Do aphids biomagnify Cd and Zn as a defence against predation?

The results of a study on sewage sludge application to agricultural soil have led us to propose that recycling sewage sludge can affect the biological control of grain aphids. This, we suggest, is due to the biomagnification of trace metals in the aphid presenting potentially toxic concentrations to predators

Forest humus type governs heavy metal accumulation in specific organic matter fractions

Soils have the potential to accumulate heavy metals and the capacity to do so is strongly related the properties of each soil. Soil organic matter is a key factor in the retention, release, and bioavailability of heavy metals, and here we have determined the accumulation of heavy metals in various types of humus in the Rybnik Forest District in southern Poland. In a novel approach, we analyzed relationships between heavy metals within soil organic matter fractions and evaluated the role of organic fractions in mediating metal mobility. Specifically, we tested whether (i) the type of forest humus determines the heavy metal accumulation; (ii) heavy metals accumulation is associated with soil organic matter fractions; and (iii) heavy metals have an inhibitory influence on biochemical properties especially enzymes activity in different humus types. Four types of humus were sampled (mor, moder, moder-mull, mull), physically fractioned, and a number of chemical and biochemical properties were analyzed. Calculated geo-accumulation index (Igeo) and enrichment factor (EF) confirmed soil pollution with Cd and Pb. The type of humus differed in the accumulation of heavy metals, which is associated to the variable concentration of organic matter remaining at each decay class. We found no relationship between enzymatic activity and heavy metals concentration except for a positive correlation between urease activity and nickel concentration. Considering wider evidence, we propose a biogeochemical link between nickel deposition and the production of soil-borne urease in these forest soils

The effect of sewage sludge application to an agricultural soil on the fecundity of the Rose Grain aphid (Metopolophium dirhodum).

A pot trial was used to assess the effect of amending soil with sewage sludge on the number of offspring produced by individual Rose Grain Aphids. Results demonstrated that the highest application rate (100 t.d.s. ha-1) could significantly decrease the number of offspring produced by the aphid

Soil chemical and physical constraints to pasture productivity on rehabilitated land after bauxite mining

The reconstruction and rehabilitation of soil profiles to facilitate sustainable land use as a pasture, requires careful planning and management. Pastures are among the most common form of land rehabilitation after mining, but the productivity of these pastures is less than that of comparable unmined land. Here we assessed the soil properties and pasture production on recently rehabilitated farmland after bauxite mining, which are considered to have diminished productivity in comparison to adjacent unmined grassland. This was to understand the limitation to achieving levels of soil fertility, pasture productivity and sustainability similar to those of the pre-mined landscapes. After comparing soil pit profile descriptions, we assessed several soil and plant parameters to identify the constraints to pasture growth. Several edaphic parameters differed between unmined and rehabilitated soils, including pH, salinity, particle size distribution, soil strength, soil organic carbon and cation exchange capacity. Both rehabilitated and unmined areas had some deficiencies in plant available nutrients in both topsoils and subsoils. Many of the edaphic parameters that showed significant differences were likely due to the mixing of materials during excavation, handling and re-spreading as part of the mining and rehabilitation process. The pasture plants also exhibited different responses between rehabilitated and unmined soils. Root mass penetration through the rehabilitated profiles was generally less than the unmined profiles. Differences in pasture dry matter production were identified between the mined and unmined areas. No significant difference was found in pasture species composition on the rehabilitated sites. In summary, no single constraint to pasture production on the rehabilitated land was identified. However, the handling and mixing of the soil materials leading to the creation of impenetrable zones may be an important aspect. In addition, organic matter concentrations remain low in rehabilitated topsoils and fertile topsoils were likely diluted through the disturbance and the profile reconstruction process. These three factors may be attributed to the underlying cause of reduced pasture production

