The MdmiR156n Regulates Drought Tolerance and Flavonoid Synthesis in Apple Calli and Arabidopsis.

Drought is the major abiotic stress that limits apple productivity and quality. To date, many important and divergent regulatory functions of miR156/SBP genes in plant growth and development have been well understood. However, little is known about the role of apple miR156 in response to abiotic stress. To better understand the functions of MdmiR156 in abiotic stress tolerance, we constructed the overexpression (OE) and short tandem target mimic (STTM) vector of MdmiR156n and performed its functional analysis through the characterization of transgenic apple calli and Arabidopsis thaliana plants. In this study, MdmiR156n overexpression significantly increased the length of primary roots and the number of lateral roots in transgenic Arabidopsis plants under drought stress. In addition, MdmiR156n transgenic Arabidopsis and apple calli had a lower electrolyte leakage rate and less cell membrane damage than WT and STTM156 after drought stress. Further studies showed that MdmiR156n overexpression promoted the accumulation of flavonoids and scavenging of reactive oxygen species (ROS) under drought conditions in transgenic apple calli and A. thaliana plants. Taken together, overexpression MdmiR156n enhances drought tolerance by regulating flavonoid synthesis and ROS signaling cascades in apple calli and A. thaliana.

Ethylene increases the cold tolerance of apple via the MdERF1B-MdCIbHLH1 regulatory module.

Cold stress has always been a major abiotic factor affecting the yield and quality of temperate fruit crops. Ethylene plays a critical regulatory role in the cold stress response, but the underlying molecular mechanisms remain elusive. Here, we revealed that ethylene positively modulates apple responses to cold stress. Treatment with 1-aminocyclopropane-1-carboxylate (an ethylene precursor) and aminoethoxyvinylglycine (an ethylene biosynthesis inhibitor) respectively increased and decreased the cold tolerance of apple seedlings. Consistent with the positive effects of ethylene on cold stress responses, a low-temperature treatment rapidly induced ethylene release and the expression of MdERF1B, which encodes an ethylene signaling activator, in apple seedlings. Overexpression of MdERF1B significantly increased the cold tolerance of apple plant materials (seedlings and calli) and Arabidopsis thaliana seedlings. A quantitative real-time PCR analysis indicated that MdERF1B upregulates the expression of the cold-responsive gene MdCBF1 in apple seedlings. Moreover, MdCIbHLH1, which functions upstream of CBF-dependent pathways, enhanced the binding of MdERF1B to target gene promoters as well as the consequent transcriptional activation. The stability of MdERF1B-MdCIbHLH1 was affected by cold stress and ethylene. Furthermore, MdERF1B interacted with the promoters of two genes critical for ethylene biosynthesis, MdACO1 and MdERF3. The resulting upregulated expression of these genes promoted ethylene production. However, the downregulated MdCIbHLH1 expression in MdERF1B-overexpressing apple calli significantly inhibited ethylene production. These findings imply that MdERF1B-MdCIbHLH1 is a potential regulatory module that integrates the cold and ethylene signaling pathways in apple.

MdMKK9-Mediated the Regulation of Anthocyanin Synthesis in Red-Fleshed Apple in Response to Different Nitrogen Signals.

The mitogen-activated protein kinase (MAPK) signaling cascade is a widely existing signal transduction system in eukaryotes, and plays an important role in the signal transduction processes of plant cells in response to environmental stress. In this study, we screened MdMKK9, a gene in the MAPK family. This gene is directly related to changes in anthocyanin synthesis in the 'Daihong' variety of red-fleshed apple (Malus sieversii f neidzwetzkyana (Dieck) Langenf). MdMKK9 expression was up-regulated in 'Daihong' tissue culture seedlings cultured at low levels of nitrogen. This change in gene expression up-regulated the expression of genes related to anthocyanin synthesis and nitrogen transport, thus promoting anthocyanin synthesis and causing the tissue culture seedlings to appear red in color. To elucidate the function of MdMKK9, we used the CRISPR/Cas9 system to construct a gene editing vector for MdMKK9 and successfully introduced it into the calli of the 'Orin' apple. The MdMKK9 deletion mutants (MUT) calli could not respond to the low level of nitrogen signal, the expression level of anthocyanin synthesis-related genes was down-regulated, and the anthocyanin content was lower than that of the wild type (WT). In contrast, the MdMKK9-overexpressed calli up-regulated the expression level of anthocyanin synthesis-related genes and increased anthocyanin content, and appeared red in conditions of low level of nitrogen or nitrogen deficiency. These results show that MdMKK9 plays a role in the adaptation of red-fleshed apple to low levels of nitrogen by regulating the nitrogen status and anthocyanin accumulation.

