Effects of Cd and Pb on the survival and juvenile production of Sinella coeca and Folsomia candida

Degradation factors can cause both quantitative and qualitative changes in fauna and thus affect soil functioning. The use of bio-indicators may help to detect environmental changes. The aim of this study was to evaluate the effects of lead and cadmium on the biology (mortality, reproduction, egg hatching) of two euedaphic collembolans, Sinella coeca and Folsomia candida and to evaluate sensitivity differences between the two species. The results showed that low concentrations of lead did not cause dramatic effects on the survival and reproduction of both species. Reproduction of both species was reduced when the soil contained a nominal concentration of Pb at 1000 μg g^–1. S. coeca and F. candida showed a high sensitivity to cadmium and both their reproduction and survival were significantly reduced on exposure to 50 μg g^–1. Moreover, egg hatching of F. candida was affected by the cadmium concentrations in the soil, and by the amount of time that the eggs stayed in contact with cadmium. This study showed that the inhibition determined by Cd on F. candida juvenile production was caused in part by inhibition of deposition and, in part, by reduction of egg viability.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g⁻¹ medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g⁻¹. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g⁻¹) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g⁻¹) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Alternative procedure for total phosphorus determination in plant tissue

Abstract

Surface liming will prevent the formation of an ‘acid roof’ on the surface of soil cropped in no‐till corn (Zea mays L.). A study was begun in 1985 to determine the effectiveness of unincorporated liming in raising pH in no‐till soil which had developed significant acidity throughout the upper 15 cm. Lime was applied at 0, 3.36, 6.72 and 10.08 Mg ha^‐1. All lime was applied on 26 April 1985 and was not incorporated. The pre‐liming pH at 0‐5 cm below the surface was 4.5; after two months the pH was raised to 5.6, 5.8, and 6.0 by 3.36, 6.72 and 10.08 Mg ha^‐1 of lime, respectively. After 19 months soil‐pH was raised to 6.0, 6.4 and 6.6 by liming at 3.36, 6.72 and 10.08 Mg ha^‐1 respectively. Soil‐pH below 5 cm was not affected by any rate of lime during the first 19 months after liming. Tissue analysis of corn ear leaves indicated that calcium uptake was increased significantly by lime in 1985, while manganese uptake was significantly reduced. In 1986, increases in calcium were greater than in 1985 and addtional significant reduction in manganese uptake was accompanied by significantly reduced zinc and copper uptake. In both 1985 and 1986, a trend toward lower average corn grain yield in unlimed plots than in limed plots was noted, but the yield increases due to lime were not statistically significant in either year. This study will be continued as a long term investigation of lime penetration into no‐till soil and response of corn to soil‐pH changes.     

Food choice and reproductive success of Folsomia candida feeding on copper-contaminated mycelium of the soil fungus Alternaria alternata

We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g^?1 medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g^?1. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g^?1) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g^?1) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations.     

Effect of Anions in Simulated Precipitation on the Uptake of Heavy Metals and Aluminum by Brassica Rapa L. Grown in Heavy -Metal -Contaminated Sandy Soil

This study investigated the effect of anions on the uptake of heavy metals and aluminum by Brassica rapa L. from non-contaminated, Cd-contaminated, and sewage sludge compost (SSC)-amended sandy soil. Four types of artificial precipitation were applied: deionized water (pH 5.7) as a control, and solutions of HNO₃, H₂SO₄, and HCl prepared to pH 4.5. Precipitation was applied daily during the last 20 d of cultivation. The pH of the Cd-treated soil after harvest was not affected by any precipitation treatment. Shoot concentrations of heavy metals and Al were unaffected by any treatments on non-contaminated soil. In contrast, all acid treatments increased the Cd concentration in shoots grown on Cd-contaminated soil, but only HNO₃ precipitation increased it in SSC-amended soil. These results indicate, even without large soil pH change, there is a possibility that the Cd uptake by B. rapa L. depends on anions in precipitation and chemical form of Cd in the soil under conditions of heavy metal enrichment.     

