Aug 2021, Volume 3 Issue 3

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  • Rice assembles microbial populations in rhizosphere from surrounding soils to promote plant growth under waterlogged anaerobic condition, but the spatio-temporal dynamics of microbiota in response to pesticide pollution might impact the resilience of rice grown in polluted soils. Taking a typical organochlorine pesticide, lindane, as an example, Feng et al. (pages 207219) demonstrated the assembly of root-associated microbiota of rice varied with soil type, rice growth time [Detail] ...

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    Yan He, Peng Cai
    Yongxing Cui, Xia Wang, Xiangxiang Wang, Xingchang Zhang, Linchuan Fang

    •Ÿ Five methods of soil HM pollution evaluation based on enzyme activity were reviewed

    Ÿ•Ÿ This review examined the performance and ecological implications of these methods

    •ŸŸ Enzymatic stoichiometry methods reflect changes in soil functions under HM stress

    •ŸŸ Microbial metabolic limitation is a promising indicator to assess soil HM pollution

    Soil enzyme activities have been suggested as suitable indicators for the evaluation of metal contamination because they are susceptible to microbial changes caused by heavy metal stress and are strictly related to soil nutrient cycles. However, there is a growing lack of recognition and summary of the historic advancements that use soil enzymology as the proposal of evaluation methods. Here, we review the most common methods of heavy metal pollution evaluation based on enzyme activities, which include single enzyme index, combined enzyme index, enzyme-based functional diversity index, microbiological stress index, and ecoenzymatic stoichiometry models. This review critically examines the advantages and disadvantages of these methods based on their execution complexity, performance, and ecological implications and gets a glimpse of avenues to come to improved future evaluation systems. Indices based on a single enzyme are variable and have no consistent response to soil heavy metals, and the following three composite indices are characterized by the loss of many critical microbial processes, which thus not conducive to reflect the effects of heavy metals on soil ecosystems. Considering the dexterity of ecoenzymatic stoichiometry methods in reflecting changes in soil functions under heavy metal stress, we propose that microbial metabolic limitations quantified by ecoenzymatic stoichiometry models could be promising indicators for enhancing the reality and acceptance of results and further improving the potential for actual utility in environmental decision-making.

    Qing Zhang, Weiping Mei, Longfei Jiang, Qian Zheng, Chunling Luo, Gan Zhang

    • Mechanisms of soil sorption and plant uptake of OPFRs were measured.

    • Humid acids contribute to electrostatic interaction, hydrogen bonding, etc.

    • Hydrolysis is an important transformation behavior of OPFRs in the soil-plant system.

    • RCF showed no significant correlation with hydrophobicity of OPFRs in soil experiments.

    Organophosphate flame retardants (OPFRs), as a replacement for polybrominated diphenyl ethers (PBDEs), are of increasing concern due to their high production over the years. Soil is the major environmental reservoir and interchange for OPFRs. OPFRs in soil could be transferred to the food chain, and pose potential ecological and human health risks. This review focused on the environmental fate and effects of typical OPFRs in the soil-plant system. We concluded that the sorption and transformation behaviors of OPFRs due to their crucial impact on bioavailability. The root uptake and translocation of OPFRs by plants were summarized with analyses of their potential affecting factors. The in planta transformation and potential ecological effects of OPFRs were also briefly discussed. Finally, we highlighted several research gaps and provided suggestions for future research, including the development of simulative/computative methods to evaluate the bioavailability of OPFRs, the effects of root exudates and rhizosphere microorganisms on the bioavailability and plant uptake of OPFRs, and the development of green and sustainable technologies for in situ remediation of OPFRs-contaminated soil.

    Haijian Bing, Shaojun Qiu, Xin Tian, Jun Li, He Zhu, Yanhong Wu, Gan Zhang

    • Trace metal contamination in soils of 29 China’s mountains was investigated.

    • Cd was the priority control metal with moderate to heavy contamination.

    • Cd and Pb contamination were higher in northwest, south and southwest China.

    • Atmospheric deposition was the main sources of Cd and Pb in soils.