HEAT SHOCK FACTOR A8a Modulates Flavonoid Synthesis and Drought Tolerance.

Drought is an important environmental factor affecting the growth and production of agricultural crops and fruits worldwide, including apple (Malus domestica). Heat shock factors (HSFs) have well-documented functions in stress responses, but their roles in flavonoid synthesis and the flavonoid-mediated drought response mechanism remain elusive. In this study, we demonstrated that a drought-responsive HSF, designated MdHSFA8a, promotes the accumulation of flavonoids, scavenging of reactive oxygen species, and plant survival under drought conditions. A chaperone, HEAT SHOCK PROTEIN90 (HSP90), interacted with MdHSFA8a to inhibit its binding activity and transcriptional activation. However, under drought stress, the MdHSP90-MdHSFA8a complex dissociated and the released MdHSFA8a further interacted with the APETALA2/ETHYLENE RESPONSIVE FACTOR family transcription factor RELATED TO AP2.12 to activate downstream gene activity. In addition, we demonstrated that MdHSFA8a participates in abscisic acid-induced stomatal closure and promotes the expression of abscisic acid signaling-related genes. Collectively, these findings provide insight into the mechanism by which stress-inducible MdHSFA8a modulates flavonoid synthesis to regulate drought tolerance.

Methylation of MdMYB1 locus mediated by RdDM pathway regulates anthocyanin biosynthesis in apple.

Methylation at the MdMYB1 promoter in apple sports has been reported as a regulator of the anthocyanin pathway, but little is known about how the locus is recognized by the methylation machinery to regulate anthocyanin accumulation. In this study, we analysed three differently coloured 'Fuji' apples and found that differences in the transcript levels of MdMYB1, which encodes a key regulator of anthocyanin biosynthesis, control the anthocyanin content (and therefore colour) in fruit skin. The CHH methylation levels in the MR3 region (-1246 to -780) of the MdMYB1 promoter were found to be negatively correlated with MdMYB1 expression. Thus, they were ideal materials to study DNA methylation in apple sports. The protein of RNA-directed DNA methylation (RdDM) pathway responsible for CHH methylation, MdAGO4, was found to interact with the MdMYB1 promoter. MdAGO4s can interact with MdRDM1 and MdDRM2s to form an effector complex, fulfilling CHH methylation. When MdAGO4s and MdDRM2s were overexpressed in apple calli and Arabidopsis mutants, those proteins increase the CHH methylation of AGO4-binding sites. In electrophoretic mobility shift assays, MdAGO4s were found to specifically bind to sequence containing ATATCAGA. Knockdown of MdNRPE1 did not affect the binding of MdAGO4s to the c3 region of the MdMYB1 promoter in 35S::AGO4 calli. Taken together, our data show that the MdMYB1 locus is methylated through binding of MdAGO4s to the MdMYB1 promoter to regulate anthocyanin biosynthesis by the RdDM pathway.

The proanthocyanidin-specific transcription factor MdMYBPA1 initiates anthocyanin synthesis under low-temperature conditions in red-fleshed apples.

