Soil additives immobilising heavy metals in contaminated soils

Addition of iron oxides, lime, clay minerals and other substances can be used to decrease the plant availability of toxic heavy metals such as Pb, Zn, and Cd. Extractability and consequently plant concentrations may be reduced in some cases by more than 50%. The assessment of remediation processes is supported by biomonitoring methods in the field with Plantago lanceolata and in the greenhouse by barley test experiments, in combination with extraction by ammonium nitrate.

Host Plant Availability and Nest-Site Selection of the Social Spider Stegodyphus dumicola Pocock, 1898 (Eresidae)

An animals’ habitat defines the resources that are available for its use, such as host plants or food sources, and the use of these resources are critical for optimizing fitness. Spiders are abundant in all terrestrial habitats and are often associated with vegetation, which may provide structure for anchoring capture webs, attract insect prey, or provide protective function. Social spiders construct sedentary communal silk nests on host plants, but we know little about whether and how they make nest-site decisions. We examined host plant use in relation to host plant availability in the social spider Stegodyphus dumicola Pocock, 1898 (Eresidae) across different arid biomes in Namibia and analysed the role of host plant characteristics (height, spines, scent, sturdiness) on nest occurrence. Host plant communities and densities differed between locations. Spider nests were relatively more abundant on Acacia spp., Boscia foetida, Combretum spp., Dichrostachys cinerea, Parkinsonia africana, Tarchonanthus camphoratus, and Ziziphus mucronatus, and nests survived longer on preferred plant genera Acacia, Boscia and Combretum. Spider nests were relatively more abundant on plants higher than 2 m, and on plants with thorns and with a rigid structure. Our results suggest that spiders display differential use of host plant species, and that characteristics such as rigidity and thorns confer benefits such as protection from browsing animals.

Population density and plant availability interplay to shape browsing intensity by roe deer in a deciduous forest

Browsing damage in forests relies on a complex interaction between herbivore density and both forest understory composition and relative availability. Although variation in the amount of browsed twigs is sometimes used to assess abundance of large herbivores, the potential confounding effect of resource availability on this relationship has not yet been investigated. To fill the gap, we measured how browsing intensity of the woody plants varied in response to changes in both roe deer (Capreolus capreolus) abundance and vegetation availability from an intensive long-term monitoring. We estimated plant availability and consumption by roe deer from a modified Aldous method throughout a 14 yearlong period during which we experimentally manipulated population density. The functional response was strongly non-linear and density-dependent. When plant availability was low (< 12.5%), browsing intensity strongly increased with plant availability with an increasing rate with roe deer density, whereas beyond this threshold, browsing intensity slightly increased with both plant availability and population density in an additive way. Thus, forest susceptibility to browsing increases with increasing competition for food, especially when plant availability is low. Moreover, the interplay between browsing intensity and population density at low plant availability prevents the use of browsing intensity to monitor roe deer abundance when plant availability is low. Our findings provide clear evidence that relying on key ecological concepts such as functional responses improves the accuracy of management tools when monitoring changes of the herbivore-plant system over time.

Site-Effects Dominate the Plant Availability of Nutrients under Salix Species during the First Cutting Cycle

