also appeared to have an indirect influence on the size of the microbial and nematode populations.     

Feeding preferences of the collembolan Onychiurus sinensis for fungi colonizing holm oak litter (Quercus rotundifolia Lam.)

Ten fungi isolated from decaying holm oak leaves (Quercus rotundifolia Lam.) have been presented to the collembolan species Onychiurus sinensis (Hexapoda). The attractiveness and selectivity of the ten fungi was investigated taken into account the effect of the substrate on which the fungus was growing (malt-agar or litter) and the effect of fungal odour. Furthermore, moulting, growth, survival and reproduction of O. sinensis in the presence of each of the ten test fungi were studied. Mucor plumbeus and Trichothecium roseum were the most preferred whatever the culture substrate and their odour was the most attractive. Two fungi (Penicillium spinulosum and the Basidiomycete S41) attracted Collembola by their odour but were not preferred as food sources. The animals could survive and reproduce on a mono-diet of several of our test fungi, but not on the Basidiomycete S41 and on Trichoderma polysporum.     

Exploitation of litter and soil by the train millipede Parafontaria laminata (Diplopoda: Xystodesmidae) in larch plantation forests in Japan

Swarms of the train millipede (Parafontaria laminata) are known to occur every 8 years; during the swarms, adults emerging from the soil have an extremely high density in natural and plantation forests in central Japan. Their influence on organic layer accumulation on forest floors was investigated under field conditions in plantation larch forests in central Japan, before and after the adult swarming period of 2000. In addition, the adult millipede feeding preference and the amount of food consumed were observed in the laboratory. The field density of adults ranged from 11 to 311 individuals m⁻² in October 2000; the highest biomass was 28.6±16.4 g dry wt m⁻². Reduction of the forest floor organic layer was density- dependent when the population consisted of 7th instar larvae; however, the adult population did not consume in a density-dependent manner. Higher levels of geophagy were observed in high-density treatments in the laboratory. We hypothesized that the geophagy of the millipedes was partly supported by the naturally high organic matter content of Andosol, and that soil consumption would sustain an extremely high biomass in a temperate conifer forest soil.     

Microbial biomass and activity in soil and litter underPinus sylvestris, Picea abies andBetula pendula at originally similar field afforestation sites

Microbial biomass C and N, and activities related to C and N cycles, were compared in needle and leaf litter, and in the uppermost 10 cm of soil under the litter layer in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and silver birch (Betula pendula L.) stands, planted on originally similar field afforestation sites 23–24 years ago. The ground vegetation was differentiated under different tree species, consisting of grasses and herbs under birch and pine, and mosses or no vegetation with a thick layer of needles under spruce. The C:N ratio of the soils was 13–21 and the soil pH_{CaCl 2} 3.8–5.2. Both showed little variation under different tree species. Microbial biomass C and N, C mineralization, net ammonification, reduction) did not differ significantly in soil under different tree species either. Birch leaf litter had a higher pH_{CaCl 2} (5.9) than spruce and pine needle litter (pH 5.0 and 4.8, respectively). The C:N ratio of spruce needles was 30, and was considerably higher in pine needles (69) and birch leaves (54). Birch leaves tended to have the highest microbial biomass C and C mineralization. Spruce needles appeared to have the highest microbial biomass N and net formation of mineral N, whereas formation of mineral N in pine needles and birch leaves was negligible. Microbial biomass C and N were of the same order of magnitude in the soil and litter samples but C mineralization was tenfold higher in the litter samples.     

Genetic differentiation of the parthenogenetic soil collembolan Isotoma notabilis along a copper gradient based on random amplified polymorphic DNA

Five species of collembolans were collected at 24 sampling areas in a copper polluted field. The most abundant species was Isotoma notabilis found at half the sampling sites, in total 490 individuals. Two hundred and fifty-two specimens of these, representing seven sampling areas were analysed by means of random amplified polymorphic DNA using three decamer primers. Two primers each revealed eight phenotypes and the third showed six phenotypes. Distribution of the phenotypes was not homogenous within the sampling area. This result could not be explained as an outcome of either the copper content in the soil or the grass biomass, but was more likely an effect of colonisation from the areas surrounding the field.     

