As the highest and largest plateau in the world, the Qinghai-Tibet Plateau (QTP) covers wide geological, topographical and climatic gradients and thus acts as a major center for biodiversity and houses a diverse array of high elevation ecosystems. Together these factors make the QTP a critical ecological shield for Asia. However, the composition, structure and function of plant diversity in QTP has experienced profound changes in recent decades. Long-term on-site monitoring, field experiments, remote sensing, and simulations have led to significant advances in our understanding of how plant diversity on the QTP has responded to climate change and human activity. This review synthesizes findings from previous researches on how climate change and human activity have impacted plant diversity on the QTP. We identify gaps in our knowledge and highlight the need for interdisciplinary studies, long-term monitoring networks, and adaptive management strategies to enhance our knowledge and safeguard the QTP’s biodiversity amid accelerating global climate change.

Policies on the management of paddy fields are usually made at a broad scale and from a long-term perspective, while predicting the spatial extent of cadmium (Cd) contamination in paddy soils remains challenging. In this study, we developed a process-driven spatial model to quantify the transport of Cd in paddy soils and validated it against observed data from a 10-year regional investigation in southern China. Using a geographic information system and Monte Carlo simulation, the model was then applied to evaluate the effectiveness of different remediation strategies for contaminated paddy fields at field-to-regional scales in a 100-year period. In the last decade, atmospheric emissions have accounted for 43.5 % of the total Cd input in local paddy soils. However, the local clean air act failed to mitigate Cd contamination in 99.8 % of study area over the period of 2020-2120 because straw return became the dominant contributor to Cd inputs. Improving aerosol emission reductions by 3 % per year, stopping straw return to soil, and cleaning irrigation channels would take approximately 30 years (2020-2050) to protect 95 % of local rice production from causing an excessive human Cd kidney burden, especially in the paddy fields located in mining-affected areas.

[Objective]This study aims to to understand the adsorption characteristics and mechanisms of Plumbum(Pb)and cadmium(Cd)elements,which have strong pollution toxicity,in Guizhou yellow soil,thus providing theoretical basis for the prevention and control of heavy metal Pb and Cd pollution in agricultural soil.[Method]Basalt parent yellow soil from different sites in Guizhou Province was selected as the research object.According to the relevant formulas of the 1-site/2-p Ka Generalized Complex Surface Complexation Model(SCM)theory,combined with soil physicochemical property determination experiments,potentiometric titration experiments,and Pb and Cd adsorption edge experiments,the surface acid-base property parameters,namely model parameters,of yellow soil were obtained.Then,using the 1-site/2-p Ka SCM,the morphological distribution of three active sites on the yellow soil surface and the adsorption behavior of Pb and Cd at different pH levels were simulated to explore the adsorption characteristics and mechanisms of Pb and Cd by yellow soil.Correlation analysis was conducted to analyze factors influencing the adsorption of Pb and Cd by yellow soil.[Result]According to the relevant formulas of the SCM theory,the charge zero pHpzc,SCM of the four yellow soil samples were obtained as 5.040,5.549,7.984,and 4.297,respectively.The surface site concentrations(Hs)were 0.137,0.183,0.181,and 0.308 mol/kg,and the surface site densities(Ds)were 4.519,2.571,2.122,and 3.664 sit/nm2,respectively.Changes in the forms of ≡SOH2+,≡SOH,and ≡SO-on the yellow soil surface under different pH conditions were simulated by SCM,and the adsorption mechanisms of Pb and Cd on the yellow soil surface were preliminarily explained.The adsorption behavior of Pb and Cd on the yellow soil surface was fitted at different pH levels(correlation coefficient R≥0.96),indicating that SCM was suitable for describing the adsorption characteristics of Pb and Cd on the yellow soil surface.Adsorption edge experiments showed that the initial concentrations of Pb、Cd and the pH of the soil environment both affect the adsorption behavior of Pb and Cd on the yellow soil surface,and there are differences in the adsorption of Pb and Cd on the yellow soil surface;The adsorption capacity of yellow soil for Pb was greater than that for Cd,which was not only due to Pb having a smaller hydrated ion radius and a larger hydrolysis constant,but also because the calculated complexation equilibrium constant lg KSOPb was greater than lg KSOCd,indicating that the complex formed by Pb on the yellow soil surface was more stable than that formed by Cd.The correlation analysis indicated that Hs in yellow soil was primarily influenced by iron-aluminum oxides and organic matter.pH had a significant impact on pHpzc and lg KSOCd,as well as lg KSOPb in yellow soil.[Conclusion]The 1-site/2-p Ka SCM is highly applicable for accurately describing the adsorption characteristics of Pb and Cd on the surface of basalt parent yellow soil in Guizhou Province and explaining the adsorption mechanisms of Pb and Cd,.It could provide reference for the study of the migration and transformation of heavy metals in agricultural soil.