    • Climate, vegetation and soil properties regulated spatial distribution of trace metals.

    Trace metal contamination in soils is a threat with an uncertain limit to maintain planet safety, and the issue of trace metal contamination in mountain soils is still of low concerned. In this study, we assessed the contamination of six trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in mountain soils across China and deciphered the potential drivers of their spatial distribution. The results showed that concentrations of Cd and Pb decreased significantly with soil depth, and their concentrations were markedly higher in north-west, south, and south-west China than elsewhere. Among the metals, Cd was the priority for control with moderate to heavy contamination, followed by Pb, whereas the other metals did not show evident contamination. The altitudinal pattern and isotopic tracing revealed that the significant enrichment and marked contamination of Cd and Pb in surface soils were primarily attributed to deposition through long-range transboundary atmospheric transport and condensation. Ore mining, nonferrous smelting, and coal and fuel combustion were identified as primary anthropogenic sources of the Cd and Pb. Soil organic matter content, pH, and soil forming processes directly determined the accumulation of trace metals in the soils, and orographic effects, including local climate, vegetation composition, and canopy filtering, regulated the spatial distribution of the metals. This study highlights the significance of soil Cd contamination in mountains, which are considered of low concern, and suggests that long-term monitoring of trace metal contamination is necessary to improve biogeochemical models that evaluate the responses of the mountain critical zone to future human- and climate-induced environmental changes.

    Jiayin Feng, Ashley E. Franks, Zhijiang Lu, Jianming Xu, Yan He

    •Ÿ Rice microbiota responded to lindane pollutant was studied spatiotemporally.

    •ŸŸ Growth time, soil types and rhizo-compartments had significant influence.

    Ÿ Lindane stimulated the endosphere microbiota of rice which was highly dynamic.

    •ŸŸ Root–soil–microbe interactions induced an inhibited redox-coupled lindane removal.

    •ŸŸ This work was beneficial to better regulation of plant growth against adversity.

    Soil-derived microbiota associated with plant roots are conducive to plant growth and stress resistance. However, the spatio-temporal dynamics of microbiota in response to organochlorine pollution during the unstable vegetative growth phase of rice is not well understood. In this study, we focused on the rice (Oryza sativa L.) microbiota across the bulk soil, rhizosphere and endosphere compartments during the vegetative growth phase in two different soils with and without lindane pollutant. The results showed that the factors of growth time, soil types and rhizo-compartment had significant influence on the microbial communities of rice, while lindane mostly stimulated the construction of endosphere microbiota at the vegetative phase. Active rice root-soil-microbe interactions induced an inhibition effect on lindane removal at the later vegetative growth phase in rice-growth-dependent anaerobic condition, likely due to the root oxygen loss and microbial mediated co-occurring competitive electron-consuming redox processes in soils. Each rhizo-compartment owned distinct microbial communities, and therefore, presented specific ecologically functional categories, while the moderate functional differences were also affected by plants species and residual pollution stress. This work revealed the underground micro-ecological process of microbiota and especially their potential linkage to the natural attenuation of residual organochlorine such as lindane.

    Chong Liu, Mo-ming Lan, Er-kai He, Ai-jun Yao, Guo-bao Wang, Ye-tao Tang, Rong-liang Qiu

    • We compared the phenomic and exudate metabolomic responses of roots of two rice cultivars to Cd.

    • JY841 suffered serious root membrane damage and up-regulated phenylethanoid glycosides.

    • TY816 up-regulated lipids and fatty acids to actively cope with oxidative stress.

    • Reprogramming of root architecture and exudates contributed to contrasting Cd uptake.

    To cope with heavy metal stress, plant root systems undergo root structure modification and release of multifarious metabolites. Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants. Here two rice varieties with contrasting grain cadmium (Cd) accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis. The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress. The low-Cd accumulation rice cultivar (TY816) had a more highly developed root system that coped with Cd stress (10 μM) by maintaining high root activity, while the root cells of the high-Cd accumulation cultivar (JY841) lost viability due to excessive Cd accumulation. TY816 upregulated lipids and fatty acids to reduce Cd uptake, whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress. The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress. Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.