Effects of copper rates and soil ph on growth and nutrient uptake by citrus seedlings

Abstract

Soil properties, primarily pH and organic matter, influence phytotoxicity of copper (Cu). A pot experiment was conducted to evaluate the effects of copper additions (0, 25, 50, 100, 200, and 400 mg kg^?1) to three different soils [Myakka fine sand (pH 5.7), Candler fine sand (pH 6.5), and Oldsmar fine sand (pH 8.2)] on growth, and uptake of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and copper (Cu) by Swingle Citrumelo (SC) seedlings. In unamended soils, the seedling growth was similar in the Myakka and Candler fine sands (pH 5.7 to 6.5), but was significantly greater in the Oldsmar fine sand (pH 8.2). Increasing the rate of Cu from 0 to 400 mg kg^?1 decreased the soil pH by 0.98 unit in the Candler fine sand, by 1.57 pH unit in the Myakka fine sand, and negligible effects on the pH of the Oldsmar fine sand. The growth of SC seedlings decreased significantly with an increase in Cu rates in the Myakka and Candler fine sands, but not in the Oldsmar fine sand. The Cu concentration in the leaves and roots increased substantially with an increase in the Cu rate applied to the Candler and Myakka fine sands while the effect was marginal in the Oldsmar fine sand. The above effect was more pronounced on the Cu concentration in the roots than in the leaves. Increased rate of Cu application decreased the uptake of P, Mg, Ca, and K in the roots and leaves of the seedlings grown in the Myakka and Candler fine sands but not in the Oldsmar fine sand.     

Phosphorus Speciation and Nutrient Stoichiometry in the Soil-Plant System During Primary Ecological Restoration of Copper Mine Tailings

The effects of plant vegetation on phosphorus(P) speciation, pH, total carbon concentration, total nitrogen concentration, and alkaline phosphatase activities were investigated to explore the P uptake strategy of plants in low-P soil and to determine the nutrient stoichiometric ratio changes in the rhizosphere of plants(Imperata cylindrica, Miscanthus floridulus, Zoysia sinica, Artemisia lavandulaefolia, Indigofera pseudotinctoria, and Conyza canadensis) which had grown for approximately 15 years in copper mine tailings, East China. The results showed that the average pH values in the rhizosphere decreased by 0.06–1.37 compared with those in the non-rhizosphere. The alkaline phosphatase activities of the rhizosphere were significantly higher than those in the non-rhizosphere.The mean concentrations of aluminum(Al)-and iron(Fe)-bound P and Ca_2-P(CaHPO_4) in the rhizosphere of all plants were 5.4% to 87.7%, 49.2% to 214.2%, and 86.6% to 147.6% higher than those in the non-rhizosphere, respectively. Except for Ca_8-P(Ca_8H_2(PO_4)_6)and Ca_(10)-P(Ca_(10)(PO_4)_6(OH)_2) in the rhizosphere, all kinds of inorganic P forms were negatively correlated with pH. Significant correlation was also observed among the concentrations of dominant forms of inorganic P, C, and N and alkaline phosphatase activities in the rhizosphere. Among the studied species, I. pseudotinctoria showed the most significant effect on enhancing soil available P concentration. The stoichiometric ratios of C:P and N:P were apparently higher in the rhizosphere than the non-rhizosphere, whereas these ratios were far below the ratios commonly observed in Chinese soils. These results indicated that the plant growth effectively affected P fractions possibly by changing pH, C and N concentrations, and alkaline phosphatase activity, in the rhizosphere in copper mine tailings.     

Investigation of Effects on Nutrient Uptake of Humic Acid Applications of Different Forms to Strawberry Plant

Abstract

The aim of this study was to investigate the effect of humic acid in liquid and solid form on uptake of nutrients for strawberry grown under greenhouse conditions. The experiment was designed in randomized block design with four replications for two years. Solid form of humic acid (Agrolig) that contained 85% humic acid was applied in the amounts of 0, 100, 200, 300, and 400 kg/ha before planting. Liquid form of humic acid (Blackjak) that contained 15% humic acid was applied by drip irrigation system at the concentrations of 0, 2500, 5000, 7500, and 10,000 mL/ha/month. Along with humic acid, 200 kg/ha nitrogen (N), 100 kg/ha phosphorus (P₂O₅), and 400 kg/ha potassium (K₂O) was applied by drip irrigation system after transplanting. According to the results, N, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn), and copper (Cu) contents of the leaves were not affected significantly by the applications of solid and liquid humic acid forms. Applied liquid humic acid had a significant effect on the zinc (Zn) content of the leaves causing a decrease in the Zn content. Because of having excessive calcareous soil in the experimental area, uptake of nutrients in strawberry plants was not affected significantly. Applications of humic acid at high concentrations had an inhibitory effect on some of the nutrients.     