Cadmium (Cd) exposure risks to consumers of locally grown rice are often estimated without considering the sources and bioavailability of Cd. Here, we present the first comprehensive and quantitative analysis on the sources and transport of Cd in paddy ecosystems by combining a regional investigation in southern China, a positive matrix factorization algorithm, and a classification and regression tree approach. Results showed that local atmospheric emission regulations failed to mitigate Cd contamination as the Cd inputs from industrial effluent irrigation were largely overlooked. Leaching loss of soil Mn is an invisible threat to grain safety as Mn can exhibit a significant facilitation effect on rice Cd uptake under acidic pH. A probability-based toxicokinetic model is proposed to optimize the strategies for minimizing the Cd body burden through the source-soil-rice -human pathway. Urinary Cd exceeded its safety threshold in 61.7 % of local female adults (6.14 +/- 4.42 mu g g(-1) creatinine) who consumed less rice grain but with a low Zn bioavailability. To protect 85 % of local rice production from causing excessive Cd exposure risk, irrigation channel needs to be effectively cleaned up, and the pH and amorphous Mn content of rice soils need to be raised to 5.50 and 179 mg kg(-1), respectively.

When rice soils are contaminated by cadmium (Cd), the sources and timing of such contaminations need to be identified. In this study, we aimed to quantify the sources, history, and fate of Cd in the rice soils of southern China, by combining a near 10-year regional investigation, by developing a normalized positive matrix factorization algorithm, a Cd mass balance model, and probabilistic simulation. We simulated the historical contamination process of Cd in rice soils from 1991 to 2019 and the future changes from 2019 to 2069 under varying input parameters, as affected by different environmental management measures. Over the period of 1991-2019, the input flux of Cd through atmospheric deposition was estimated at 421 g ha-1, which contributed 52.1% of the total increments in soil Cd concentration. Over the next decade, a 25.6% probability is predicted that the Cd concentration of local rice soils would increase from the baseline to the upper level of soil threshold, despite the efforts of environmental regulators. Removing the rice straw from production fields, cleaning up the irrigation channels, and strengthening environmental regulations would take approximately 50 years (2019-2069) to ensure that 90% of soils were safe for rice cultivation.

The present study evaluates the sustainability of tobacco-rice rotation by reducing the phytoavailability of cadmium (Cd) to rice by combining large-scale field sampling and regional investigations in southern China. The rotation involves frequent tillage and liberal application of nitrogen and phosphorus fertilizers, which increases yields but lowers soil pH. As a result, manganese is lost from soil and, at the same time, more soil Cd is taken up by rice and tobacco. The tendency to overcompensate for the Mn loss is influenced by soil properties, crop type, and economics of cultivation. Based on the scenario analysis, this tendency and the Cd uptake risks were estimated. Dietary intake of 83.3% of rice grain produced on the rotation fields would have adverse health effects on local male nonsmokers. Besides the rice, Cd in local tobacco leaf may lead to an increase in the kidney Cd levels of local male smokers (21.5 cigarettes per day) by 16.2-fold at age 50. Field trials and model estimations indicated that for a Cd concentration below 0.2 mg dry weight kg(-1) in rice grain, the critical pH value in rice soils was similar to 6.0, and that for amorphous Mn oxide at pH 4.5-6.0 was 120 mg kg(-1).