In plants, flavonoids play critical roles in resistance to biotic and abiotic stresses, and contribute substantially to the quality, flavor, and nutritional quality of many fruit crops. In apple (Malus × domestica), inbreeding has resulted in severe decreases in the genetic diversity and flavonoid content. Over the last decade, we have focused on the genetic improvement of apple using wild red-fleshed apple resources (Malus sieversii f. niedzwetzkyana). Here, we found that the MYB transcription factors (TFs) involved in the synthesis of proanthocyanidins can be classified into TT2 and PA1 types. We characterized a PA1-type MYB transcription factor, MdMYBPA1, from red-fleshed apple and identified its role in flavonoid biosynthesis using overexpression and knockdown-expression transgenes in apple calli. We explored the relationship between TT2- and PA1-type MYB TFs, and found that MdMYB9/11/12 bind the MdMYBPA1 promoter. In addition, MdMYBPA1 responded to low temperature by redirecting the flavonoid biosynthetic pathway from proanthocyanidin to anthocyanin production. In binding analyses, MdbHLH33 directly bound to the low-temperature-responsive (LTR) cis-element of the MdMYBPA1 promoter and promotes its activity. In addition, the calli expressing both MdMYBPA1 and MdbHLH33, which together form a complex, produced more anthocyanin under low temperature. Our findings shed light on the essential roles of PA1-type TFs in the metabolic network of proanthocyanidin and anthocyanin synthesis in plants. Studies on red-fleshed wild apple are beneficial for breeding new apple varieties with high flavonoid contents.

Methylome and transcriptome analyses of apple fruit somatic mutations reveal the difference of red phenotype.

BACKGROUND: Fruit peel colour is an important agronomic trait for fruit quality. Cytosine methylation plays an important role in gene regulation. Although the DNA methylation level of a single gene is important to affect the phenotype of mutation, there are large unknown of difference of the DNA methylation in plant and its mutants. RESULTS: Using bisulfite sequencing (BS-Seq) and RNA-sequencing (RNA-Seq), we analysed three deep-red-skinned apple (Malus × domestica) mutants (Yanfu 3, YF3; Yanfu 8, YF8; Shannonghong, SNH) and their lighter-skinned parents (Nagafu 2, NF2; Yanfu 3, YF3; Ralls, RL) to explore the different changes in methylation patterns associated with anthocyanin concentrations. We identified 13,405, 13,384, and 10,925 differentially methylated regions (DMRs) and 1987, 956, and 1180 differentially expressed genes (DEGs) in the NF2/YF3, YF3/YF8, and RL/SNH comparisons, respectively. And we found two DMR-associated DEGs involved in the anthocyanin pathway: ANS (MD06G1071600) and F3H (MD05G1074200). These genes exhibited upregulated expression in apple mutants, and differences were observed in the methylation patterns of their promoters. These results suggested that both the regulatory and structural genes may be modified by DNA methylation in the anthocyanin pathway. However, the methylation of structural genes was not the primary reason for expression-level changes. The expression of structural genes may be synergistically regulated by transcription factors and methylation changes. Additionally, the expression of the transcription factor gene MYB114 (MD17G1261100) was upregulated in the deep-red-skinned apple. CONCLUSION: Through the analysis of global methylation and transcription, we did not find the correlation between gene expression and the DNA methylation. However, we observed that the upregulated expression of ANS (MD06G1071600) and F3H (MD05G1074200) in apple mutants results in increased anthocyanin contents. Moreover, MYB114 (MD17G1261100) is likely another regulatory gene involved in apple coloration. Our data provided a new understanding about the differences in formation of apple colour mutants.

MdCOL4 Interaction Mediates Crosstalk Between UV-B and High Temperature to Control Fruit Coloration in Apple.

In many plants, anthocyanin biosynthesis is affected by environmental conditions. Ultraviolet-B (UV-B) radiation promotes anthocyanin accumulation and fruit coloration in apple skin, whereas high temperature suppresses these processes. In this study, we characterized a B-box transcription factor, MdCOL4, from 'Fuji' apple, and identified its role in anthocyanin biosynthesis by overexpressing its encoding gene in apple red callus. The expression of MdCOL4 was reduced by UV-B, but promoted by high temperature. We explored the regulatory relationship between heat shock transcription factors (HSFs) and MdCOL4, and found that MdHSF3b and MdHSF4a directly bound to the heat shock element cis-element of the MdCOL4 promoter. MdCOL4 interacted with MdHY5 to synergistically inhibit the expression of MdMYB1, and MdCOL4 directly bound to the promoters of MdANS and MdUFGT, which encode genes in the anthocyanin biosynthetic pathway, to suppress their expression. Our findings shed light on the molecular mechanism by which MdCOL4 suppresses anthocyanin accumulation in apple skin under UV-B and high temperature.