Defensive strategies of soil fungi to prevent grazing by Folsomia candida (Collembola)

Fungi represent a major part of the living biomass in the upper soil horizon and serve as an important food source for many soil organisms. We hypothesized that certain mycelial characteristics may serve to protect fungi from grazing. Specifically, this study focused on the influence of poisonous or other repellent metabolites and crystalline structures at the hyphal surface on the feeding preference of the soil microarthropod Folsomia candida Willem. The formation of crystalline structures was studied microscopically and the content of certain metabolites such as amanitin and muscarin was investigated using analytical methods. The feeding preference of F. candida was studied in different in-vitro food choice experiments. Additionally, the palatability of the fungal isolates was estimated by the amount of egg clusters laid by F. candida and by analysing the carbon and nitrogen content of the mycelia. F. candida was repelled by fungal species with toxic metabolites or crystals on their hyphal surface, which indicates that these traits serve as feeding protection. F. candida preferred dark-pigmented fungi. Total number of egg clusters and feeding preference were not correlated. However, insects that fed on fungi without repellent characteristics laid the most eggs. The amount of carbon and nitrogen in the mycelium had no influence on feeding behaviour. We conclude that the content of repellent metabolites and crystalline structures at the hyphal surface are defensive strategies of soil fungi and strongly influence feeding preference of F. candida. Other traits such as palatability were less important. Our results help to explain collembolan feeding behaviour and interactions between soil fungi and Collembola.     

Crop uptake and extractability of cadmium in soils naturally high in metals at different pH levels

Abstract

A greenhouse experiment was conducted for three years to study the effect of different pH levels on metal concentrations in plants and the cadmium (Cd) extractability by DTPA and NH₄NO₃. The soils used were an alum shale (clay loam) and a moraine (loam), which were adjusted to pH levels of 5.5, 6.5, 7.0, and 7.5. Wheat (Triticum aestivum), carrot (Daucus carota L.), and lettuce (Lactuca sativa) were grown as test crops. Crop yields were not consistently affected at increasing soil pH levels. The concentration of Cd in plant species decreased with increasing soil pH in both soils and in all three years. Significant concentration differences between soil pH levels were only seen in wheat and carrot crops. Increasing soil pH also decreased the nickel (Ni) and zinc (Zn) concentrations in plants in the first year crop but the copper (Cu) concentration was not consistently affected by soil pH. The effect of pH was more pronounced in the moraine then the alum shale soil. The DTPA‐and NH₄NO₃‐extractable Cd was decreased with the increasing soil pH and the pH effect was more pronounced with NH₄NO₃ extractable Cd. Both extractants were found equally effective in relation to the Cd concentration in plants in this study.     

Sugarmill effluent effects on growth,photosynthetic pigments and nutrient uptake in wheat seedlings in aqueous vs. soil medium

Germination, seedling growth, concentrations of photosynthetic pigments and nutrient uptake inTriticum vulgare L. (Var. W-H-147) were studied in response to sugarmill effluent application (10% concentration) in aqueous Vs. soil medium. The effluent rich in various nutrients showed particularly high concentration of sodium. Germination was not affected by the effluent treatment. Seedling growth was reduced significantly by the effluent in aqueous medium, but not in soil. The effluent treatment increased the concentrations of various pigments, however, the pigment ratios got changed in the aqueous medium only. The uptake of nitrogen, magnesium and carbon by the seedlings decreased while that of calcium, sodium and phosphorus increased in effluent treated plants, the changes being more marked in aqueous medium except for phosphorus. In the effluent treated plants, uptake of potassium and chloride increased in aqueous medium, hut decreased sharply in soil.     

