Effects of rare earth and acid rain pollution on plant chloroplast ATP synthase and element contents at different growth stages

Elucidation of the stress mechanisms on activated sludge stability induced by yttrium oxide nanoparticles with cytotoxicity: Performance deterioration, biointerface variation and microbial response

As technoscience advances, widespread use of nanoparticles (NPs) has resulted in environmental risks. This study focuses on the potential stress of 0-200 mg/L yttrium oxide (Y2O3) NPs on the activated sludge stability. Y2O3 NPs progressively suppressed nitrification, caused significant NO2- accumulation (200 mg/L) and diminished activities of key functional enzymes. Deteriorated flocculation corroborates the Y2O3 NPs' destruction. Extracellular polymeric substances were lessened, yet amplified microbial metabolites prove the microbial counteraction coping with Y2O3 NPs' cytotoxicity. Plausible blockage of different protein channels contributed to the wane in biological nitrogen-removal capacity. Plus, 50 mg/L Y2O3 NPs stimulated the β-glucan production. When exceeding 100 mg/L, plentiful Y2O3 NPs aggregate on sludge-surface, which inhibits nutrients transfer and metabolism. Furthermore, ammonia-oxidizing bacteria shifted from Nitrosomonas to Nitrosospira with Y2O3 NPs increase. Reduction in Nitrospira, Saccharimonada-genera, and Microlunatus further corroborates the impairment of pollutants removal. PICRUSt2 prediction demonstrates Y2O3 NPs impedes nitrogen and glycolytic metabolic pathway.

Metabolomics reveals the potential mechanism of La(III) promoting enrichment of Sodium hydrogen arsenate and Roxarsone in Solanum nigrum L

The rare earth element lanthanum (La(III)) has been found to effectively enhance crop yields and improve plant growth and development. Arsenic (As), as a class of toxic metals widely found in the environment, poses a serious threat to both ecological and human health. Research on the application of La(III) in phytoremediation to enhance remediation efficiency is currently lacking. This study examined the impact of La(III) on physiological and biochemical indicators of Solanum nigrum L. (S. nigrum) exposed to Sodium hydrogen arsenate (SA) and Roxarsone (ROX) treatments under hydroponic conditions. Results indicated that La(III) treatment increased S. nigrum's aboveground As transport capacity by 58.68 %-213 % compared to no La(III) application. Additionally, foliar spraying of La(III) significantly inhibited the expression of toxic metabolites in the root system of S. nigrum, reducing Benzamide by 99.79 % under SA treatment and ZON by 87.72 % under ROX treatment. La(III) is likely to promote the transport of toxins and nutrients within and out of cells by activating ABC transporters, thereby enhancing S. nigrum's arsenic tolerance and metabolic activity. These findings provide molecular-scale insights into La(III) enhancement of the resilience of hyper-enriched plants and the remediation potential of contaminated sites.

Biostimulant Response of Foliar Application of Rare Earth Elements on Physiology, Growth, and Yield of Rice

Rare earth elements (REEs) have been intentionally used in Chinese agriculture since the 1980s to improve crop yields. Around the world, REEs are also involuntarily applied to soils through phosphate fertilizers. These elements are known to alleviate damage in plants under abiotic stresses, yet there is no information on how these elements act in the physiology of plants. The REE mode of action falls within the scope of the hormesis effect, with low-dose stimulation and high-dose adverse reactions. This study aimed to verify how REEs affect rice plants' physiology to test the threshold dose at which REEs could act as biostimulants in these plants. In experiment 1, 0.411 kg ha-1 (foliar application) of a mixture of REE (containing 41.38% Ce, 23.95% La, 13.58% Pr, and 4.32% Nd) was applied, as well as two products containing 41.38% Ce and 23.95% La separately. The characteristics of chlorophyll a fluorescence, gas exchanges, SPAD index, and biomass (pot conditions) were evaluated. For experiment 2, increasing rates of the REE mix (0, 0.1, 0.225, 0.5, and 1 kg ha-1) (field conditions) were used to study their effect on rice grain yield and nutrient concentration of rice leaves. Adding REEs to plants increased biomass production (23% with Ce, 31% with La, and 63% with REE Mix application) due to improved photosynthetic rate (8% with Ce, 15% with La, and 27% with REE mix), favored by the higher electronic flow (photosynthetic electron transport chain) (increase of 17%) and by the higher Fv/Fm (increase of 14%) and quantum yield of photosystem II (increase of 20% with Ce and La, and 29% with REE Mix), as well as by increased stomatal conductance (increase of 36%) and SPAD index (increase of 10% with Ce, 12% with La, and 15% with REE mix). Moreover, adding REEs potentiated the photosynthetic process by increasing rice leaves' N, Mg, K, and Mn concentrations (24-46%). The dose for the higher rice grain yield (an increase of 113%) was estimated for the REE mix at 0.72 kg ha-1.