[目的]为研究岷江上游人工植被恢复下土壤养分及土壤质量状况.[方法]本研究以人工植被恢复措施5年后的高石砾弃渣边坡、原生植被自然边坡、高石砾弃渣场边坡为对象,测定了土壤容重、pH、饱和水含量、毛细管孔隙度、总孔隙度、有机碳、全氮、全磷、速效钾和有效磷含量等理化指标,分析了土壤化学计量特征,采用土壤质量综合指数法对土壤质量进行了评价.[结果]①人工植被恢复弃渣场土壤容重显著低于弃渣场边坡,土壤理化指标(土壤饱和水含量、毛细管孔隙度、总孔隙度、有机质含量、总氮含量、全磷含量、速效钾含量和有效磷含量)显著高于原生植被自然边坡和弃渣场边坡,说明人工植被恢复改善了土壤结构,提高了土壤养分含量.②人工植被恢复弃渣场土壤N∶P和C∶P显著高于弃渣场,土壤化学计量比处理平衡状态,不受C和P的限制.③土壤综合指数为植被恢复的弃渣坡面＞原生植被坡面＞弃渣场.[结论]表明人工植被恢复能改善土壤质量,在高石砾弃渣边坡治理土壤环境的改善中发挥了积极作用.

Limestone shows great potential to reduce the production of cadmium (Cd)-contaminated rice in acidic paddy soils, but has generated uncertainty effects. We conducted batch sorption and greenhouse experiments to investigate optimal conditions of pH and amorphous manganese content (M-nox) in limestone treated-soil for suppressing the Cd uptake by rice plants. The adsorption/desorption behavior of Cd in a soil/limestone mixture was dominated by the composition and density of sorption sites, followed by sorption conditions, which were mainly influenced by soil pH and exchangeable Ca2+. Interactions among soil factors were influenced both by the limestone effects and plant responses. The Cd uptake of rice plants did not matched to the doses of limestone applied. The increase in pH and decrease in M-nox following higher dosages of limestone treatment might produce contradictory effects on rice Cd uptake. We proposed a trade-off model to demonstrate how did the interactions of soil pH and M-nox affect the rice Cd uptake. To minimize the accumulation of Cd in rice grain harvested from acidic paddy soils, limestone was applied at 0.25 % to achieve an optimal pH of 6.5 and a Mnox of 95 mg kg(-1).

Characterizing the interactions between Cd and Zn with respect to the soil soluble Cd and crop Cd uptake allows the development of risk-based approaches to the performance of grain crops. By means of a three-year survey of 358 rice fields and 206 wheat fields across China, this study investigated the effect of Cd-Zn interactions on the phytoavailability of Cd to rice and wheat. The interactive nature between the Cd:Zn ratio and pH of soil affected crop Cd uptake, and the resulting grain Cd intake risk, were examined by the Free-Ion Activity-based model and probability analysis. In highly acidic rice soils (pH < 5.9), soil Zn had no effect on rice Cd uptake, whereas, under near-neutral conditions (pH > 5.9), a site-specific influence of soil Zn on grain Cd concentration was found. Soil Zn could inhibit Cd uptake and translocation by the plant in soil-wheat system when the soil Cd:Zn ratio decreased to 0.0083 and lower. Rice grain poses a significant health risk to local consumers due to its high Cd accumulation and its low Zn accumulation. In order to reduce the health risks from dietary Cd to local consumers, approximately 63.9% of the rice fields and 30.5% of the wheat fields require strategies ameliorating soil acidity in rice soils and increasing Zn concentrations in wheat soils.