The B-box zinc finger protein MdBBX20 integrates anthocyanin accumulation in response to ultraviolet radiation and low temperature.

Ultraviolet-B (UV-B) radiation and low temperature promote the accumulation of anthocyanins, which give apple skins their red colour. Although many transcription regulators have been characterized in the UV-B and low-temperature pathways, their interregulation and synergistic effects are not well understood. Here, a B-box transcription factor gene, MdBBX20, was characterized in apple and identified to promote anthocyanin biosynthesis under UV-B conditions in field experiments and when overexpressed in transgenic apple calli. The transcript level of MdBBX20 was significantly induced by UV-B. Specific G-box elements in the promoters of target genes were identified as interaction sites for MdBBX20. Further experimental interrogation of the UV-B signalling pathways showed that MdBBX20 could interact with MdHY5 in vitro and in vivo and that this interaction was required to significantly enhance the promoter activity of MdMYB1. MdBBX20 also responded to low temperature (14°C) with the participation of MdbHLH3, which directly bound a low temperature-response cis elements in the MdBBX20 promoter. These findings demonstrate the molecular mechanism by which MdBBX20 integrates low-temperature- and UV-B-induced anthocyanin accumulation in apple skin.

MYB12 and MYB22 play essential roles in proanthocyanidin and flavonol synthesis in red-fleshed apple (Malus sieversii f. niedzwetzkyana).

Flavonoids are major polyphenol compounds in plant secondary metabolism. Wild red-fleshed apples (Malus sieversii f. niedzwetzkyana) are an excellent resource because of their much high flavonoid content than cultivated apples. In this work, R6R6, R6R1 and R1R1 genotypes were identified in an F1 segregating population of M. sieversii f. niedzwetzkyana. Significant differences in flavonoid composition and content were detected among the three genotypes by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry analysis. Furthermore, two putative flavonoid-related genes encoding R2R3-MYB transcription factors, designated MYB12 and MYB22, were cloned and characterized. The expression patterns of MYB12 and MYB22 directly correlated with those of leucoanthocyanidin reductase and flavonol synthase, respectively. Their roles in flavonoid biosynthesis were identified by overexpression in apple callus and ectopic expression in Arabidopsis. MYB12 expression in the Arabidopsis TT2 mutant complemented its proanthocyanidin-deficient phenotype. Likewise, MYB22 expression in an Arabidopsis triple mutant complemented its flavonol-deficient phenotype. MYB12 could interact with bHLH3 and bHLH33 and played an essential role in proanthocyanidin synthesis. MYB22 was found to activate flavonol pathways by combining directly with the flavonol synthase promoter. Our findings provide a valuable perspective on flavonoid synthesis and provide a basis for breeding elite functional apples with a high flavonoid content.

The ethylene response factor MdERF1B regulates anthocyanin and proanthocyanidin biosynthesis in apple.