    Mingzhe Xu, Yongxing Cui, Jingzi Beiyuan, Xia Wang, Chengjiao Duan, Linchuan Fang

    • The microbial metabolism was limited by soil carbon (C) and phosphorus (P) under heavy metal stress.

    • The increase of heavy metal concentration significantly increased the microbial C limitation.

    • Heavy metal pollution can increase the loss of soil C by affecting microbial metabolism.

    • Microbial metabolism limitation can be used as a potential index to evaluate the toxicity of heavy metals.

    Heavy metals can exist in soil for a long time and seriously affect soil quality. The coexistence of various heavy metal pollutants leads to biotoxicity and alters the activity of microorganisms. Soil microbial metabolism plays an important role in nutrient cycling and biochemical processes of soil ecosystem. However, the effects of heavy metal contamination on microbial metabolism in soil are still unclear. This study aims to reveal the responses of microbial metabolic limitation to heavy metals using extracellular enzyme stoichiometry, and further to evaluate the potential impacts of heavy metal pollution on soil nutrient cycle. The results showed that soil microbial metabolism reflected by the ecoenzymatic activities had a significant response to soil heavy metals pollution. The metabolism was limited by soil carbon (C) and phosphorus (P) under varied heavy metal levels, and the increase of heavy metal concentration significantly increased the microbial C limitation, while had no effect on microbial P limitation. Microorganisms may increase the energy investment in metabolism to resist heavy metal stress and thus induce C release. The results suggest that energy metabolism selected by microorganisms in response to long-term heavy metal stress could increase soil C release, which is not conducive to the soil C sequestration. Our study emphasizes that ecoenzymatic stoichiometry could be a promising methodology for evaluating the toxicity of heavy metal pollution and its ecological effects on nutrient cycling.

    Fuhao Liu, Xunrong Huang, Hanghang Zhao, Xiongfei Hu, Lu Wang, Xin Zhao, Pengcheng Gao, Puhui Ji

    • After modification, the adsorption capacity of fly ash to heavy metals is enhanced.

    • Modified fly ash has significant effect on stabilization of Cadmium and lead.

    • The activity of heavy metals stabilized after 6 months of operation of the column.

    • DOC, pH, and organic matter play an important role in heavy metal remediation.

    This study investigated the stabilization of heavy metals by adding modified fly ash (FA) to contaminated soils, and two similar materials, NaOH-zeolite (ZE) and natural zeolite (ZO) were introduced into the soils for comparison. Column leaching tests were conducted to analyze the difference of stabilization effects between the three materials. Leaching columns were run for 6 months, and a considerable stabilization of heavy metals in the soils was observed. The concentration of cadmium (Cd) and lead (Pb) in the amended soil substantially decreased (p<0.05). The results indicated that after 11 weeks of column leaching, Cd and Pb concentrations in the soil leachate decreased to below the detection limit due to amendment stabilization. Among the three amendments, the ZE amendment showed the optimum capacity for heavy metal immobilisation in the soils. In addition, after 6 months of leaching, Pb and Cd concentrations in the soils with the three different amendments decreased to various degrees. The amendments of modified FA and ZE were better than those of natural ZO. Coal FA, after modification, is a useful amendment for the remediation of heavy metals in the contaminated soil.

    Jipeng Luo, Jiabin Liang, Yuchao Song, Xinyu Guo, Youzheng Ning, Nanlin Liu, Heping Zhao, Tingqiang Li

    • Cd extractability of eleven kinds of fruit residue extractions was compared.

    • The most effective volume ratio of LRE, GLDA and tea saponin in Cd phytoextraction was 15:4:1.

    • CPC improved plant growth, Cd phytoextraction performance and soil organic matter content.

    • CPC induced less changes in bacterial community composition and had no evident influence on MBC and bacterial α-diversity.