Foliar application of lanthanum promotes growth and phytoremediation potential Solanum nigrum L

The hormetic effect of rare earth elements (REEs) has been found in a variety of crops and has been promoting crop growth for decades. Spraying leaves with REEs can enhance the endocytosis of plant roots. The non-selectivity of endocytosis is conducive to the direct absorption of environmental pollutants. The hyperaccumulator Solanum nigrum L. (S. nigrum), as a plant with high biomass and heavy metal tolerance, is a good candidate for phytoremediation. La(III), as a typical light REE, also has an obvious hormetic effect on S. nigrum. At 10 μM La(III), the biomass of S. nigrum reached the maximum, which was 89% greater than the control, and La(III) concentration was much lower than the previously reported optimum of 56 μM for general plants. In the present study, enhanced endocytosis after foliar spraying of La(III) was firstly observed in the root cell of hyperaccumulation plants, and La(III) increased the biomass of S. nigrum by improving the photosynthetic system, and promoting nutrient uptake and root development. The antioxidant defense system improved by La(III) contributed to the tolerance of S. nigrum to heavy metals. Applying a reasonable range of La(III) is beneficial to improving S. nigrum growth and tolerance of heavy metals. Compared with spraying deionized water, the translocation factor and bioaccumulation factor value of S. nigrum to cadmium increased by 15% and 21% respectively when spraying 10 μM La(III). Our findings provide a reference for improving hyperaccumulator plant growth and biomass, which improves phytoremediation efficiency.

Improving yield and quality of rice under acid rain stress by regulating nitrogen assimilation with exogenous Ca2

Acid rain threatens crop yield and nutritional quality, and Ca²⁺ can regulate plant responses to abiotic stresses. To improve the yield and nutritional quality of crops under acid rain stress, we applied exogenous Ca²⁺ to regulate nitrogen assimilation in rice seedlings under simulated acid rain stress (pH 4.5 or 3.0), taking yield and nutritional quality of rice as evaluation criteria. We found that Ca²⁺ (5 mM) maintained the total nitrogen content of rice at the seedling and booting stages to alleviate the inhibitory effect of simulated acid rain on rice yield. Meanwhile, Ca²⁺ improved the activity of glutamate synthase to eliminate the disruption of glutamine synthetase/glutamate synthase balance under simulated acid rain. It decreased the efficiency of nitrogen assimilation, thereby reducing the inhibition of essential amino acid content in rice. The mitigation effect on simulated acid rain at pH 4.5 was better than that of simulated acid rain at pH 3.0. Overall, Ca²⁺ may reduce the negative effect of acid rain on the yield and nutritional quality of crops.

Ploidy level enhances the photosynthetic capacity of a tetraploid variety of Acer buergerianum Miq

Background

Polyploidy plays an important role in plant breeding and has widespread effects on photosynthetic capacity. To determine the photosynthetic capacity of the tetraploid variety Acer buergerianum Miq. ‘Xingwang’, we compared the gas exchange parameters, chloroplast structure, chlorophyll contents, and chlorophyll fluorescence parameters between the tetraploid Acer buergerianum ‘Xingwang’ and the diploid ‘S4’. To evaluate the effects of genome duplication on the photosynthetic capacity of Acer buergerianum ‘Xingwang’, the transcriptomes of the autotetraploid ‘Xingwang’ and the diploid ‘S4’ of A. buergerianum were compared.