Short‐term effects of pH and aluminium on mineral nutrition in maize varieties differing in proton and aluminium tolerance

In short‐term (24 h) nutrient solution experiments, the influence of different proton (pH 6.0 and pH 4.3) and aluminium (Al) (0, 20, and 50 μM) concentrations on root and coleoptile elongation, dry weight, and the uptake of selected mineral nutrients was studied in maize (Zea mays L.) varieties that differ in acid soil tolerance under field conditions. The acid‐soil‐tolerant maize varieties, Adour 250 and C525M, proved to be hydrogen (H⁺) ion sensitive, but Al tolerant, while the acid soil tolerant variety BR201F was H⁺ tolerant but Al sensitive. The acid soil sensitive variety HS 7777 was affected by both H⁺ and Al toxicity. The proton‐induced inhibition of root elongation was closely related to the proton‐induced decrease of the specific absorption rates (SAR) of boron (B), iron (Fe), magnesium (Mg), calcium (Ca), and phosphorus (P). In contrast, only the specific absorption rate of B (SARB) was significantly correlated to the Al‐induced inhibition of root elongation. It is concluded, that alterations of nutrient uptake may play an important role in H⁺ toxicity, while at least after short‐term exposure to Al, alterations of Ca, Fe, Mg, or P uptake do not seem to be responsible for Al‐induced inhibition of root elongation. Further attention deserves the Al‐B interaction, moreover taking into account that a highly significant correlation between Al‐induced increase of callose concentration in root tips and Al‐induced decrease of SAR_B could be established.     

Soil compression influences the avoidance behavior of Allonychiurus kimi (Collembola) to cadmium and copper

The behavior of soil organisms inhabiting soil pore spaces can be influenced by soil compression, which can affect their avoidance behavior to pollutants. In this study, we aimed to evaluate the effect of soil compression on the avoidance behavior of Allonychiurus kimi (Collembola) to heavy metals cadmium and copper. Initially, to assess the applicability of the avoidance test guideline of the International Organization for Standardization (ISO) developed for Folsomia candida, we investigated the avoidance behavior of A. kimi to cadmium and copper in an artificial soil with a loose structure (bulk density of 0.25 g cm-3), the porous texture of which was sufficiently loose to enable A. kimi to move between pore spaces. The effect of soil compression on the avoidance behavior of A. kimi to both metals was evaluated in compressed soil (bulk density of 0.64 g cm^-3) with a uniformly compressed soil surface, and avoidance behavior was investigated at 24-h intervals over a 120-h period. Given that A. kimi is unable to burrow into compressed soil, the compressed soil test can minimize the effects of differences in soil factors, such as soil porosity and bulk density, on the behavior of this collembolan. In the artificial soil, a statistically significant avoidance behavior of A. kimi was observed at cadmium and copper concentrations greater than 50 and 200 mg kg^-1, respectively, thereby indicating the applicability of the ISO avoidance test guidelines for A. kimi. When compared at the same exposure time point, the avoidance response to both metals in compressed soil was less sensitive than that in uncompressed soil. In addition, we observed differences in the effects of metals on avoidance response in the compressed soil over time, with the effect of cadmium increasing with time and the effect of copper showing the opposite trend. Overall, we found that soil compression can affect the avoidance behavior of A. kimi to cadmium and copper, and we discussed the advantages and limitations of using compressed soil for assessments of pollutant toxicity.     

Growth and Metal Accumulation of Mycorrhizal Sorghum Exposed to Elevated Copper and Zinc

Arbuscular mycorrhizal fungi (AMF) alter heavy metal acquisition by higher plants and may alter plant response to soil-contaminating heavy metals. Two communities comprised of Glomus intraradices and G. spurcum were investigated for their influence on copper (Cu) and zinc (Zn) resistance of Sorghum bicolor. One community was isolated from a Cu- and Zn-contaminated soil (AMF-C) and one consisted of isolates from non-contaminated soil (AMF-NC). Non-mycorrhizal (NM) sorghum plants were also included. The two community ecotypes differed in their capacity to protect sorghum from Cu and Zn toxicity and exhibited differential metal uptake into hyphae and altered heavy metal uptake by roots and translocation to plant shoots. AMF-C reduced Cu acquisition under elevated Cu conditions, but increased Cu uptake and translocation by sorghum under normal Cu conditions, patterns not exhibited by AMF-NC or NM plants. Hyphae of both fungal ecotypes accumulated high concentrations of Cu under Cu exposure. AMF-C exhibited elevated hyphal Zn accumulation and stimulated Zn uptake and translocation in sorghum plants compared to AMF-NC and NM plants. Differences in metal resistance between fungal treatments and between mycorrhizal and non-mycorrhizal plants were not related to differences in nutrient relations. The enhanced Cu resistance of sorghum and altered patterns of Cu and Zn translocation to shoots facilitated by AMF isolated from the metal-contaminated soil highlight the potential for metal-adapted AMF to increase the phytoremediation potential of mycotrophic plants on metal-contaminated environments.     