KEY MESSAGE: The regulator MdERF1B in the apple (Malus × domestica) ethylene pathway mainly acts on MdMYB9 and MdMYB11 to regulate anthocyanin and proanthocyanidin accumulation. Dietary anthocyanins and proanthocyanidins (PAs) have health benefits for humans, and are associated with decreased risks of coronary heart disease and cancer. Ethylene can enhance reddening of apple (Malus × domestica), but the regulatory mechanism is poorly understood. In this study, an ethylene response factor (ERF), MdERF1B, was identified and functionally characterized. 'Orin' calli overexpressing MdERF1B were generated and then analyzed by quantitative reverse transcription-PCR. Compared with the control calli, the MdERF1B-overexpressing calli showed increased expression levels of MdACO1, MdERF1, and MdERF3 in the ethylene pathway and MdCHS, MdCHI, MdF3H, MdDFR, MdANS, MdLAR, MdANR, MdMYB9 and MdMYB11 in the flavonoid pathway. As a result, the levels of anthocyanins and PAs were significantly increased in the MdERF1B-overexpressing calli. MdERF1B interacted with MdMYB9, MdMYB1, and MdMYB11 proteins in yeast two-hybrid, pull-down, and bimolecular fluorescence complementation assays. Furthermore, in yeast one-hybrid and electrophoretic mobility shift assays, MdERF1B also bound to the promoters of MdMYB9, MdMYB1, and MdMYB11. In a luciferase reporter assay, MdERF1B mainly activated proMdMYB9 and proMdMYB11, promoting their expression levels. This was in agreement with MdERF1B's overexpression in calli, which barely affected MdMYB1 expression. Taken together, our findings provide an insight into the regulatory mechanisms in the ethylene pathway that increase anthocyanin and PA accumulation in apple.

Overexpression of a repressor MdMYB15L negatively regulates anthocyanin and cold tolerance in red-fleshed callus.

The cold-induced metabolic pathway and anthocyanin biosynthesis play important roles in plant growth. In this study, we identified a bHLH binding motif in the MdMYB15L protein using protein sequence analyses. Yeast two-hybrid and pull-down assays showed that MdMYB15L could interact with MdbHLH33. Overexpressing MdMYB15L in red-fleshed callus inhibited the expression of MdCBF2 and resulted in reduced cold tolerance but did not affect anthocyanin levels. Chip-PCR and EMSA analysis showed that MdMYB15L could bind the type II cis-acting element found in the MdCBF2 promoter. Overexpressing MdMYB15L in red-fleshed callus overexpressing MdbHLH33 also reduced cold tolerance and reduced MdbHLH33-induced anthocyanin biosynthesis. Knocking out the bHLH binding sequence of MdMYB15L (LBSMdMYB15L) prevented LBSMdMYB15L from interacting with MdbHLH33. Overexpressing LBSMdMYB15L in red-fleshed callus overexpressing MdbHLH33 also reduced cold tolerance and reduced MdbHLH33-induced anthocyanin biosynthesis. Together, these results suggested that an apple repressor MdMYB15L might play a key role in the cold signaling and anthocyanin metabolic pathways.

The molecular mechanism underlying anthocyanin metabolism in apple using the MdMYB16 and MdbHLH33 genes.

KEY MESSAGE: MdMYB16 forms homodimers and directly inhibits anthocyanin synthesis via its C-terminal EAR repressor. It weakened the inhibitory effect of MdMYB16 on anthocyanin synthesis when overexpressing MdbHLH33 in callus overexpressing MdMYB16. MdMYB16 could interact with MdbHLH33. Anthocyanins are strong antioxidants that play a key role in the prevention of cardiovascular disease, cancer, and diabetes. The germplasm of Malus sieversii f. neidzwetzkyana is important for the study of anthocyanin metabolism. To date, only limited studies have examined the negative regulatory mechanisms underlying anthocyanin synthesis in apple. Here, we analyzed the relationship between anthocyanin levels and MdMYB16 expression in mature Red Crisp 1-5 apple (M. domestica) fruit, generated an evolutionary tree, and identified an EAR suppression sequence and a bHLH binding motif of the MdMYB16 protein using protein sequence analyses. Overexpression of MdMYB16 or MdMYB16 without bHLH binding sequence (LBSMdMYB16) in red-fleshed callus inhibited MdUFGT and MdANS expression and anthocyanin synthesis. However, overexpression of MdMYB16 without the EAR sequence (LESMdMYB16) in red-fleshed callus had no inhibitory effect on anthocyanin. The yeast one-hybrid assay showed that MdMYB16 and LESMdMYB16 interacted the promoters of MdANS and MdUFGT, respectively. Yeast two-hybrid, pull-down, and bimolecular fluorescence complementation assays showed that MdMYB16 formed homodimers and interacted with MdbHLH33, however, the LBSMdMYB16 could not interact with MdbHLH33. We overexpressed MdbHLH33 in callus overexpressing MdMYB16 and found that it weakened the inhibitory effect of MdMYB16 on anthocyanin synthesis. Together, these results suggested that MdMYB16 and MdbHLH33 may be important part of the regulatory network controlling the anthocyanin biosynthetic pathway.