Methods

The ploidy of Acer buergerianum ‘Xingwang’ was identified by flow cytometry and the chromosome counting method. An LI-6800 portable photosynthesis system analyzer was used to assess the gas exchange parameters of the tetraploid variety ‘Xingwang’ and diploid variety ‘S4’ of A. buergerianum. We used a BioMate 3S ultraviolet-visible spectrophotometer and portable modulated fluorometer to measure the chlorophyll contents and chlorophyll fluorescence parameters, respectively, of ‘Xingwang’ and ‘S4’. Illumina high-throughput sequencing technology was used to identify the differences in the genes involved in the photosynthetic differences and determine their expression characteristics.

Results

The single-cell DNA content and chromosome number of the tetraploid ‘Xingwang’ were twice those found in the normal diploid ‘S4’. In terms of gas exchange parameters, the change in stomatal conductance, change in intercellular CO₂ concentration, transpiration rate and net photosynthetic rate of ‘Xingwang’ were higher than those of the diploid ‘S4’. The chlorophyll contents, the maximal photochemical efficiency of PSII and the potential photochemical efficiency of PSII in ‘Xingwang’ were higher than those of ‘S4’. The chloroplasts of ‘Xingwang’ contained thicker thylakoid lamellae. By the use of Illumina sequencing technology, a total of 51,807 unigenes were obtained; they had an average length of 1,487 nt, and the average N50 was 2,034 nt. The lengths of most of the unigenes obtained ranged from 200–300 bp, with an average value of 5,262, followed by those longer than 3,000 bp, with an average value of 4,791. The data revealed numerous differences in gene expression between the two transcriptomes. In total, 24,221 differentially expressed genes were screened, and the percentage of differentially expressed genes was as high as 46.75% (24,224/51,807), of which 10,474 genes were upregulated and 13,747 genes were downregulated. We analyzed the key genes in the photosynthesis pathway and the porphyrin and chlorophyll metabolism pathway; the upregulation of HemB may promote an increase in the chlorophyll contents of ‘Xingwang’, and the upregulation of related genes in PSII and PSI may enhance the light harvesting of ‘Xingwang’, increasing its light energy conversion efficiency.

Low-dose lanthanum activates endocytosis, aggravating accumulation of lanthanum or/and lead and disrupting homeostasis of essential elements in the leaf cells of four edible plants

Rare earth elements (REEs) are emerging as a serious threat to ecological safety due to their increasing accumulation in environments. The accumulation of REEs in environments has significantly increased its accumulation in the leaves of edible plants. However, the accumulation pathway of REEs in the leaves of edible plants are still unknown. In this study, lanthanum [La(III), a widely used and accumulated REE] and four edible plants (soybean, lettuce, pakchoi, and celery) with short growth cycles were selected as research objects. By using interdisciplinary research techniques, we found that low-dose La(III) activated endocytosis (mainly the clathrin-mediated endocytosis) in the leaf cells of four edible plants, which provided an accumulation pathway for low-dose La in the leaf cells of these edible plants. The accumulation of La in the leaf cells was positively correlated with the intensity of endocytosis, while the intensity of endocytosis was negatively correlated with the density of leaf trichomes. In addition to the accumulation of La, low-dose La(III) also brought other risks. For example, the harmful element (Pb) can also be accumulated in the leaf cells via La(III)-activated endocytosis; the homeostasis of the essential elements (K, Ca, Fe, Mg) was disrupted, although the chlorophyll synthesis and the growth of these leaf cells were accelerated; and the expression of stress response genes (GmNAC20, GmNAC11) in soybean leaves was increased. These results provided an insight to further analyze the toxicity and mechanism of REEs in plants, and sounded the alarm for the application of REEs in agriculture.