Growth of Lumbricus terrestris and Aporrectodea caliginosa in an acid forest soil, and their effects on enchytraeid populations and soil properties

A laboratory experiment was carried out to test the hypothesis that the earthworms Lumbricus terrestris and Aporrectodea caliginosa are able to maintain their populations and reproduce in the acid forest soil of a deciduous forest where no lumbricids were found in the field. The experiment was conducted in 45-l containers in which layers of mineral subsoil, humus and organic topsoil collected from the site were established. Both species survived and at least L. terrestris reproduced during the 60 weeks’ incubation. Burrows and middens of L. terrestris were recorded and quantities of litter were consumed. The presence of lumbricids increased the organic matter content of humus, reduced the acidity of the topsoil and humus layers, and suppressed the population of the enchytraeid Cognettia sphagnetorum. A dense population of Enchytraeus albidus was found in L. terrestris middens. It is concluded that edaphic factors do not explain the absence of earthworms, but isolation from cultural landscapes and lack of opportunity to colonize the site from the surroundings is the decisive factor.     

Immobilization and mineralization of nitrogen in a saline and alkaline soil during microbial use of sugarcane filter cake amended with glucose

A 42-day incubation was conducted to study the effect of glucose and ammonium addition adjusted to a C/N ratio of 12.5 on sugarcane filter cake decomposition and on the release of inorganic N from microbial residues formed initially. The CO₂ evolved increased in comparison with the non-amended control from 35% of the added C with pure +5 mg g⁻¹ soil filter cake amendment to 41% with +5 mg g⁻¹ soil filter cake +2.5 mg g⁻¹ soil glucose amendment to 48% with 5 mg g⁻¹ soil filter cake +5 mg g⁻¹ soil glucose amendment. The different amendments increased microbial biomass C and microbial biomass N within 6 h and such an increase persisted. The fungal cell-membrane component ergosterol initially showed a disproportionate increase in relation to microbial biomass C, which completely disappeared by the end of the incubation. The cellulase activity showed a 5-fold increase after filter cake addition, which was not further increased by the additional glucose amendment. The cellulase activity showed an exponential decline to values around 4% of the initial value in all treatments. The amount of inorganic N immobilized from day 0 to day 14 increased with increasing amount of C added, in contrast to the control treatment. After day 14, the immobilized N was re-mineralized at rates between 1.3 and 1.5 μg N g⁻¹ soil d⁻¹ in the treatments being more than twice as high as in the control treatment. This means that the re-mineralization rate is independent of the actual size of the microbial residues pool and also independent of the size of the soil microbial biomass.     

Continuous defoliation of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) and associated changes in the composition and activity of the microbial population of an upland grassland soil

A microcosm study was conducted to investigate the effect of continuons plant defoliation on the composition and activity of microbial populations in the rhizosphere of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Continuons defoliation of ryegrass and clover resulted in sigmficant (P <0.01) increases in soil microbial biomass, although whilst increases were measured from day 2 in soil sown with clover significant increases were only seen from day 21 in soil sown with ryegrass. These increases were paralleled, from day 10 onwards, by increases in the numbers of culturable bacteria. Numbers ofPsendomonas spp. also increased in the later stages of the study. No influence on culturable fungal populations was detected. Whilst shifts in the composition of the microbial populations were measured in response to defoliation there was little effect on microbial activity. No changes in either dehydrogenase activity or microbial respiration in the rhizosphere of ryegrass or clover were measured in response to defoliation, but both dehydrogenase activity and microbial respiration were greater in ryegrass than clover when values over the whole study were combined. Continuous defoliation resulted in significant (P <0.001) reductions in the root dry weight of ryegrass and clover, of the order 19% and 16%, respectively.     

无机氮和葡萄糖添加对土壤微生物生物量和活性的影响

以黄淮海平原潮土为研究对象,通过室内恒温恒湿培养方法,比较研究了土壤中纤维素是否存在时,外源无机氮和葡萄糖添加对土壤微生物生物量及其活性的影响变化。实验设8个处理,包括不加任何物质的对照(CK)、添加无机氮(N)、葡萄糖(G)、纤维素(C)处理及葡萄糖和无机氮同时添加(G+N)处理,以及在纤维素存在基础上添加无机氮(C+N)、葡萄糖(C+G)、葡萄糖和无机氮同时添加(C+G+N)处理。在33天培养时间内,分别在不同的时间间隔内测定了土壤CO2累积释放量、微生物生物量碳(Cmic)、及脱氢酶(DHD)、β-葡萄糖苷酶(GLU)、过氧化氢酶(CAT)、碱性磷酸酶(APH)活性。结果表明,所有测定的微生物性质在CK与C处理间均没有显著性差异。与CK和C处理相比,其他所有处理的土壤CO2累积释放量均显著增加,其中C+G+N处理达最大值;G、G+N、C+G、C+G+N处理的土壤Cmic含量及DHD和APH活性显著提升,尤其在培养的前14天,而N和C+N处理则与CK处理相似,表示添加葡萄糖可显著增加上述处理生物活性水平,而添加无机氮则不能。添加无机氮和葡萄糖对GLU和CAT的影响不明显,大部分情况下它们在处理间没有表现出显著性差异。相关性分析表明,CO2释放速率始终与APH活性成显著正相关,但与Cmic和其他酶活性之间的相关关系则随着培养时间的不同而发生变化,这可能与不同培养时间的微生物组成或微生物利用底物的模式发生改变有关。聚类分析结果进一步表明,8个处理的土壤微生物活性水平可明显分成3组,其中活性水平最高的组只包含C+G+N处理,该结果提示在难分解纤维素存在时,无机氮和易利用有机碳的同时添加对提升土壤微生物活性的重要性。     

