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Soil micronutrients are capital for the delivery of ecosystem functioning and food provision worldwide. Yet, despite their importance, the global biogeography and ecological drivers of soil micronutrients remain virtually unknown, limiting our capacity to anticipate abrupt unexpected changes in soil micronutrients in the face of climate change. Here, we analyzed >1300 topsoil samples to examine the global distribution of six metallic micronutrients (Cu, Fe, Mn, Zn, Co and Ni) across all continents, climates and vegetation types. We found that warmer arid and tropical ecosystems, present in the least developed countries, sustain the lowest contents of multiple soil micronutrients. We further provide evidence that temperature increases may potentially result in abrupt and simultaneous reductions in the content of multiple soil micronutrients when a temperature threshold of 12–14°C is crossed, which may be occurring on 3% of the planet over the next century. Altogether, our findings provide fundamental understanding of the global distribution of soil micronutrients, with direct implications for the maintenance of ecosystem functioning, rangeland management and food production in the warmest and poorest regions of the planet. [ABSTRACT FROM AUTHOR]

Dryland soils provide different societal and environmental services, such as food supply and biodiversity support. In Europe, most of the dryland areas are devoted to agriculture. In the next decades, both European and worldwide drylands are expected to suffer with increased intensity due to the expected climate change‐derived rise in aridity. Many studies have focussed on aridity‐induced changes in major nutrients in drylands, but little is known of the impact of environmental and biogeochemical factors on micronutrients with critical roles in life, and as inorganic contaminants with ecotoxicological implications. We analysed and explored drivers of total and available concentrations of micronutrients (Co, Cu, Fe, Mo, Mn, Ni and Zn) and contaminants (As, Cd and Pb) in 148 soil samples collected from European drylands covering a wide range of aridity and of other geochemical parameters. The availability of micronutrients increased with their total content, decreased with pH and was enhanced by organic C content. Aridity decreased the availability of Fe, a key element in human diet. Our findings also highlight the scarcity of this micronutrient in European drylands, as well as of some other important micronutrients like Zn and Mo in agricultural soils. Total content was the main driver of the availability of Cd and Pb, and organic matter exerted synergistic effects on contaminant release. Our data show the need for precise management practices to be incentivised by agricultural and environmental policies in order to ensure micronutrient supply and avoid contamination, thus maintaining adequate levels of agricultural productivity and simultaneously preserving dryland ecosystems. Highlights: Drylands are important for food production in Europe and sensitive to climate change.The occurrence of metals in European Union dry soils and the drivers influencing them were studied.Some micronutrients (Fe, Mo and Zn) were scarce while contaminants were abundant.SOC, pH and clays were the main drivers of element availability; aridity reduced Fe.Agricultural practises are needed to ensure nutrient supply and prevent contamination. [ABSTRACT FROM AUTHOR]

The biogeochemical cycling of multiple soil elements is fundamental for life on Earth. Here, we conducted a global field survey across 16 chronosequences from contrasting biomes with soil ages ranging from centuries to millions of years. For this, we collected and analysed 435 topsoil samples (0–10 cm) from 87 locations. We showed that high levels of topsoil element coupling, defined as the average correlation among nineteen soil elements, are maintained over geological timescales globally. Cross‐biome changes in plant biodiversity, soil microbial structure, weathering, soil pH and texture, and mineral‐free unprotected organic matter content largely controlled multi‐element coupling. Moreover, elements with heavier atomic mass were naturally more decoupled and unpredictable in space than those with lighter mass. Only the coupling of carbon, nitrogen and phosphorus, which are essential to life on Earth, deviated from this predictable pattern, suggesting that this anomaly may be an undeniable fingerprint of life in terrestrial soils. [ABSTRACT FROM AUTHOR]

The contamination of soils and waters with organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), affect a large number of sites worldwide that need remediation. In this context soils amendments can be used to immobilise PAHs while maintaining soil functioning, with biochar being a promising amendment. In this experiment, phenantrene (Phe) was used as a frequent PAH contaminating soils and we studied the effect of three biochars at 1% applications to three different substrates, two agricultural topsoils and pure sand. We evaluated the changes in soil properties, sorption-desorption of Phe, and mineralisation of Phe in all treatments. Phe in pure sand was effectively sorbed to olive pruning (OBC) and rice husk (RBC) biochars, but pine biochar (PBC) was not as effective. In the soils, OBC and RBC only increased sorption of Phe in the silty soil. Desorption was affected by biochar application, RBC and OBC decreased water soluble Phe independently of the soil, which may be useful in preventing leaching of Phe into natural waters. Contrastingly, OBC and RBC slightly decreased the mineralisation of Phe in the soils, thus indicating lower bioavailability of the contaminant. Overall, biochar effects in the two tested soils were low, most likely due to the rather high soil organic C (SOC) contents of 2.2 and 2.8% with Koc values in the same range as those of the biochars. However, OBC and RBC additions can substantially increase adsorption of Phe in soils poor in SOC. [ABSTRACT FROM AUTHOR]

