Novel insights into antimony mobilization in different high- antimony aquifers from the molecular signatures of dissolved organic matter.

The crucial role of the fluorescent components of dissolved organic matter (DOM) in controlling antimony (Sb) mobilization in groundwater has been confirmed. However, the molecular signatures contributing to Sb enrichment in DOM remain unknown. This study aims to investigate the origins and molecular compositions of DOM in different high-Sb aquifers (Sb-mining and no-Sb-mining aquifer), as well as compare different molecular signatures of DOM and mechanisms for Sb migration. The findings showed that Sb concentrations in Sb-mining aquifer exhibited a positive correlation with lignin- and tannin-like molecules characterized by high O/C and low H/C ratios, indicating an increased abundance of aromatic components with higher Humification Index and SUV-absorbance at 254 nm, compared to no-Sb-mining aquifer. Correspondingly, the complexation and competitive adsorption were considered as the predominate formation mechanisms on Sb enrichment in Sb-mining aquifer. In addition, high abundances of bioreactivity DOM may facilitated the migration of Sb via electron transfer and competitive adsorption in native no-Sb-mining aquifer. The outcomes of this investigation offer novel insights into the mechanism on Sb enrichment influenced by DOM at the molecule level.

Fine mapping and cloning of a novel BrSCC1 gene for seed coat color in Brassica rapa L.

KEY MESSAGE: A novel BrSCC1 gene for seed coat color was fine mapped within a 41.1-kb interval on chromosome A03 in Brassica rapa and functionally validated by ectopic expression analysis. Yellow seed is a valuable breeding trait that can be potentiality applied for improving seed quality and oil productivity in oilseed Brassica crops. However, only few genes for yellow seed have been identified in B. rapa. We previously identified a minor quantitative trait locus (QTL), qSC3.1, for seed coat color on chromosome A03 in B. rapa. In order to isolate the seed coat color gene, a brown-seeded chromosome segment substitution line, CSSL-38, harboring the qSC3.1, was selected and crossed with the yellow-seeded recurrent parent, a rapid cycling inbred line of B. rapa (RcBr), to construct the secondary F2 population. Metabolite identification suggested that seed coat coloration in CSSL-38 was independent of proanthocyanidins (PAs) accumulation. Genetic analysis revealed that yellow seed was controlled by a single recessive gene, Seed Coat Color 1 (BrSCC1). Utilizing bulked segregant analysis (BSA)-seq and secondary F2 and F2:3 recombinants analysis, BrSCC1 was fine mapped within a 41.1-kb interval. By integrating gene expression profiling, genome sequence comparison, metabolite analysis, and functional validation through ectopic expression in Arabidopsis, the BraA03g040800.3C gene was confirmed to be BrSCC1, which positively correlated with the seed coat coloration. Our study provides a novel gene resource for the genetic improvement of yellow seeds in oilseed B. rapa.

Geochemical impact of dissolved organic matter on antimony mobilization in shallow groundwater of the Xikuangshan antimony mine, Hunan Province, China.

Dissolved organic matter (DOM) is widely used in aquatic systems to control the environmental fate of As. However, similar to the behavior of As, Sb mobilization driven by DOM is poorly understood. A total of 25 samples were collected from shallow groundwater in the Xikuangshan mine to compare the spectroscopic characteristics and chemical properties of DOM between high- and low-Sb groundwater and to determine the roles of DOM in Sb mobility. The concentrations of Sb and DOM varied from 0.003 to 18.402 mg/L (mean: 3.407 mg/L) and 0.38 to 9.90 mg/L (mean: 2.49 mg/L), respectively. The DOM of the D3x4 water was primarily dominated by terrestrial and microbial humic-like and fulvic acid substances, with a relatively small contribution of tryptophan-like components. Complexing agents, competitive adsorption, and photopromoted oxidation under sunlight were considered as the formation mechanisms for DOM-controlled Sb(V)-dominated Sb species in D3x4 water. The weakly alkaline and oxidizing conditions, and the presence of Fe hydroxides facilitated the promotion of Sb(V) concentration. The findings of this study further enhance our understanding of the Sb migration mechanism in oxic groundwater.

Fine mapping and analysis of candidate genes for qFT7.1, a major quantitative trait locus controlling flowering time in Brassica rapa L.