The contamination of heavy metals in upland field due to lead and zinc smelting is of great concern. In this study, a regional survey in the wheat field across the eastern plain of Jiyuan city, Northern China, was conducted to investigate the characteristics of heavy metals in soils and wheat grains. Based on the enrichment factor, potential ecological risk factor, the health risk assessment and Monte Carlo simulation method, the ecological risk of heavy metals in soil and the dietary Cd and Pb intake to consumers of locally harvested wheat grain were evaluated. Results showed that the concentrations of Cd, Pb, Cu, and Zn in soil average 1.51, 97.1, 29.0 and 79.5 mg·kg-1, respectively, which were significantly higher than their respective background values in Henan province. The concentrations of Cd and Pb in soils exceeded the national standard values by 74.2% and 10.8%, respectively. And the concentrations of Cd and Pb in wheat grain exceeded the national food safety limit standard values by 61.3% and 40.9%, respectively. Enrichment factors of heavy metals showed that the soil was extremely enriched in Cd. The high⁃risk areas were mainly distributed in the industrial areas in the southwest, northwest and mid⁃east regions, which are dominated by lead and zinc smelting. Health risk assessment results showed that the probability of non⁃ carcinogenic risk and carcinogenic risk of Cd in wheat was higher than the international recommended safety value by 27.5% and 100%, respectively. The accumulation of Cd and Pb in the wheat field of Jiyuan City is significant, which needs to be paid enough attention by the relevant departments. The combination of spatial analysis and risk assessment provides an effective risk⁃based approach for safer crop practices.

Adding limestone into acidic paddy soils might reduce cadmium (Cd) accumulation in rice plants and the harvested grains but with inconsistent results in the field practice. We conducted three experiments of different field scales, including small-plots, multi-location trial, and large-scale field samplings of rice grown in a major production region of southern China, to investigate whether liming could sustainably limit the Cd phytoavailability to rice. Forty-eight physical, chemical, and biological attributes associated with paired soils and plants were collectively analyzed. Rice Cd uptake was significantly reduced when moderate dosage (2.25-3 tha(-1)) of liming was present in the soils. The limes decreased rice Cd uptake by reducing the Cd concentrations of soil solution phase and regulating Ca2+ and Cd2+ competitions for absorption sites at root surfaces. Soil Zn hardly any effect on rice Cd uptake. Rice Cd uptake was suppressed at the higher rates of liming (4.5-9 t ha(-1)) due to the heavy loss of soil labile Mn. The tendencies of over compensating were soil-, plant-, and climate-dependent and were estimated by a transfer function and the risks were characterized using probabilistic analysis. The sustainable doses of limestone that reduced grain Cd accumulation, but did not compromise yield, or disrupt the rice rhizosphere was 3 t ha(-1) annually incorporated two weeks before the seedlings were transplanted. (C) 2019 Elsevier B.V. All rights reserved.

矿业活动对土壤系统良性运转带来较大的环境负荷,矿区周边土壤重金属污染风险评估是土壤污染防治和资源可持续开发的关键.在应用单因子污染指数法、潜在生态风险指数法、风险评价编码法(RAC),并结合空间分析和冗余分析手段的基础上,对新疆某矿冶区周边土壤重金属生物有效性和生态风险进行了系统研究.结果 表明:研究区土壤As、Cu、Mn和Cd超标率分别为88％、38％、49％和24％;土壤Mn、Zn、As和Cd弱酸可溶态高值区主要集中在尾砂库和收砷房的附近区域.单因子污染指数评价揭示As和Cu污染累积较为严重.潜在生态风险评价显示,As、Cd和Cu生态风险较高,Mn为低生态风险.风险编码法(RAC)评价结果进一步揭示Mn和Cd具有显著的土壤迁移风险.冗余分析结果显示,空间异质性是影响土壤重金属弱酸可溶态含量变异的主要因素.土壤pH和重金属弱酸可溶态是影响潜在生态风险指数(RI)的2个重要因素.综合风险评价手段与多尺度分析方法的联合应用有助于提高区域风险评价的准确性.