Physiology of phytoplankton in relation to metal concentration Effect of cadmium on Scenedesmus bijugatus and Nitzschia palea

The effect of Cd at sublethal concentrations on pure cultures of S. bijugatus and N. palea was studied with special reference to their physiology during exponential growth phase. Photosynthetic productivity, respiration, pH, biomass, pigments, carbohydrate, protein, lipid as well as nutrient uptake were selected to study the comprehensive effect of the metal. The physiology of the species was significantly affected by Cd during the exponential growth phase and altered the ratio of carbohydrate, protein and lipid in the test species.     

Species-specific impacts of collembola grazing on fungal foraging ecology

Fungi are primary agents of organic matter decomposition in forests. Although invertebrate grazing affects fungal biomass and morphology, the species-specific consequences of these interactions are little understood. Using three collembola species (Folsomia candida, Protaphorura armata, Proisotoma minuta) we employed a multi-trophic approach to investigate the individual effects of invertebrate grazing on four species of saprotrophic basidiomycete fungi growing in two species (one fungus: one collembola) soil microcosms. We studied these effects at three trophic levels: the rate of wood decay brought about by the fungi was assessed; fungal growth was characterized across multiple time points using a range of image analysis parameters (radial extension, hyphal coverage, fractal dimension); and collembola abundance was determined at the end of the experiment. Collembola species had different impacts both within and across fungal species; F. candida had the greatest effect on fungal mycelia whereas P. armata often had little impact. Fungal species varied in their resilience to grazing; all collembola species modified Phanerochaete velutina and Hypholoma fasciculare morphology, that of Resinicium bicolor was only markedly affected by F. candida, and effects on Phallus impudicus were negligible. In the case of H. fasciculare, these grazing effects translated into effects on the rate of fungus-induced wood decay: F. candida and P. armata, but not P. minuta, reduced wood decay rate compared to ungrazed controls. Rate of wood decay was unaffected in the other three fungal species. Changes in collembola population size were generally consistent across fungal species, with each species achieving a greater abundance on P. velutina than on H. fasciculare and P. impudicus. The collembola species did, however, respond differently to R. bicolor, with F. candida being more successful than P. armata. Our study suggests that a wide range of impacts can occur during fungus–collembola interactions, and that caution should be exercised when treating saprotrophic fungi and mycophagous collembola as uniform functional components.     

蚓粪对黑麦草吸收污染土壤重金属铜的影响

在长江冲积物形成的高沙土中加入CuSO4.5H2O模拟土壤污染,使Cu污染浓度分别为200、400、600 mg kg-1,并设置加蚓粪(15%)和加原土(15%)处理,二处理各设种植黑麦草(Lolium multiflorum)和不种黑麦草培养试验,研究蚓粪对黑麦草生长及对Cu吸收的影响,以揭示蚓粪在Cu污染土壤植物修复中的作用。结果表明:蚓粪显著增加了黑麦草的地上部和地下部的生物量(p<0.001**)以及根系的长度、表面积、体积和根尖数(p<0.05*),在Cu浓度为200 mg kg-1时促进作用最大;蚓粪还显著提高了黑麦草地上部Cu的浓度及累积量,但显著降低了地下部的Cu浓度(p<0.05*),而对地下部的铜累积量没有影响,显示蚓粪能促进Cu从根系向地上部的运移及在地上部的富集。通过对土壤的pH和Cu的形态特征分析,发现种植黑麦草处理降低了土壤的pH并增加了可交换态铜的含量,而且这种作用在加入蚓粪后更加明显。推测蚓粪主要通过促进黑麦草根系的生长和活性而影响根系周围环境,提高重金属铜的生物有效性进而增加植物对铜的吸收。     