Tolerance, toxicity and transport of Cd and Zn in Populus trichocarpa

Metal inputs to terrestrial ecosystems are of great concern due their toxicity to biota, especially for elements with no biological function such as cadmium. Fast-growing trees such as poplars may have potential in phytoremediation schemes. We assessed accumulation, metal partitioning, gene expression (Pt-HMA4) and overall tolerance to, and interaction between, cadmium (Cd) and zinc (Zn) in Populus trichocarpa ‘Trichobel’. We predicted that Zn would have an antagonistic effect in Cd accumulation and anticipated some level of tolerance to these metals. Poplars were grown in sandy substrate under different metal applications, ranging from 1 to 243 mg kg−1 Cd; or 30 to 7290 mg kg−1 Zn; and also two combined treatments: 27 mg kg−1 Cd with 90 or 270 mg kg−1 Zn. Growth parameters and metal contents in shoots and roots were determined. Transcriptional levels of the Pt-HMA4 gene were assessed in roots and leaves. P. trichocarpa showed a surprisingly high tolerance to Cd, with root biomass being affected only at the highest doses applied. Metals accumulated mainly in roots (up to 6537 mg kg−1 Cd and 21,500 mg kg-1 Zn), root-to-shoot translocation peaked at the 9 mg kg−1 dose for Cd (41%) and 90 mg kg−1 for Zn (40%). At high Cd/Zn applications, expression of Pt-HMA4 in roots decreased significantly. Contrary to the initial presumption, Zn addition increased Cd uptake, reaching hyperaccumulator-like concentrations in shoots (≥100 mg kg−1 Cd). Differential root-to-shoot partitioning has a major role in Cd tolerance in P. trichocarpa; partly by down-regulating the Pt-HMA4 gene in roots. Zn addition promoted high Cd uptake without any detriment to plant growth. P. trichocarpa was tolerant to extreme Cd concentrations, offering a great potential to be used in phytoremediation techniques for stabilization/extraction of Cd from soils contaminated by both Cd and Zn

Cd and Zn interactions and toxicity in ectomycorrhizal basidiomycetes in axenic culture

Background. Metal contamination in soils affects both above- and belowground communities, including soil microorganisms. Ectomycorrhizal (ECM) fungi are an important component in belowground community and tolerant strains have great potential in enhancing plant-based remediation techniques. We assessed cadmium and zinc toxicity in five ECM species in liquid media (Hebeloma subsaponaceum; H. cylindrosporum; H. crustuliniforme; Scleroderma sp.; Austroboletus occidentalis) and investigated the potential of Zn to alleviate Cd toxicity. Due to highly divergent results reported in the literature, liquid and solid media were compared experimentally for the first time in terms of differential toxicity thresholds in Cd and Zn interactions. Methods. A wide range of Cd and Zn concentrations were applied to ectomycorrhizal fungi in axenic cultures (in mg

Too much of a good thing: phosphorus over-fertilisation in rehabilitated landscapes of high biodiversity value

Fertilisers supply essential nutrients lacking in post-mining substrates in nearly all terrestrial rehabilitation schemes. Regulators typically require the rapid revegetation of post-mining lands as an indicator of early rehabilitation success, mapping to perceived pathways of successful ecosystem recovery. However, we will show how this approach can lead to poorer outcomes in terms of vegetation composition and potentially, long-term issues in ecosystem biogeochemistry. Many mines exist in remote areas and on highly weathered, ancient, nutrient poor soils. Examples of these are the Fynbos of South Africa, the western and northern forests of Australia, the Campos rupestres of South America, and many tropical areas. Typically, restoration requirements in these areas require the return of a native vegetation community that existed prior to mining. This is particularly common for surface strip mining where large areas of land are cleared of vegetation annually. In this paper, we show how, where, and why over-fertilisation can occur. Based on examples from western and northern Australia, we demonstrate that the application of phosphoruscontaining fertilisers to these nutrient depleted soils can result in long-term elevated soil phosphorus, with species-specific negative impacts on plant health and growth. We show the rehabilitation benefits that can be gained by judicious fertilisation in terms of vegetation community structure and ecosystem development. Finally, to assess where these findings may have wider applicability, we identify further global regions with nutrient depleted soils, high plant diversity, and current or prospective strip mining operations