Very little has been reported on the effects of pH, Zn, and Mn on Cd uptake in rice ( L.) and their levels under field conditions. Rice accumulates a high concentration of Cd in acid soils, even at low soil Cd levels. Lime (CaO) was spread at 1200 kg ha on the topsoil of a rice field during the tillering stage. Effects of liming on rice Cd, soil pH, and amorphous Mn (MnO-AM) were then investigated. Slight increases in pH from 5.17 to 5.45 and MnO-AM from 66.3 to 82.1 mg kg were observed after liming. The proportion of rice samples with a Cd concentration greater than the Chinese rice Cd standard (0.2 mg kg dry wt. in grain) decreased by ∼15%. The pH, which varied from 4.8 to 5.8, did not significantly affect rice Cd, whereas soil Cd and Zn had a significantly positive effect, together accounting for ∼14% of the variance. Soil Mn had significantly negative effects on rice Cd, accounting for >18% of the variance. For a Cd concentration <0.2 mg kg dry wt. in rice grain, the critical pH value in paddy soil was ∼5.7, and that for Mn at pH 4.8 to 5.8 was ∼300 mg kg. Our findings showed that Cd concentration in rice grain in an acid paddy soil increased with an increase of Zn and a decrease of Mn when these metals were at sufficient levels.

Plant uptake factors (PUFs) are of great importance in human cadmium (Cd) exposure risk assessment while it has been often treated in a generic way. We collected 1077 pairs of vegetable-soil samples from production fields to characterize Cd PUFs and demonstrated their utility in assessing Cd exposure risks to consumers of locally grown vegetables. The Cd PUFs varied with plant species and pH and organic matter content of soils. Once normalized PUFs against soil parameters, the PUFs distributions were log-normal in nature. In this manner, the PUFs were represented by definable probability distributions instead of a deterministic figure. The Cd exposure risks were then assessed using the normalized PUF based on the Monte Carlo simulation algorithm. Factors affecting the extent of Cd exposures were isolated through sensitivity analyses. Normalized PUF would illustrate the outcomes for uncontaminated and slightly contaminated soils. Among the vegetables, lettuce was potentially hazardous for residents due to its high Cd accumulation but low Zn concentration. To protect 95% of the lettuce production from causing excessive Cd exposure risks, pH of soils needed to be 5.9 and above.

The agricultural soil in China has been widely polluted by heavy metals and the regional contamination is serious. The experience on soil remediation in developed countries is significantly instructive for farmland protection in China. The heavy metal pollution of farmlands in China faces great challenges including spatial heterogeneity of heavy metal accumulation, various enrichment characteristics depending on soil types and crop, soil acidification, loss of soil trace elements, unreasonable development patterns, significant input of heavy metal into soil, poor correlation between the heavy metal concentration in soil and crop plants, inadvisable remediation techniques, and lack of long-term risk control measures. Responses to these problems, we proposed a soil prevention and control system to promote the remediation of contaminated cropland in China, which mainly focused on pollution prevention, and take prior protection as well as risk control as basic course. Based on this system, the soil pollution prevention and control work can be implemented through systematically procedures including soil environment investigation, pollution source control, risk assessment and classification management, and the derivation of soil quality threshold.

Solid-solution partitioning coefficient (Kd) and plant uptake factor (PUF) largely determine the solubility and mobility of soil Cd to food crops. A four-year regional investigation was conducted in contaminated vegetable and paddy fields of southern China to quantify the variability in Kd and PUF. The distributions of Kd and PUF characterizing transfers of Cd from soil to vegetable and rice are probabilistic in nature. Dynamics in soil pH and soil Zn greatly affected the variations of Kd. In addition to soil pH, soil organic matter had a major influence on PUF variations in vegetables. Heavy leaching of soil Mn caused a higher Cd accumulation in rice grain. Dietary ingestion of 85.5% of the locally produced vegetable and rice would have adverse health risks, with rice consumption contributing 97.2% of the risk. A probabilistic risk analysis based on derived transfer function reveals the amorphous Mn oxide content exerts a major influence on Cd accumulation in rice in pH conditions below 5.5. Risk estimation and field experiments show that to limit the Cd concentration in rice grains, soil management strategies should include improving the pH and soil Mn concentration to around 6.0 and 345 mg kg-1, respectively. Our work illustrates that re-establishing a balance in trace elements in soils' labile pool provides an effective risk-based approach for safer crop practices.