Fast-growing willows (Salix spp.) provide alternative sources of renewable energy generation, but need an adequate nutrient availability in the soil for high biomass production. In general, species mixtures can be more nutrient-efficient than pure cultures, but this is scarcely known for Salix spp. Therefore, this study evaluates the nutrient availability and P mobilization under two willow species, Salixdasyclados var. ‘Loden’ and S. schwerinii × viminalis var. ‘Tora’, grown as pure and mixed cultures at non-fertilized former arable sites in Germany (Stagnic Cambisol) and Sweden (Vertic Cambisol). The plant availability of potassium (K), magnesium (Mg) and phosphorus (P) and soil phosphatase activities in the topsoil were measured in spring of the year of planting (initial) and under 4 years-old stocks (one year after the first 3-year cutting cycle). The initial plant availability of the nutrients significantly differed between the sites and the two sampling dates at both sites. The plant availability of K and Mg was optimal to high at both sites and sampling dates, but rather low for P (after 4 years ≤5 mg P 100 g−1 soil). The plant-available P and K content in soil significantly decreased within the 4 years of willow growth at both sites. The acid and alkaline phosphatase activity in the soil of the German site (Rostock) was significantly lower after 4 years of willow growth, but differed not significantly between the two sampling dates at the Swedish site (Uppsala). Higher activity of acid phosphatase compared to alkaline phosphatase was recorded in the soils at both test sites based on the site-specific soil pH (<7). The slight decrease of plant availability of P after 4 years of Salix growth in pure culture differed not significantly between the different species. Mixed growth did not decrease the plant availability of P within this period, although no significant difference in the biomass production of pure and mixed growth was observed. This was valid at both sites, and therefore, seems independent of the site-specific differences in soil and climate conditions. The general validity of the assumptions should be tested also for other species mixtures and soil conditions in the future before site-adapted growth designs can be recommended in biomass production of Salix.

Double-countershading as a means of camouflage in larvae of Orange-tip Anthocharis cardamines (Linnaeus, 1758) (Lepidoptera: Pieridae)

In Shaw & Otto (2020), Shaw described larvae of the butterfly, Orange-tip Anthocharis cardamines (Linnaeus, 1758), that were visually obvious yet apparently immune to bird predation. He speculated that mustard oils in the foodplants may render them distasteful to birds so that being conspicuous is of little consequence, allowing them to bask in sunshine possibly to aid digestion. In contrast, I argue that in certain lighting conditions larger larvae of Orange-tip can be very well camouflaged. These two different defence mechanisms are not mutually exclusive and each may come into play under different conditions of lighting, larval age and/or food-plant availability. For disguise the larvae make use of double-countershading in what Süffert (1932) called the 'two-surface effect'. Here I briefly describe its mechanism along with that of the better-known ordinary (single) countershading. Photographs are shown of both.

Plant Availability of Magnesium in Typical Tea Plantation Soils

Background and Aims: Magnesium (Mg) fertilizer has been proved to play an important role in improving the yield and quality of tea. However, plant availability of Mg, including its use, efficiency, and quality improvement effects, were highly affected by plant species, soil characteristics (nutritional status, etc.), and Mg status (chemical-available, etc.).Methods: Tea plants were pot-cultivated in 12 typical tea plantation soils amended with and without Mg fertilizer. Exchangeable Mg (Ex-Mg) concentration in soils was quantitatively extracted using four extraction solutions (Mehlich-3, BaCl2, CaCl2, and NH4OAC). Plant availability of Mg was evaluated by Mg uptake and its use efficiency, as well as its association with quality components in tea plants.Results: Ex-Mg in soils was extracted most efficiently by Mehlich-3, while Mg concentrations in tea plant tissue were higher correlated with Ex-Mg extracted by CaCl2 than other extraction solutions. Mg fertilizer use efficiency in tea plant varied from 6.08 to 29.56 %, and the effect of Mg application on tea quality improvement and the use efficiency of Mg fertilizer both negatively correlated with total Mg concentration (r = −0.94 and −0.63, respectively) and nitrogen (N) level (r = −0.61 and −0.51, respectively) in soils prior to tea plant cultivation.Conclusions: CaCl2 could be recommended for plant-available Mg extraction in tea plantation soil, and Mg fertilizer use efficiency could be affected and predicted by total N and Mg status in soils prior to tea plant cultivation, providing a potential theoretical for the guidance of Mg fertilization for tea yield and quality improvement in tea plantation management.

Mixed Growth with Weeds Promotes Mycorrhizal Colonization and Increases the Plant-Availability of Phosphorus under Maize (Zea mays L.)