Causal Analysis of Ecological Impairment in Land Ecosystem on a Regional Scale: Applied to a Mining City Daye, China

We adopted a weight of evidence approach to establish a causal analysis of an impaired land ecosystem on a regional scale; namely, Daye, a traditional mining city in China. Working processes, including problem statements, a list of candidate causes, and a conceptual model were developed to represent a causal hypothesis for describing land degradation. Causal criteria were applied to integrate multiple lines of evidence. Then, various pieces of evidence were scored to either strengthen or weaken our causal assumptions. Results showed that habitat alteration, heavy metal accumulation, organic pollutants, water eutrophication, and nutrient runoff were the probable causes of land ecosystem impairment in Daye. Meanwhile, noxious gas, toxicants, altered underground runoff, atmospheric deposition, and acid rain were identified as possible causes. The most unlikely causes were altered hydrology, altered earth surface runoff, and soil erosion. Soil salinization, soluble inorganic salts, biological species invasion, and pathogens were deferred as delayed causes due to lack of adequate information. The causal analysis approach was applied to identify the primary causes of land degradation and implement accurate protective measures in an impaired land ecosystem.

Proteomic analysis reveals key proteins involved in ethylene-induced adventitious root development in cucumber (Cucumis sativus L.)

The mechanisms involved in adventitious root formation reflect the adaptability of plants to the environment. Moreover, the rooting process is regulated by endogenous hormone signals. Ethylene, a signaling hormone molecule, has been shown to play an essential role in the process of root development. In the present study, in order to explore the relationship between the ethylene-induced adventitious rooting process and photosynthesis and energy metabolism, the iTRAQ technique and proteomic analysis were employed to ascertain the expression of different proteins that occur during adventitious rooting in cucumber (Cucumis sativus L.) seedlings. Out of the 5,014 differentially expressed proteins (DEPs), there were 115 identified DEPs, among which 24 were considered related to adventitious root development. Most of the identified proteins were related to carbon and energy metabolism, photosynthesis, transcription, translation and amino acid metabolism. Subsequently, we focused on S-adenosylmethionine synthase (SAMS) and ATP synthase subunit a (AtpA). Our findings suggest that the key enzyme, SAMS, upstream of ethylene synthesis, is directly involved in adventitious root development in cucumber. Meanwhile, AtpA may be positively correlated with photosynthetic capacity during adventitious root development. Moreover, endogenous ethylene synthesis, photosynthesis, carbon assimilation capacity, and energy material metabolism were enhanced by exogenous ethylene application during adventitious rooting. In conclusion, endogenous ethylene synthesis can be improved by exogenous ethylene additions to stimulate the induction and formation of adventitious roots. Moreover, photosynthesis and starch degradation were enhanced by ethylene treatment to provide more energy and carbon sources for the rooting process.

Rare-earth element scandium improves stomatal regulation and enhances salt and drought stress tolerance by up-regulating antioxidant responses of Oryza sativa