Hypermethylation in the promoter regions of flavonoid pathway genes is associated with skin color fading during 'Daihong' apple fruit development.

Apple fruit skin color fading is not well understood although the molecular mechanism of skin color formation is well known. The red-fleshed apple cultivar 'Daihong' (DH) exhibited fading skin color during fruit development despite having a heterozygous R6 allele but lacking Red-TE for red fruit skin. In this study, transcriptomic analysis revealed the expression level of MdMYB10 increased with fruit development whereas reduced expression levels of MdMYBPA1, MdCHS, MdANS, MdUFGT, MdLAR, and MdANR were observed, consistent with decreased levels of chalcone, anthocyanin, catechin, epicatechin, and procyanidin B2. Whole-genome bisulfite sequencing (WGBS) indicated a global gain in cytosine methylation levels and increased methylation in 5' and 3' flanking regions of genes and transposable elements (TEs), and in TE bodies in all CG, CHG and CHH contexts, especially the mCHH context, during fruit development. The increased DNA methylation was attributed to reduced expression levels of DNA demethylase genes, including MdDME1, MdROS1, and MdROS2. Association analysis revealed a significant negative correlation between promoter methylation levels of MdCHS, MdCHI, MdMYBPA1, and their respective transcript levels, as well as a negative correlation between promoter methylation levels of MdCHS, MdCHI, MdANR, and MdFLS, and the content of chalcones, naringenin-7-glucoside, epicatechin, and quercetin. Treatment with the DNA demethylation agent 5-aza-2'-deoxycytidine verified the negative correlation between DNA methylation and gene expression within the flavonoid pathway. These findings suggest that hypermethylation in promoter regions of genes of the flavonoid biosynthesis pathway is associated with the reduction of gene expression and flavonoid content, and fruit skin color fading during DH apple development.

A Functional InDel in the WRKY10 Promoter Controls the Degree of Flesh Red Pigmentation in Apple.

MYB transcription factors have been linked to anthocyanin synthesis and various color phenotypes in plants. In apple, MYB10 confers a red-flesh phenotype due to a minisatellite insertion in its R6 promoter, but R6:MYB10 genotypes exhibit various degrees of red pigmentation in the flesh, suggesting the involvement of other genetic factors. Here, it is shown that MdWRKY10, a transcription factor identified via DNA pull-down trapping, binds to the promoter of MdMYB10 and activates its transcription. MdWRKY10 specifically interacts with the WDR protein MdTTG1 to join the apple MYB-bHLH-WDR (MBW) complex, which significantly enhances its transcriptional activation activity. A 163-bp InDel detected in the promoter region of the alleles of MdWRKY10 in a hybrid population of identical heterozygous genotypes regarding R6 by structural variation analysis, contains a typical W-box element that MdWRKY10 binds to for transactivation. This leads to increased transcript levels of MdWRKY10 and MdMYB10 and enhanced anthocyanin synthesis in the flesh, largely accounting for the various degrees of flesh red pigmentation in the R6 background. These findings reveal a novel regulatory role of the WRKY-containing protein complex in the formation of red flesh apple phenotypes and provide broader insights into the molecular mechanism governing anthocyanin synthesis in plants.

Mapping and spatiotemporal dynamics of land-use and land-cover change based on the Google Earth Engine cloud platform from Landsat imagery: A case study of Zhoushan Island, China.

