Effects of soil properties on heavy metal bioavailability and accumulation in crop grains under different farmland use patterns.

Mining activities have increased the accumulation of heavy metals in farmland soil and in food crops. To identify the key soil properties influencing heavy metal bioavailability and accumulation in food crops, 81 crop samples and 81 corresponding agricultural soil samples were collected from rape, wheat, and paddy fields. Heavy metal (copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), iron (Fe), and manganese (Mn)) concentrations in soils and rape, wheat, rice grains were determined using inductively coupled plasma atomic emission spectroscopy, and soil physicochemical properties (pH, organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium (AK)) were analyzed. Soil extractable metals were extracted using various single extractants (DTPA, EDTA, NH4OAc, NH4NO3, and HCl). The average concentrations of Cu, Zn, Pb, Cd, and Mn in the soil samples all exceeded the local geochemical background value (background values of Cu, Zn, Pb, Cd, and Mn are 43.0, 81.0, 28.5, 0.196, and 616 mg/kg, respectively), and Cd over-standard rate was the highest, at 98%. Furthermore, soil total Cd concentrations (0.1-24.8 mg/kg) of more than 86% of the samples exceeded the soil pollution risk screening value (GB 15618-2018). The sources of Cu, Zn, Pb, Cd, and Mn in soils were mainly associated with mining activities. The key factors influencing heavy metal bioavailability were associated with the types of extractants (complexing agents or neutral salt extractants) and the metals. Cd and Pb concentrations in most wheat and rice grain samples exceeded the maximum allowable Cd and Pb levels in food, respectively, and Cd concentrations in approximately 10% of the rice grain samples exceeded 1.0 mg/kg. Furthermore, rice and wheat grains exhibited higher Cd accumulation capacity than rape grains, and despite the high soil Cd concentrations in the rape fields, the rape grains were safe for consumption. High soil pH and AK restricted Cd and Cu accumulation in wheat grains, respectively. Soil properties seemed to influence heavy metal accumulation in rice grains the most.

Comparison and interpretation of characteristics of Rhizosphere microbiomes of three blueberry varieties.

BACKGROUND: Studies on the rhizosphere microbiome of various plants proved that rhizosphere microbiota carries out various vital functions and can regulate the growth and improve the yield of plants. However, the rhizosphere microbiome of commercial blueberry was only reported by a few studies and remains elusive. Comparison and interpretation of the characteristics of the rhizosphere microbiome of blueberry are critical important to maintain its health. RESULTS: In this study, a total of 20 rhizosphere soil samples, including 15 rhizosphere soil samples from three different blueberry varieties and five bulk soil samples, were sequenced with a high-throughput sequencing strategy. Based on these sequencing datasets, we profiled the taxonomical, functional, and phenotypic compositions of rhizosphere microbial communities for three different blueberry varieties and compared our results with a previous study focused on the rhizosphere microbiome of blueberry varieties. Our results demonstrated significant differences in alpha diversity and beta diversity of rhizosphere microbial communities of different blueberry varieties and bulk soil. The distribution patterns of taxonomical, functional, and phenotypic compositions of rhizosphere microbiome differ across the blueberry varieties. The rhizosphere microbial communities of three different blueberry varieties could be distinctly separated, and 28 discriminative biomarkers were selected to distinguish these three blueberry varieties. Core rhizosphere microbiota for blueberry was identified, and it contained 201 OTUs, which were mainly affiliated with Proteobacteria, Actinobacteria, and Acidobacteria. Moreover, the interactions between OTUs of blueberry rhizosphere microbial communities were explored by a co-occurrence network of OTUs from an ecological perspective. CONCLUSIONS: This pilot study explored the characteristics of blueberry's rhizosphere microbial community, such as the beneficial microorganisms and core microbiome, and provided an integrative perspective on blueberry's rhizosphere microbiome, which beneficial to blueberry health and production.

Interactions between heavy metals and other mineral elements from soil to medicinal plant Fengdan (Paeonia ostii) in a copper mining area, China.

In order to analyze the interaction relationship between heavy metals and other mineral elements during the processes of absorption and translocation by plant grown on heavy metal-contaminated area, the concentrations of Cu, Zn, Mn, Cd, Pb, Ca, Mg, Fe, and K in the medicinal plant Paeonia ostii T. Hong et J. X. Zhang and its rhizospheric soil were determined, which grow around an abandoned copper tailings reservoir in Tongling City, China. Geo-accumulation index (Igeo) calculation indicated that Cu and Pb are the main pollution elements in the rhizospheric soil. Moreover, the Cu and Pb concentrations in the cortex moutan of P. ostii exceeded the maximum permissible limits for food product safety. The bioaccumulation factor values of the tested metals in plant roots were found < 0.50, with the exception of Ca (maximum 5.99). The translocation factor values of detected heavy metals Cd and Pb were more than 1.00, which indicated that P. ostii could be considered a potential accumulator plant for Cd and Pb. Significant positive correlations including Cu-Cd, Cu-Zn, Cu-Pb, Cd-Zn, Cd-Fe, Cd-Fe, Zn-Pb, Pb-Fe, Mn-Fe, and Ca-Mg in the cortex moutan and Cu-Zn, Cu-Fe, Zn-Mg, Zn-Fe, and Mn-K in the leaves were observed (P < 0.05). Significant positive correlation between Cu, Zn, Mg, and Fe was also confirmed in the processes of absorption and translocation from the soil to plant (P < 0.05), which evidenced that synergistic element interactions of the essential elements Cu, Zn, Mg, and Fe are a result of the similarity in their ionic radii and octahedral coordination geometry.