(1) Background: Weed control decreases the competition for nutrients, but also the potential of increased phosphorus (P) mobilization in soils caused by higher plant diversity. (2) Methods: Impacts of weed species under maize on mycorrhizal colonization and plant-availability of P were investigated in two pot experiments. Plant traits and P mobilization were tested in weed-free maize and in mixed growth with six annual weed species. (3) Results: Growth of maize decreased in treatments with weeds, while P concentrations in its shoots increased in mixed growth with C. album, E. crus-galli and P. convolvulus. Mycorrhizal colonization of maize without weeds was low (<20% of root length), but increased in mixed growth with C. album, E. crus-galli and V. arvensis up to 40%. The activities of Pmobilizing hydrolytic enzymes (phosphatases, ß-glucosidase) and plant-availability of P were occasionally higher under mixed growth with weeds. The dimension of weed impacts on P cycling under maize differed significantly between both experiments. (4) Conclusions: Weeds potentially promote P mobilization and mycorrhizal colonization under maize, but this impact is not guaranteed. The weed-based improved P supply of maize should be defined under field conditions to allow a controlled weed tolerance in maize cropping systems.

Comparison of thermochemical treatment of sewage sludge ash with sodium sulphate in laboratory-scale and pilot-scale experiments

There is an ongoing debate on European scale concerning the criticality of phosphorus. In Switzerland and Germany, phosphorus recovery from phosphorus-rich waste streams will become obligatory. Sewage sludge ash is rich in phosphorus and may become an important secondary feedstock. Thermochemical treatment of sewage sludge ash with sodium sulphate under reducing conditions was shown to remove heavy metals from the solid product and produce the fully plant available crystalline phase CaNaPO4. Pilot-scale experiments in a rotary kiln were carried out at temperatures between 750 and 1000 °C and were compared to laboratory-scale experiments with crucibles. Process upscaling was successfully demonstrated but a series of differences were noticed: In comparison to laboratory-scale, solubility of phosphorus in samples from pilot-scale experiments was lower at all chosen treatment temperatures because of shorter retention time and incomplete decomposition of sodium sulphate. X-ray diffraction analysis revealed remaining phase fractions of whitlockite (Ca3-x(Mg,Fe)x(PO4)2) and sodium sulphate from the starting materials in products and thus indicated incomplete reaction. In contrast to the results of laboratory-scale experiments, the crystalline phase CaNaPO4 was clearly absent in the products from the rotary kiln but instead a Mg-bearing phase (Ca,Mg)NaPO4 was formed. Laboratory-scale experiments confirmed (Ca,Mg)NaPO4 is an intermediate phase between whitlockite and CaNaPO4. However, both crystalline phases are characterized by high plant availability. It was shown that heavy metal removal increased at higher temperatures whereas solubility and thus plant availability of phosphorus already reached its maxima at temperatures of 950 °C in pilot-scale and 875 °C in laboratory-scale experiments.

Nitrogen fertilizer value of animal slurries with different proportions of liquid and solid fractions: A 3-year study under field conditions

The plant availability of manure nitrogen (N) is influenced by manure composition in the year of application whereas some studies indicate that the legacy effect in following years is independent of the composition. The plant availability of N in pig and cattle slurries with variable contents of particulate matter was determined in a 3-year field study. We separated cattle and a pig slurry into liquid and solid fractions by centrifugation. Slurry mixtures with varying proportions of solid and liquid fraction were applied to a loamy sand soil at similar NH4+-N rates in the first year. Yields and N offtake of spring barley and undersown perennial ryegrass were compared to plots receiving mineral N fertilizer. The first year N fertilizer replacement value (NFRV) of total N in slurry mixtures decreased with increasing proportion of solid fraction. The second and third season NFRV averaged 6.5% and 3.8% of total N, respectively, for cattle slurries, and 18% and 7.5% for pig slurries and was not related to the proportion of solid fraction. The estimated net N mineralization of residual organic N increased nearly linearly with growing degree days (GDD) with a rate of 0.0058%/GDD for cattle and 0.0116%/GDD for pig slurries at 2000–5000 GDD after application. In conclusion NFRV of slurry decreased with increasing proportion of solid fraction in the first year. In the second year, NFRV of pig slurry N was significantly higher than that of cattle slurry N and unaffected by proportion between solid and liquid fraction.