Improving the relationship between soil characteristics and metal bioavailability by using reactive fractions of soil parameters in calcareous soils

Metallic micronutrients are associated with the structure and function of the soil microbiome

The relationship between metallic micronutrients and soil microorganisms, and thereby soil functioning, has been little explored. Here, we investigate the relationship between metallic micronutrients (Fe, Mn, Cu, Zn, Mo and Ni) and the abundance, diversity and function of soil microbiomes. In a survey across 180 sites in China, covering a wide range of soil conditions the structure and function of the soil microbiome are highly correlated with metallic micronutrients, especially Fe, followed by Mn, Cu and Zn. These results are robust to controlling for soil pH, which is often reported as the most important predictor of the soil microbiome. An incubation experiment with Fe and Zn additions for five different soil types also shows that increased micronutrient concentration affects microbial community composition and functional genes. In addition, structural equation models indicate that micronutrients positively contribute to the ecosystem productivity, both directly (micronutrient availability to plants) and, to a lesser extent, indirectly (via affecting the microbiome). Our findings highlight the importance of micronutrients in explaining soil microbiome structure and ecosystem functioning.

Assessing the Ecotoxicity of Soil Affected by Wildfire

This study was carried out to assess the ecotoxicity of soil affected by wildfire using two laboratory toxicity tests, and to investigate the possibility of application of selected soil amendment into the burnt soil in order to improve its properties for faster post-fire reclamation. A phytotoxicity test is a fast-indicative test for revealing acute toxicity and was performed on quickly growing plant species Sinapis alba L. and Lepidium sativum L., while a pot experiment is a standardized toxicity test with a longer experiment duration and was carried out with Lolium perenne L., Festuca rubra L., Brassica juncea L. Diatomite, bentonite, compost, and biochar were supplemented to the soil. Regarding the phytotoxicity test only 3% w/w of biochar stimulated the growth of Lepidium sativum L. Pot experiment confirmed that effect of soil application amendments on biomass yield is more significant than the plant species. The average highest biomass yields were achieved in treatments with bentonite and diatomite. Subsequent research should focus on investigating possible combinations of soil amendments for burnt soil reclamation and complementing the experiments with chemical analysis.

Tetracycline stress disturbs the mobilization of protein bodies in seed storage reserves during radicle elongation after seed germination

Residues of antibiotics in the soil can have adverse effects on crop plants related closely to humans. However, there is a lack of knowledge on the phytotoxicity of antibiotics to sensitive species. The aim of our study was mainly to reveal tetracycline stress on the mobilization of seed storage proteins, lipids, and minerals of Chinese cabbage (Brassica rapa L.) during radicle elongation after germination. The Chinese cabbage seed was incubated for 48 h in tetracycline solutions at 1 and 5 μM. For the cotyledons of the seed, the result of TEM showed that tetracycline significantly hindered the mobilization of protein bodies, which was in line with the result of FTIR spectroscopy. However, the mobilization of oil bodies and mineral bodies in cotyledons was not significantly disturbed by the stress of tetracycline, as well as the energy supply in different organs including the cotyledons, hypocotyl, and radicle of the seed. To our knowledge, this is the first study to demonstrate the disturbance on mobilization of protein bodies in seed storage reserves caused by the stress of tetracycline at low levels during radicle elongation after germination.

Aridity and reduced soil micronutrient availability in global drylands

Drylands cover more than 40% of terrestrial surface, and their global extent and socio-ecological importance will increase in the future due to the forecasted increases in aridity driven by climate change. Despite the essential role of metallic micronutrients in life chemistry and ecosystem functioning, it is virtually unknown how their bioavailability changes along aridity gradients at the global scale. Here we analysed soil total and available Cu, Fe, Mn, and Zn in 143 drylands from all continents, except Antarctica, covering a broad range of aridity and soil conditions. We found that total and available micronutrient concentrations in dryland soils were low compared to averages commonly found in soils of natural and agricultural ecosystems globally. Aridity negatively affected the availability of all micronutrients evaluated, mainly indirectly by increasing soil pH and decreasing soil organic matter. Remarkably, the available Fe:Zn ratio decreased exponentially as aridity increased, pointing to stoichiometric alterations. Our findings suggest that increased aridity conditions due to climate change will limit the availability of essential micronutrients for organisms, particularly that of Fe and Zn, which together with other adverse effects (e.g., reduced water availability) may pose serious threats to key ecological processes and services, such as food production, in drylands worldwide.

Multiple factors impact the contents of heavy metals in vegetables in high natural background area of China

A field survey was conducted to investigate the concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd) and lead (Pb) in vegetables, corresponding cultivated soils and irrigation waters from 36 open sites in high natural background area of Wuzhou, South China. Redundancy analysis, Spearman's rho correlation analysis and multiple regression analysis were adopted to evaluate the contributions of impacting factors on metal contents in the edible parts of vegetables. This study concluded that leafy and root vegetables had relatively higher metal concentrations and adjusted transfer factor values compared to fruiting vegetables according to nonparametric tests. Plant species, total soil metal content and soil pH value were affirmed as three critical factors with the highest contribution rate among all the influencing factors. The bivariate curve equation models for heavy metals in the edible vegetable tissues were well fitted to predict the metal concentrations in vegetables. The results from this case study also suggested that it could be one of efficient strategies for clean agricultural production and food safety in high natural background area to breed vegetable varieties with low heavy metal accumulation and to enlarge planting scale of these varieties.

Impact of vineyard abandonment and natural recolonization on metal content and availability in Mediterranean soils

Abandonment of vineyards after uprooting has dramatically increased in last decades in Mediterranean countries, often followed by vegetation expansion processes. Inadequate management strategies can have negative consequences on soil quality. We studied how the age and type of vegetation cover and several environmental characteristics (lithology, soil properties, vineyard slope and so on) after vineyard uprooting and abandonment contribute to the variation patterns in total, HAc (acetic acid-method, HAc) and EDTA-extractable (ethylenediaminetetraacetic acid-method) concentrations of Cd, Cu, Pb and Zn in soils. We sampled 141 points from vineyards and abandoned vineyard Mediterranean soils recolonized by natural vegetation in recent decades. The contribution of several environmental variables (e.g. age and type of vegetation cover, lithology, soil properties and vineyard slope) to the total and extractable concentrations of metals was evaluated by canonical ordination based on redundancy analysis, considering the interaction between both environmental and response variables. The ranges of total metal contents were: 0.01-0.15 (Cd), 2.6-34 (Cu), 6.6-30 (Pb), and 29-92mgkg(-1) (Zn). Cadmium (11-100%) had the highest relative extractability with both extractants, and Zn and Pb the lowest. The total and EDTA-extractable of Cd, Pb and Zn were positively related to the age of abandonment, to the presence of Agrostis castellana and Retama sphaerocarpa, and to the contents of Fe-oxides, clay and organic matter (OM). A different pattern was noted for Cu, positively related to vineyard soils. Soil properties successfully explained HAc-extractable Cd, Cu, Pb and Zn but the age and type of vegetation cover lost significance. Clay content was negatively related to HAc-extractable Cu and Pb; and OM was positively related to HAc-Cd and Zn. In conclusion, the time elapsed after vineyard uprooting, and subsequent land abandonment, affects the soil content and availability of metals, and this impact depended on the colonizing plant species and soil properties.