KEY MESSAGE: qFT7.1, a major QTL for flowering time in Brassica rapa was fine-mapped to chromosome A07 in a 56.4-kb interval, in which the most likely candidate gene is BraA07g018240.3C. In Brassica rapa, flowering time (FT) is an important agronomic trait that affects the yield, quality, and adaption. FT is a complicated trait that is regulated by many genes and is affected greatly by the environment. In this study, a chromosome segment substitution line (CSSL), CSSL16, was selected that showed later flowering than the recurrent parent, a rapid-cycling inbred line of B. rapa (RcBr). Using Bulked Segregant RNA sequencing, we identified a late flowering quantitative trait locus (QTL), designated as qFT7.1, on chromosome A07, based on a secondary-F2 population derived from the cross between CSSL16 and RcBr. qFT7.1 was further validated by conventional QTL mapping. This QTL explained 39.9% (logarithm of odds = 32.2) of the phenotypic variations and was fine mapped to a 56.4-kb interval using recombinant analysis. Expression analysis suggested that BraA07g018240.3C, which is homologous to ATC (encoding Arabidopsis thaliana CENTRORADIALIS homologue), a gene for delayed flowering in Arabidopsis, as the most promising candidate gene. Sequence analysis demonstrated that two synonymous mutations existed in the coding region and numerous bases replacements existed in promoter region between BraA07g018240.3C from CSSL16 and RcBr. The results will increase our knowledge related to the molecular mechanism of late flowering in B. rapa and lays a solid foundation for the breeding of late bolting B. rapa.

Increase in fluoride concentration in mine water in Shendong mining area, Northwest China: Insights from isotopic and geochemical signatures.

Mine water poses severe threats to the quality of the water supply and ecological environment of the Shendong mining areas owing to its excessive fluoride (F-) content. However, the geochemical behaviours and enrichment mechanisms responsible for F⁻ enrichment during mining activities are not fully understood. In total, 18 Yanan groundwater and 45 mine water samples were collected to analyse the spatial distribution, hydrogeochemical behaviours, and formation mechanisms related to elevated F- levels by analysing the stable isotopes and water-rock interactions. In this study, F- concentrations in mine water samples varied from 0.16 to 12.75 mg/L, with a mean value of 6.10 mg/L, and 77.78% of the mine water samples had a concentration that exceeded China's national standards (1.00 mg/L) for drinking water. The F- concentration was markedly high in the mine water samples, with the mean F- concentration being 1.58 times of that in the Yanan groundwater samples. The results of stable isotopes (18OH2O, D, 34SSO4, and 18OSO4) and water-rock interaction analyses suggested that cation exchange and competitive effects were the dominant factors responsible for elevated F- concentration in mine water during mining activities. Thus, the weathering of F-bearing minerals, agriculture, and domestic activities do not play a significant role in the secondary enrichment of F- concentration.

Spatial distribution, geochemical behaviors and risk assessment of antimony in rivers around the antimony mine of Xikuangshan, Hunan Province, China.

Pollutants derived from antimony (Sb) mining can easily cause pollution of surrounding water bodies. However, qualitative source analysis of river pollution is mostly conducted, and quantitative source analysis is still lacking. A total of 21 water samples were collected to analyze the pollution status of the heavy metal element Sb, explore the Xikuangshan (XKS) area river heavy metals pollution mechanism, undertake quantitative analysis of the sources of pollution, and carry out irrigation water suitability assessment and potential ecological risk assessment. The results showed that, compared with the mining non-affected area, the maximum excess multiple of Sb in surface water and rivers in Hunan XKS area is 411.31. When the river fluid flows through the mining-affected area, the heavy metal element Sb content increases rapidly, and then decreases due to dilution process. Positive matrix factorization (PMF) source analysis showed that the main source of Sb pollution in the rivers is the impact of mining and smelting (83.60%), followed by the role of waste rock leaching (16.40%). After irrigation, 27.78% of the river water had strong ecological risks, and 16.67% had extremely strong ecological risks. This achievement provides a theoretical basis and technical guarantee for protecting and using the local water body of the mining area.

Environmental behaviors of PAHs in Ordovician limestone water of Fengfeng coal mining area in China.

In this study, we collected a total of 15 Ordovician limestone (OL) water, 4 shallow groundwater, 3 mine water, 2 surface water, and 2 coal bedrock water samples, aiming to analyze the characteristics of distributions and sources of polycyclic aromatic hydrocarbons (PAHs) in OL water in a typical exploited coal mine named as Fengfeng mining area. Firstly, the PAHs behaviors and characteristics in different types of water of the mining area were investigated and summarized. And then, the hydrogen and oxygen isotopes were combined with isomer ratio method to determine the characteristics, sources, and behaviors of PAHs in OL water, respectively. Results showed that the concentration of PAHs ranged from 0.06 to 0.56 ng/L in OL water of Fengfeng Mine. Among them, the dominant 2-4 cyclic PAHs, including Nap, Phe, Flt, and Flu, were detected at a low concentration level with high detection rate. Characteristic compound ratios Ant/(Ant + Phe) and Flt/(Flt + Pyr) showed that the PAHs were derived from the combustion of the coal and biomass. The results of δD/δ18O and δD/Phe testing showed that the PAHs in most OL water came from rainfall infiltration recharge with coal and biomass combustion products in exposed bedrock area at high altitude. The PAHs of some polluted areas were derived from leakage recharge of shallow groundwater, mine water, and coal bedrock water.