紫茎泽兰和黄顶菊入侵对土壤微生物群落结构和旱稻生长的影响

为比较入侵植物与本地植物对土壤微生态影响的差异, 探索外来植物入侵的土壤微生物学机制, 本研究通过同质园试验, 比较分析了2种入侵菊科植物(紫茎泽兰、黄顶菊)和2种本地植物(马唐、猪毛菜)对土壤肥力和微生物群落的影响, 并通过盆栽反馈试验验证入侵植物改变后的土壤微生物对本地植物旱稻生长的反馈作用。同质园试验结果表明: 2种入侵植物和2种本地植物分别对土壤微生态产生了不同的影响, 尤其是紫茎泽兰显著提高了土壤有效氮、有效磷和有效钾含量,紫茎泽兰根际土壤中有效氮含量为39.80 mg·kg^-1,有效磷含量为48.52 mg·kg^-1。磷脂脂肪酸指纹图谱结果表明, 2种入侵植物与2种本地植物相比, 较显著增加了土壤中放线菌数量, 而紫茎泽兰比其他3种植物显著增加了细菌和真菌数量。盆栽结果表明: 黄顶菊生长过的土壤灭菌后比灭菌前旱稻株高增加113%, 紫茎泽兰也使旱稻的株高增加17%。由以上结果可知, 紫茎泽兰和黄顶菊可能通过改变入侵地土壤的微环境, 形成利于其自身生长扩散的微生态环境从而实现其成功入侵。     

Attraction to prey and prey-associated odours by the predatory mite Hypoaspis aculeifer in a soil experimental system

In terms of food searching and trophic interactions among soil organisms volatile signalling plays a crucial role. Still, volatile-based foraging decisions are poorly understood, especially as the dispersal and perception of cues is more restricted within the soil pore space than in simple laboratory approaches where volatiles disperse freely in the air. Focusing on the tritrophic interaction between the soil fungus Trichoderma viride, the fungivorous collembolan Folsomia candida and the predatory mite Hypoaspis aculeifer, we tested the effect of prey and prey-associated volatile signals on the food choice decision of the predatory mite in a laboratory experiment under soil conditions as well as the possible occurrence and relevance of grazing-induced indirect defence signals. The mites showed a clear preference for ungrazed and grazed fungal mycelium. However, we found no evidence of induced indirect defence as ungrazed mycelium was preferred to grazed fungus.     

Growth rates of Aporrectodea caliginosa (Oligochaetae: Lumbricidae) as influenced by soil temperature and moisture in disturbed and undisturbed soil columns

Earthworm growth is affected by fluctuations in soil temperature and moisture and hence, may be used as an indicator of earthworm activity under field conditions. There is no standard methodology for measuring earthworm growth and results obtained in the laboratory with a variety of food sources, soil quantities and container shapes cannot easily be compared or used to estimate earthworm growth in the field. The objective of this experiment was to determine growth rates of the endogeic earthworm Aporrectodea caliginosa (Savigny) over a range of temperatures (5–20 °C) and soil water potentials (−5 to−54 kPa) in disturbed and undisturbed soil columns in the laboratory. We used PVC cores (6 cm diameter, 15 cm height) containing undisturbed and disturbed soil, and 1 l cylindrical pots (11 cm diameter, 14 cm height) with disturbed soil. All containers contained about 500 g of moist soil. The growth rates of juvenile A. caliginosa were determined after 14–28 days. The instantaneous growth rate (IGR) was affected significantly by soil moisture, temperature, and the temperature×moisture interaction, ranging from −0.092 to 0.037 d⁻¹. Optimum growth conditions for A. caliginosa were at 20 °C and −5 kPa water potential, and they lost weight when the soil water potential was −54 kPa for all temperatures and also when the temperature was 5 °C for all water potentials. Growth rates were significantly greater in pots than in cores, but the growth rates of earthworms in cores with undisturbed or disturbed soil did not differ significantly. The feeding and burrowing habits of earthworms should be considered when choosing the container for growth experiments in order to improve our ability to extrapolate earthworm growth rates from the laboratory to the field.