Oryza sativa L. cv. Gönen grown in hydroponic culture was treated with scandium (Sc; 25 and 50 μM) alone or in combination with salt (100 mM NaCl) and/or drought (5% PEG-6000). Stress caused a decrease in growth (RGR), water content (RWC), osmotic potential (ΨΠ), chlorophyll fluorescence (Fv/Fm) and potential photochemical efficiency (Fv/Fo). Sc application prevented the decreases of these parameters. Sc also alleviated the changes on gas exchange parameters (carbon assimilation rate (A), stomatal conductance (gs), intercellular CO2 concentrations (Ci), transpiration rate (E) and stomatal limitation (Ls)). Stress caused no increase in superoxide dismutase (SOD) activity. After induvial applied NaCl or PEG, catalase (CAT) and ascorbate peroxidase (APX) showed an enhancement in activation and tried to scavenge of hydrogen peroxide (H2O2). On the other hand, in plants with the combination form of NaCl and PEG, only CAT activity was induced. Sc applications to NaCl-treated rice led to an increase of SOD, APX, glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) as well as peroxidase (POX). Sc under NaCl could be maintained both ascorbate (AsA) and glutathione (GSH) regeneration. Despite of induction of MDHAR and DHAR under Sc plus PEG, Sc did not maintain AsA redox state because of no induction in APX activity. However, GSH pool could be regenerated by induction in DHAR and GR in this group. Sc application (especially for 25 μM) in rice exposed to NaCl + PEG resulted an enhancement in APX and MDHAR and so Sc could be partially provided AsA regeneration. Since no increases in DHAR and GR were observed, GSH pool was reduced. Due to this activation of antioxidant enzymes, stress-induced H2O2 and TBARS content (lipid peroxidation) significantly decreased in rice with Sc applications. Sc in plants with stress also increased the transcript levels of OsCDPK7 and OsBG1 related to stomatal movement and signaling pathway. Consequently, Sc protected the rice plants by minimizing disturbances caused by NaCl or PEG exposure via the AsA-GSH redox-based systems.

Effects of heavy rare earth element (yttrium) on partial-nitritation process, bacterial activity and structure of responsible microbial communities

Yttrium (Y(III)) is mined commercially for industrial purposes due to its excellent physical properties. However, the effects of Y(III) in mining-wastewater on the performance of partial-nitritation process and ammonia-oxidizing bacteria (AOB) have not been explored. To elucidate Y(III) effects on biological mechanisms, kinetics was conducted to establish a correlation between Y(III) dosage and specific-oxygen-uptake-rate (SOUR). The mechanism(s) demonstrated by bacterial population to resist against toxic effects from Y(III) dose was also investigated using scanning electron microscopy-(SEM), energy-dispersive X-ray spectroscopy-(EDS), confocal laser scanning microscopy-(CLSM)，Fourier transform infrared-(FTIR) spectroscopy, and 2-dimensional correlation infrared-(2DCOS-IR) approach. The study revealed a strong correlation between ammonium oxidation rate (AOR) and Y(III) dosage. AOR promotion was more pronounced when Y(III) concentration was ≤20 mg/L (maximum AOR of 12.39 mgN/L/h, at 5 mg/L), whereas inhibition when Y(III) in influent was >20 mg/L (minimum AOR of 7.34 mgN/L/h, at 500 mg/L). Aiba model demonstrated high-performance (R² = 0.962) when Y(III) concentration ranged 0-20 mg/L, whereas linear model fitted well (R² of 0.984) to experimental data when Y(III) dose ranged 20-500 mg/L. The maximum change in SOUR (Vmax), half-rate constant (Km), and inhibition constant (Ki) reached 1.04 d^-1, 20.12 mg/L, and 4.87 mg/L, respectively, an indication that dosage of Y(III) could affect the partial-nitritation process. SEM-EDS showed that the content of extracellular polymeric substances (EPS) increased along with increasing Y(III) dosage. When 20 mg/L of Y(III) was dosed, the fraction of Y(III) within the surface elemental composition of the sludge increased gradually whereas that of calcium decreased. To further comprehend the EPS production, CLSM results further revealed β-polysaccharide as the dominant component in the EPS. FTIR/2DCOD-IR showed that the chelation of polyguluronic sections within β-polysaccharide, together with hydrazine might be the main pathways of cell resistance, but β- glucan, may have caused the hormesis.