Ecological and health risks of heavy metal on farmland soils of mining areas around Tongling City, Anhui, China.

To investigate and assess heavy metal contamination on the farmland soils of a typical mining city, the concentrations of Cu, Cd, Zn, Pb, As, and Cr were analyzed from four mining areas (Tongguan District (TGD), Shunan Town (SAT), Tianmen Town (TMT), and Zhongmin Town (ZMT)) and two control areas (Xilian Township (XLT), Donglian Township (DLT)) in Tongling City, China. The total metal concentrations in the soils were in the following order: Cd ˂ As ≤ Pb ˂ Cu ˂ Cr ≤ Zn. Total metal concentrations in the soils of mining areas were significantly higher than those of the control areas (P < 0.05). According to the Chinese Environmental Quality Standard for Soils (GB 15618-1995) and geo-accumulation index (Igeo), Cd and As pollution in the farmland soils of the mining areas was the most severe, followed by Cu. The Igeo values of soil heavy metals of TGD and SAT were the most highest, followed by those of TMT and ZMT. The health risk quotient (HQ) of heavy metals in the soils showed as follows: HQAs ˃ HQPb ˃ HQCr ˃ HQCd ˃ HQCu ˃ HQZn, and the total average daily exposed dose (non-carcinogenic risk) of As was the highest except that of Cd. The contribution rate of carcinogenic risk index (CR) to total carcinogenic risk index (TCR) of As and Cd in the topsoil for adults was 99.91% and 0.09% respectively, and the value for children was 99.87% and 0.13%. The CR and TCR of As in the farmland of mining areas were greater than 10-4, which showed the carcinogenic risk is an intolerable range for both adults and children. According to the results of the present study, it can help the local people know the pollution of heavy metals in farmland and adopt the best suitable agriculture practices.

[Enzyme activities in Paeonia ostii rhizosphere and non-rhizosphere soil of Tongling copper mining].

The study on the calatase, polyphenol-oxidase, invertase, urease and phosphatase activities in Paeonia ostii rhizosphere and non-rhizosphere soil of Tongling copper mining showed that all test enzyme activities were higher in rhizosphere than in non-rhizosphere soil. Soil calatase, urease and phosphatase were sensitive to heavy metals pollution, and their activities could be used as the indicators of heavy metals' joint pollution. The effects of rhizosphere environment on the soil enzyme activities were in the sequence of phosphatase > urease > calatase > invertase > polyphenol-oxidase, and the affecting rate was 131.562%, 92.492%, 87.557%, 59.673% and 34.076%, respectively. The test enzyme activities were negatively correlated with soil heavy metals pollution, and the correlation coefficients were all higher than -0.898, suggesting the inhibitory effects of heavy metals' joint pollution on soil enzyme activities. P. ostii could effectively improve soil environment, and thus, enhance the activities of soil enzymes.

[Heavy metals pollution of Paeonia ostii land at copper-tailings reservoir of Tongling city: a preliminary study].

The study on the soil and Paeonia ostii Cu, Cd, Pb and Zn at the copper-tailings reservoir of Tongling City, Anhui Province showed that the forms and contents of test heavy metals were differed in Paeonia ostii-planted and control soils. The Cu and Cd contents in control soil were 4.36-14.43 and 3.67-3.86 times of the 2nd national standard for soil environmental quality, respectively, and the composite pollution index of the heavy metals in Paeonia ostii-planted soil was up to 5.607. The heavy metals content in Paeonia ostii leaf and root-stem was in order of Cu>Zn>Pb>Cd, and that in Paeonia ostii stem and root- peel was Zn>Cu>Pb>Cd. The comparison of the heavy metals contents in Paeonia ostii with the criterion about herbal medicine showed that the Cu content in Paeonia ostii was 1.43-2.53 times of the criterion, and the Cd content was 1.17-3.17 times of the criterion.

[Chemical forms of heavy metals in the soils and plants of copper tailings yard].

The study on the chemical forms of heavy metals in the soils and plants at the copper tailings yard in Tongling City indicated that the soils were extremely poor, with organic mater content being 2.6-5.8 g x kg(-1), only 1/15 of the control, while their Cu, Cd, Pb and Zn contents were higher than the control, with Cu 809.30-1395.54 mg x kg(-1) and Cd 3.25-6.35 mg x kg(-1), as 30-60 times as those of the control. The heavy metals contents in Zoysia japonica and Trifolium pratense had a significantly positive correlation with the contents of their exchangeable and organic forms in soils, a significantly or very significantly negative correlation with the forms of Fe-Mn oxides and carbonate, and no correlation with residual form. The main forms of Cu, Zn and Pb in Z. japonica and T. pratense were HAC-and HCl-extractable, and residual. The NaCl-extractable Zn content in the roots, stems and leaves of Z. japonica and T. pratense occupied a higher proportion, while NaCl-extractable Cd was the main form of Cd in both of the plants, not only in their roots but also in their leaves.