    A chelating agent is known as the enhancer for metal phytoextraction; however, there is still a lack of efficient and environmentally sustainable chelators. Here, lemon residue extraction (LRE), prepared from 11 kinds of fruit wastes, was combined with N, N-bis (carboxymethyl) glutamic acid (GLDA), and tea saponin (T.S.) for the compounded plant-derived chelator (CPC), and their influences on Cd phytoextraction by the hyperaccumulator Sedum alfredii was evaluated. Among these fruits, the lemon residue extracted the most significant amount of Cd from the soil. The most effective CPC was at the volume ratio of three agents being 15:4:1 (LRE: GLDA: T.S.). Compared with the deionized water, the solubility of three Cd minerals was increased by 36~311 times, and Cd speciation was substantially altered after CPC application. In the pot experiment, CPC addition caused evident increases in plant shoot biomass, Cd phytoextraction efficiency, and organic matter content compared with EDTA and nitrilotriacetic acid (NTA) application. CPC induced fewer changes in bacterial community composition compared with EDTA and had no pronounced influence on microbial biomass carbon and bacterial α-diversity, suggesting CPC had a subtle impact on the microbiological environments. Our study provides a theoretical base for the reutilization of fruit wastes and the development of environmental-friendly chelator that assists Cd phytoextraction.

    Shaowen Xie, Fei Wu, Zengping Ning, Manjia Chen, Chengshuai Liu, Qiang Huang, Fangyuan Meng, Yuhui Liu, Jimei Zhou, Yafei Xia

    • Remediated soil treated by thermal curing exhibited strong inherent resistance to acidic attack with the formation of ZnCr2O4 spinel.

    • A two-step calculation method to calculate the sum of the leaching and acid-soluble fraction contents of heavy metals in remediated soils for risk evaluation have been proposed.

    • Compared with the traditional one-step calculation method, this two-step calculation method can effectively avoid underestimating the risk of remediated soils.

    The centralized utilization of heavy-metal-contaminated soil has become the main strategy to remediate brownfield-site pollution. However, few studies have evaluated the ecological and human health risks of reusing these remediated soils. Considering Zn as the target metal, systematic pH-dependent leaching and the Community Bureau of Reference (BCR) extraction were conducted at six pH values (pH= 2, 4, 6, 8, 10, 12) for the remediated soil treated through thermal curing. The pH-dependent leaching results showed that with the formation of ZnCr2O4 spinel phases, the remediated soil exhibited strong inherent resistance to acidic attack over longer leaching periods. Furthermore, the BCR extraction results showed that the leaching agent pH value mainly affected the acid-soluble fraction content. Moreover, a strong complementary relationship was noted between the leaching and acid-soluble fraction contents, indicating that the sum of these two parameters is representative of the remediated soil risk value. Therefore, we proposed a two-step calculation method to determine the sum of the two heavy metal parameters as the risk value of remediated soil. In contrast to the traditional one-step calculation method, which only uses the leaching content as the risk value, this two-step calculation method can effectively avoid underestimating the risk of remediated soil.

    Xiaoming Wan, Mei Lei, Tongbin Chen

    •Ÿ Hawk moth showed foraging preference to P. vittata fronds with low As concentation.

    •Ÿ Hawk moth can not exclude As by excretion.

    •Ÿ The main As speciation of hawk moth is As(III)-SH.

    The development of an effective and green bioinsecticide is a research hotspot. This study demonstrated the possibility of using an arsenic (As) hyperaccumulator as a bioinsecticide. When the As concentration in the Pteris vittata fronds exceeded 138 mg kg−1, the larva of the hawk moth (Theretra clotho) displayed apparent preference to lower-As-concentration P. vittata fronds. The As concentration in the larva body was as high as 850 mg kg–1 Such high concentration of As in the larva body might have been the case that T. clotho lacks a process to exclude As. The larval frass showed an As concentration of only 1%–4% of that in the larva body. The predominant As species in the larva body and frass was As(III)-SH. The percentage of As(III)-SH was slightly higher in the frass than that in the larval body. Chelation with thiols may be a universal detoxification mechanism for As in both plants and insects. In general, the adoption of P. vittata as a bioinsecticide should be feasible. However, the exact processes to achieve this goal still need further study. The mechanism of different animals to detoxify As is another interesting research topic.