Aging Mechanism and Properties of SBS Modified Bitumen under Complex Environmental Conditions

Bitumen aging can lead to the deterioration of asphalt pavement performance, shortening the service life of road. In order to solve the problem that current studies on the ultraviolet (UV) aging of bitumen either ignore the effects of natural environmental conditions or only consider the effects of water. In this study, different aqueous media and UV coupled simulated aging tests were carried out on virgin bitumen and styrene butadiene styrene (SBS) modified bitumen in a UV environment chamber. The combination of macroscopic performance tests and microstructure tests was used to analyze the physical, rheological, and microstructure changes of virgin bitumen and SBS modified bitumen after The film oven test (TFOT) aging and UV aging in different environments (UV, UV + Water, UV + Acid, UV + Salt). Dynamic shear rheometer (DSR) results indicated that UV aging results in the increase of rutting factor and the improvement of rutting resistance at high temperature. The Fourier transform infrared spectrum (FTIR) results illustrated that the bitumen would be oxidized and SBS would be degraded under ultraviolet radiation. The four-component analysis test results showed that light component migrated to the heavy component during the aging process. Moreover, water will aggravate the UV aging of bitumen, and the presence of acid or salt worsens ultraviolet aging.

Ecological risk assessment of cerium for tropical agroecosystems

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC₅ = 281.6 mg Ce kg^-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

Arabinogalactan Proteins Are the Possible Extracellular Molecules for Binding Exogenous Cerium(III) in the Acidic Environment Outside Plant Cells

Rare earth elements [REE(III)] increasingly accumulate in the atmosphere and can be absorbed by plant leaves. Our previous study showed that after treatment of REE(III) on plant, REE(III) is first bound by some extracellular molecules of plant cells, and then the endocytosis of leaf cells will be initiated, which terminates the endocytic inertia of leaf cells. Identifying the extracellular molecules for binding REE(III) is the crucial first step to elucidate the mechanism of REE(III) initiating the endocytosis in leaf cells. Unfortunately, the molecules are unknown. Here, cerium(III) [Ce(III)] and Arabidopsis served as a representative of REE(III) and plants, respectively. By using interdisciplinary methods such as confocal laser scanning microscopy, immune-Au and fluorescent labeling, transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy, circular dichroism spectroscopy, fluorescent spectrometry and molecular dynamics simulation, we obtained two important discoveries: first, the arabinogalactan proteins (AGP) inside leaf cells were sensitively increased in protein expression and recruited onto the plasma membrane; second, to verify whether AGP can bind to Ce(III) in the acidic environment outside leaf cells, by choosing fasciclin-like AGP11 (AtFLA11) as a representative of AGP, we found that Ce(III) can form stable [Ce(H2O)7](III)-AtFLA11 complexes with an apparent binding constant of 1.44 × 10-6 in simulated acidic environment outside leaf cells, in which the secondary and tertiary structure of AtFLA11 was changed. The structural change in AtFLA11 and the interaction between AtFLA11 and Ce(III) were enhanced with increasing the concentration of Ce(III). Therefore, AtFLA11 can serve as Lewis bases to coordinately bind to Ce(III), which broke traditional chemical principle. The results confirmed that AGP can be the possible extracellular molecules for binding to exogenous Ce(III) outside leaf cells, and provided references for elucidating the mechanism of REE(III) initiating the endocytosis in leaf cells.

Exogenous application of Ca2+ mitigates simulated acid rain stress on soybean productivity and quality by maintaining nutrient absorption

Acid rain is a global environmental problem that threatens agricultural production. Calcium (Ca), as a signal substance for physiological activities, has been known to regulate plant growth under abiotic stresses. To clarify whether calcium could be one of possible ways to alleviate the reduction caused by acid rain in agricultural production and investigate its regulating mechanism on adaptation of plants under acid rain stress, we studied the effect of exogenous Ca2+ (5 mM CaCl2) on growth of soybean at different growth stages (seedling, flowering-podding, and filling stages) as well as yield and grain quality of soybean under simulated acid rain (pH 4.5 or pH 3.0) stress. We found that the application of Ca2+ could regulate the activity of plasma membrane H+-ATPase, for mitigating the increase of ammonium and the decrease of nitrate and phosphorus in soybean roots, which mitigated the inhibition on growth and improved the yield and grain quality of soybean under simulated acid rain stress. In addition, the alleviating effect of exogenous Ca2+ on soybean was the most significant at seedling stage. The results indicate that the exogenous Ca2+ could enhance the adaptation of soybean and facilitate the recovery of soybean productivity and grain quality under simulated acid rain stress by maintaining the uptake of nitrate, ammonium, and phosphorus.