Land resources are an essential foundation for socioeconomic development. Island land resources are limited, the type changes are particularly frequent, and the environment is fragile. Therefore, large-scale, long-term, and high-accuracy land-use classification and spatiotemporal characteristic analysis are of great significance for the sustainable development of islands. Based on the advantages of remote sensing indices and principal component analysis in accurate classification, and taking Zhoushan Archipelago, China, as the study area, in this work long-term satellite remote sensing data were used to perform land-use classification and spatiotemporal characteristic analysis. The classification results showed that the land-use types could be exactly classified, with the overall accuracy and Kappa coefficient greater than 94% and 0.93, respectively. The results of the spatiotemporal characteristic analysis showed that the built-up land and forest land areas increased by 90.00 km2 and 36.83 km2, respectively, while the area of the cropland/grassland decreased by 69.77 km2. The areas of the water bodies, tidal flats, and bare land exhibited slight change trends. The spatial coverage of Zhoushan Island continuously expanded toward the coast, encroaching on nearby sea areas and tidal flats. The cropland/grassland was the most transferred-out area, at up to 108.94 km2, and built-up land was the most transferred-in areas, at up to 73.31 km2. This study provides a data basis and technical support for the scientific management of land resources.

Geochemical characteristics of heavy metals in surface sediments of the Bohai Strait, China.

The heavy metal (Cr, Cu, Ni, Pb, and Zn) content and particle size of surface sediment samples taken from 123 sites in the Bohai Strait of China were analyzed. All five heavy metals showed a similar distribution in the Bohai Strait, with lower concentrations in the middle and higher concentrations at the sides of the strait. The amount of heavy metals was lowest in the Laotieshan Channel due to the rapid current in this channel. According to our calculated values of the pollution index (Pi), only 1.6 % of the sample sites were polluted by Cr and Cu. The calculated geo-accumulation index (Igeo) values showed that few of the sites were polluted by heavy metals. The level of Pb was controlled by both terrigenous inputs and clay adsorption, while the levels of the other heavy metals (Cr, Cu, Ni, and Zn) were mainly controlled by terrigenous inputs.

Distribution, source, and contamination assessment of heavy metals in surface sediments of the Zhifu Bay in northern China.

In this study, 30 surface sediment samples were collected from Zhifu Bay in northern China and analyzed for heavy metals; in addition, their concentrations and pollution status were evaluated. The distributions of Cu and Zn were similar and mainly dominated by fine-grained sediments, whereas the other heavy metal distributions were not very regular. Al was positively correlated with Cu and Zn, and weakly correlated with Pb, As, and Hg. Except for some stations that showed minor enrichment and were unpolluted to moderately polluted by Cr, Cd, and Hg, the overall quality of sediments in the study area was good. Three principal components with eigenvalues >1 were estimated, accounting for 72.06 % of the total variability and representing natural sources, natural and anthropogenic, and anthropogenic sources, respectively.

Distribution and pollution assessment of heavy metals in surface sediments along the Weihai coast, China.

In this study, 78 surface sediment samples were collected from the Weihai coastal area and analyzed for heavy metals. Their concentrations and pollution status were evaluated. The distribution of heavy metals was mainly dominated by sediment grain size, and the sediments in the Weihai, Sanggou, and Rushan Bays, which have finer grain sizes, had higher concentrations. The mean geoaccumulation index values for all heavy metals were <0. Expect for Hg, the mean enrichment factor values of the other metals were <1.5, indicating that they are natural sourced. Overall, the environmental quality of the Weihai costal area was relatively good and should be maintained and protected. The heavy metals that had potential impacts on the ecological environment were Cd and Hg, which were mainly distributed west of Weihai Bay and inside Rushan Bay. They are affected by human activities and must be controlled.

Heavy metal concentration profiles and pollution assessment in the Jiangsu offshore area, China.

The concentration profiles of various major and trace heavy metals (Cu, Pb, Zn, Cr, Cd, As, Hg, Ni, Li, and Co) were investigated along a 40.1-m-long sediment core in the offshore Jiangsu area of China, to assess their depositional trends and contamination levels. All metals, except Cd, exhibited similar profiles with high average concentrations during the Marine Isotope Stage 2-4 period. The sediment trace-metal concentrations were primarily related to grain size and sediment sources, with almost all heavy metals (except Cd) being positively correlated. Enrichment factors, geoaccumulation indices, and principal component analysis indicated no elemental enrichment or contamination. The high EF and Igeo values of As, Hg, and Li may be related to their background values.