Vegetable crop consumption is one of the main sources of dietary exposure to toxic trace elements (TEs). A paired survey of soil and vegetable samples was conducted in 589 agricultural sites in the Youxian prefecture, southern China, to investigate the effect of soil factors on the accumulation of arsenic, cadmium, mercury, and lead in different vegetables. A site-specific model was developed to estimate the health risk from vegetable consumption. The TE concentration varied in different plant species, and rape can be cultivated in contaminated areas for its potential use in restricting the transfer of TE from soil to edible plant parts. The accumulation of TEs in vegetables was governed by multiple factors, mainly element interaction, metal availability (extractable CaCl2 fraction), and soil pH. Soil Zn may promote Cd accumulation in vegetables when soil Cd/Zn ratio>0.02. Cadmium is a major hazardous component. About 80.8% of the adult populations consuming locally produced vegetables had a daily Cd intake risk above the safe standard. Among investigated vegetables, radish is potentially hazardous for populations because of its high consumption rate and high Cd content but low Zn accumulation. The consumption of radish cultivated in highly acidic soil (4<pH≤5) and high Cd contamination (CaCl2-Cd=1.0mgkg-1) had a significant probability (89.4%) to be above the safe standard; while this risk was significantly decreased to 8.9% in soil of near-neutral pH (6<pH≤7). The wide range of TE concentrations and soil factors suggests that a site-specific risk assessment is needed for better and safer vegetable production.

The high level Cd concentration in rice in the Youxian Prefecture has been recognized as a health hazard.Based on the path analysis (PA) model,multi-statistical method and K-means cluster method,this study investigated the enrichment characteristics of Cd in the soil-rice system,potential ecological risk and major influcnce factor.Results showed that significant enrichment of Cd in soil-rice system was found throughout the Youxian prefecture.The concentration of Cd in rice was 0.47 mg·kg-1,2.5 fold higher than the national limits.The plant uptake factor (PUF) followed well with the natural lognormal distribution.The regression and PA analysis showed that soil pH,soil Mn and soil Zn were three main factors contributing to the variability of PUF.Soil Mn was the major factor influencing rice Cd uptake.The good correlation between PUF and soil pH and soil Zn are connected to the influences of these two variables on soil Cd concentration.K-means cluster analysis showed that soil pH =5.6 and soil Mn =333 mg· kg-1 could be taken as the initial regulation standard for Cd pollution control in the study area.

A regional investigation in the Youxian prefecture, southern China, was conducted to analyze the impact of environmental factors including soil properties and irrigation in conjunction with the use of fertilizers on the accumulation of Cd in vegetables. The Cd transfer potential from soil to vegetable was provided by the plant uptake factor (PUF), which varied by three orders of magnitude and was described by a Gaussian distribution model. The soil pH, content of soil organic matter (SOM), concentrations of Zn in the soil, pH of irrigation water and nitrogenous fertilizers contributed significantly to the PUF variations. A path model analysis, however, revealed the principal control of the PUF values resulted from the soil pH, soil Zn concentrations and SOM. Transfer functions were developed using the total soil Cd concentrations, soil pH, and SOM. They explained 56% of the variance for all samples irrespective of the vegetable genotypes. The transfer functions predicted the probability of exceeding China food safety standard concentrations for Cd in four major consumable vegetables under different soil conditions. Poor production practices in the study area involved usage of soil with pH values <= 5.5, especially for the cultivation of Raphanus sativus L, even with soil Cd concentrations below the China soil quality standard. We found the soil standard Cd concentrations for cultivating vegetables was not strict enough for strongly acidic (pH <= 5.5) and SOM-poor (SOM <= 10 g kg(-1)) soils present in southern China. It is thus necessary to address the effect of environmental variables to generate a suitable Cd threshold for cultivated soils. (C) 2016 Elsevier Ltd. All rights reserved.