Analysis for effects of lanthanum (III) on the aboveground modules and respiration of soybean populations

The accumulation of rare earth elements (REEs) in the environment has become an environmental safety issue that cannot be ignored. However, previous studies on the environmental risks of REEs have mostly been performed at the individual level. In this work, to explore the effects of REE pollution at the population level, the effects of lanthanum (III) [La(III)] on the aboveground modules of soybean (Glycine max L) populations at different planting densities were investigated by simulating La(III) pollution, and the underlying mechanism was revealed on the physiological and biochemical levels of respiration. The results showed that the addition of 0.4 and 1.2 mM La(III) decreased the aboveground module growth parameters of the soybean populations, and this effect was more evident in the 1.2 mM La(III) treatment. At a certain dose of La(III), the effects of La(III) on the aboveground module growth parameters decreased with increasing plant densities. In addition, the effects of La(III) on the aboveground module growth parameters of soybean plants at different planting densities were related to plant respiration, in particular, to changes in the activities of respiratory key enzymes. The results indicated that the inhibitory effects of La(III) depended on the dose and on the planting density. This finding could provide a novel perspective and a basis for the objective assessment of potential environmental risks of REEs. ONE SENTENCE SUMMARY: La(III) pollution effects on the aboveground modules of soybean populations are related to the changes of the population respiration and the respiratory key enzymes; moreover, these effects are restricted by the population density.

Evaluation and Policy Research on the Sustainable Development of China’s Rare Earth Resources

As rare earth resources are indispensable raw materials for modern society, they have become strategic global reserve resources. Even though China is the world’s largest producer and exporter of rare earth, the industry has low efficiency and severe problems with over-exploitation and environmental pollution; therefore, there needs to be a greater focus on the sustainable exploitation of rare earth resources. This paper establishes an innovative evaluation index system for the sustainable development of China’s rare earth resources from six main aspects; economic development, social progress, environmental protection, technological innovation, rare earth development and utilization, and rare earth protection in which the indicators are assessed using an entropy method. Grey correlation analysis was used to evaluate China’s rare earth sustainable development level from 2006–2016, from which it was found that sustainable development was poor from 2006–2010 and marginally better from 2011–2016. The main factor affecting rare earth sustainable development in China was found to be the lag in the development of environment protection system and rare earth protection system. Policy recommendations for improving China’s rare earth protection, environmental protection, and technological innovation are proposed to guide government regulations and assist rare earth industry personnel.

A novel evaluation of the effect of lanthanum exposure on plant populations

The accumulation of rare earth elements (REEs) in the environment has recently become a new environmental problem. There have been many studies about the effects of REEs on plant at the individual, organ, cellular and genetic levels. Plants exist in populations under natural conditions, but little is known about the effects of REEs on plant populations. In this study, the effects of lanthanum (III) [La(III)] on the root module growth of soybean (Glycine max L) populations at different densities were investigated by simulating La(III) pollution. Results showed that at La(III) concentrations of 0.40 and 1.20 mM, both the root module growth parameters and leaf photosynthesis parameters were decreased, with 1.20 mM of La(III) causing a more significant decrease. In addition, the above parameters in low-density soybean populations decreased more significantly than those in high-density soybean populations. The above results show that the inhibitory effects of 0.40 and 1.20 mM of La(III) on the growth of root modules are closely related to the inhibition of photosynthesis in soybean population. Moreover, the inhibitory effect of La(III) on the growth of root modules of soybean population is enhanced as the La(III) concentration increases, while is weakened as plant population density increases. This study would provide a reference for the further research on the ecotoxicology of REEs, and show a new perspective and basis for the objective assessment of the environmental risks of REEs.

ONE SENTENCE SUMMARY

La(III) pollution affects the root module growth and photosynthesis in soybean populations, and the effects vary depending on soybean population densities.