Effects of earthworms on Zn fractionation in soils

Laboratory incubation experiments were conducted to examine the effect of earthworm (Pheretima sp.) activity on soil pH, zinc (Zn) fractionation and N mineralization in three soils. No Zn uptake by earthworms was observed. Zinc addition decreased pH of red soil (soil 1) and hydragric paddy soil (soil 3) by 0.5 and 0.2 unit, respectively, but had no effect on alluvial soil (soil 2). The effect of Zn on soil pH was possibly due to a specific adsorption mechanism between Zn and oxides. Earthworm activity significantly decreased the pH of the red soil, a key factor affecting Zn solubility, but not of the other two soils. Earthworm activity significantly increased DTPA-Zn (DTPA-extractable) and OxFe-Zn (NH₂OH-HCl-extractable) in the red soil, but had little effect on other fractions. In the alluvial soil, earthworm activity significantly increased OxFe-Zn but decreased organic-Zn (organic-associated Zn). In the hydragric paddy soil, earthworm activity significantly increased MgCl₂-Zn (MgCl₂-extractable) and organic-Zn. The level of CaCl₂-extractable Zn in all three soils was not affected by earthworm activity. Nitrogen mineralized as a result of earthworm activity was equivalent to 110, 120 and 30 kg N ha^-1 in soils 1, 2 and 3, respectively. Zinc added at rates less than 400 mg Zn kg^-1 did not seem to affect the activity of N-mineralizing microorganisms. The present results indicated the possibility of increasing the metal bioavailability of relatively low level metal-contaminated soils, with a higher organic matter content, by earthworm inoculation.     

Recovery of reproduction after drought in the soil living Folsomia candida (Collembola)

Soil dwelling (euedaphic) Collembola have evolved to live in soil pores where the atmosphere is saturated with water vapour. Here we show that reproduction in the euedaphic Folsomia candida ceases during drought where soil water potentials are lower than −7 bar (∼99.4% RH). Recovery of the moulting cycle after cessation of drought showed increasing delay with increasing previous drought pressure. However, reproduction was rapidly resumed. Only in F. candida recovering from the most severe drought (−55 bar, 96% RH) was the time lapse between drought and resumed reproduction significantly different from the control (99.4% RH). Furthermore, the final numbers of eggs were unaffected by the degree of drought exposure. Hence, these results suggest that while even very mild drought will stop the reproductive cycle, subsequent recovery is rapid and complete.     

Ecotoxicological assessment of organic wastes using the soil collembolan Folsomia candida

The reproduction test with the collembolan Folsomia candida is used as a tool to evaluate the ecotoxicological potential of organic wastes currently applied to soil. Seven organic wastes (dewatered sewage sludges, thermally dried sewage sludges, composted sewage sludges, and a thermally dried pig slurry) were tested. These wastes had different origins, treatments, and pollutant burdens, and were selected as a representative sample of the wide variety of wastes currently generated. F. candida showed varied sensitivity depending on the waste, but also depending on the endpoint assessed. Reproduction was more sensitive than survival, although no correlations between reproduction and physico-chemical parameters and pollutant burden could be found. On the other hand, mortality was directly related to the lack of stability of wastes, probably reflecting the toxicity of end-products such as ammonium. Body length was not shown to be a sensitive endpoint for waste testing, as it was neither affected nor even stimulated by waste concentrations.Organic matter, pH, and electrical conductivity varied with waste concentration in soil-waste mixtures, although their effect on collembolan performance was expected to be low and part of the complex effect exerted by wastes when applied to real soils. Selection of the water content is the most problematic aspect in waste testing, as it may affect the performance of test organisms. In this study, a qualitative approach for water content selection in waste testing was considered to be the most suitable.Treatment of wastes affected composition and toxicity. Composting of sewage sludge increased its stability, compared to the initial sludge, but decreased its non-persistent organic pollutant burden and toxicity. On the other hand, thermally dried wastes from sludge and pig slurry displayed high toxicity, mainly attributable to their low stability. The results from the study indicate the inability of chemical methods to predict the effects of complex mixtures on living organisms with respect to ecotoxicity bioassays, but also the need for stabilization treatments of organic wastes prior to their reuse in soils.