Biochar is a promising immobilizing agent of trace elements (TEs) in contaminated soils. However, several contradictory results have been reported regarding the potential of biochar to immobilize arsenic (As), chromium (Cr), and nickel (Ni) in contaminated soils. We conducted a meta-analysis on the published papers since 2006 until 2019 to examine the effects of biochar on the chemical (im)mobilization of As, Cr, and Ni in contaminated soils and to elucidate the major factors that control their interactions with biochar in soil. We synthesized 48 individual papers comprised of a total of 9351 pairwise comparisons and used the statistical tool of Cohen's d as an appropriate effect size for the comparison between means. We found that the application of biochar often increased the As mobilization in soils. Important variables that modulated the biochar effects on As mobilization in soil were pyrolysis temperature and time (ranging between 8 and 16 times when T > 450 °C and t > 1hr), organic matter (7–16 times when SOM<3%) and further site conditions. In contrast to As, biochar efficiently immobilized Cr and Ni in contaminated soils. The extent of the Cr and Ni immobilization was determined by the feedstock (Cr: 7–18 times for agricultural residue-derived biochar; Ni: 13–32 times for woody biomass-derived biochar). Our meta-analysis provides a compilation on the potential of different types of biochar to reduce/increase the mobilization of As, Cr, and Ni in various soils and under different experimental conditions. This study provides important insights on factors that affect biochar's efficiency for the (im)mobilization of As, Cr, and Ni in contaminated soils. While biochar effectively immobilizes Cr and Ni, a proper management of As-polluted soils with pristine biochar is still challenging. This limitation might be overcome by modification of biochar surfaces to exhibit higher surface area and functionality and active sites for surface complexation with TEs. [Display omitted] • Biochar immobilized Cr and Ni in soil. • Biochar produced >450 °C exhibited high As mobilization in soils. • The best feedstock for Ni immobilization was wood. • The worst feedstock for Ni immobilization was agricultural residues and sewage sludge. • Biochar for Cr and Ni immobilization was efficient in acidic humus poor soils. [ABSTRACT FROM AUTHOR]

Urban soils are at the interface between land and people and provide a wide variety of important ecosystem services to highly populous areas. The aims of this soil survey were (1) to measure the bulk density, carbon (C) storage and pH of surface soils (0–15 cm depth) from public spaces (parks and road verges) in the city of Liverpool, UK, and (2) to determine the likely impact of these master variables on heavy metal concentrations (As, Cd, Cu, Pb and Zn). The bulk densities and organic matter contents varied considerably in the predominantly sandy textured soils within the city boundary, resulting in diverse C densities from 1–10 kg C m2. Organic carbon formed the majority of the labile, water-soluble and extractable C pool in these soils, a fact not easily elucidated from their organic matter or C content alone. The copper and lead concentrations in the sampled soils were correlated with organic matter and organic carbon in water-extracts. Cadmium and zinc appeared to be dependent only on soil pH, whilst arsenic was related positively to organic matter, but negatively to pH. Interrelationships, and hence synonymous distributions, of all metal(loid)s existed, but were strongest between Cu and As, and Cu and Pb. These results suggest that the diverse bulk densities, and hence carbon storage, of the urban soils surveyed influenced the dispersal of metals and arsenic. [ABSTRACT FROM AUTHOR]

Current intensive agricultural practices, although highly successful in terms of production, have been found to be environmentally unsustainable. One of the crucial approaches to increase agricultural sustainability is the recycling of organic wastes, since these materials often contain many beneficial nutrients for soil and agriculture. Recently, pyrolytic conversion of biodegradable waste into charred material has gained global attention as an amendment to recycle nutrients while improving soil health. Increasing interest in the beneficial applications of pyrolyzed biomass has expanded multidisciplinary areas for science and engineering. The fertilizers used in this study were prepared by pyrolyzing mixtures of two abundant residues in Mediterranean areas: grape seeds and sewage sludge, in different proportions (100% GS, 75% GS-25% SS, 50% GS-50% SS, 25% GS-75% SS, 100% SS). In addition, fresh sludge was mixed with pyrolyzed grape seeds and included as an additional treatment. In this study, the positives and negatives of the application of biochars on agronomic potential and environmental risk have been addressed, taking into account P, Zn, Cu, Fe, As and Cd. In order to choose the best mixture, it is necessary to find a compromise between maximizing the beneficial elements that are translocated to the plant crop, as well as reducing the elements that are leached. Results of a 6-week greenhouse study indicated that the unpyrolyzed sludge mixture contained the largest amount of available nutrients Fe, Cu and P. In agreement, this treatment mixed with a Chromic Luvisol soil (40 ton/ha) increased the uptake of these elements in corn (Zea mays L.—LG ambitious). The yield also increased by 60% in this treatment. However, this mixture also contained more contaminants (As, Cd) which were extracted with Ammonium Bicarbonate-DTPA. According to our results, the treatments where grape seeds and sewage sludge were mixed at 50% and then pyrolyzed exhibited the optimal compromise between efficiency (nutrients uptake) and tolerable levels of potentially toxic elements in leachates. [ABSTRACT FROM AUTHOR]