Studies on Heavy Metal Pollution in Soil-Plant System:A Review

Heavy metal pollution in soil-plant system is of major environmental concern on a world scale and in China in particular with the rapid development of industry. The heavy metal pollution status in soil-plant system in China, the research progress on the bioavailability of heavy metals (affecting factors, extraction methods, free-ion activity model, adsorption model, multivariate regression model, Q-I relationship, and compound pollution), and soil remediation are reviewed in the paper. Future research and monitoring is also discussed.

Comparison of Urea-Derived N_2O Emission from Soil and Soil-Plant System

A pot experiment with a sandy loam soil and spring wheat as test crop was conducted to compare the N2O emission from soil system with plant cut off and from soil-plant system with plant kept. The results showed that after urea fertilizer applied, the N2O emission from soil and soil-wheat system decreased exponentially with time, and its total amount was 0.34%~0.63% and 0.33%~0.58% of applied urea-N respectively, no significant difference being found between these two systems. The N2O emission had a very significant negative relationship (P = 0.01) with the biomass of wheat plant. A combined application of urease inhibitor hydroquinone and nitrification inhibitor dicyandiamide could reduce the N2O emission by 50%~83% and 46%~74%, respectivelyl from soil and soil-wheat system. The N2O was mainly produced and emitted from soil, and the soil biochemical regulation, i.e., applying related inhibitors into soil could effectively diminish the urea derived N2O emission.

Distribution of Crystal Organic Fertilizer-N in Soil-plant System

The distribution of crystal organic fertilizer, urea and compound fertilizer-N in soil and plant system was researched with 15N-trace under tobacco pot experiment. The results showed that the leaf yield of tobacco used crystal organic fertilizer was 23.1% and 14.6% higher than that of urea and compound fertilizer treatments respectively. Compound fertilizer also resulted in higher yield of 8.5 % comparing with the urea treatment. Nitrogen content of the plant from the crystal organic fertilizer treatment was 138. 6% and 145.7% as high as that of the compound fertilizer and urea treatments respectively. The absorbed N from the organic fertilizer was 25.1% and 27.9% more than that from the compound fertilizer and urea respectively. However, the absorbed N from the soil with the organic fertilizer was 47.4% and 58.3% more than that with compound fertilizer and urea respectively. The N use efficiency of the organic fertilizer was 9.4% and 10.1% higher than that of the compound fertilizer and urea. It indicated that the crystal organic fertilizer not only had high N use efficiency, but also stimulated tobacco taking up more N from soil.

Diversity of endophytes across the soil-plant continuum for Atriplex spp. in arid environments

Endophytes are hypothesized to be transferred across the soil-plant continuum, suggesting both the transfers of endophytes from environment to plant and from plant to soil. To verify this hypothesis and to assess the role of locality, we evaluated the similarity of microbial communities commonly found both in soils and endophytic communities in three arid regions, i.e. the Jornada LTER （Long Term Ecological Research） site in New Mexico, USA, and the research station of Jordan University of Science and Technology （JUST） and Khanasd research station in Badia region of Jordan. Rhizosphere and non-rhizosphere soils, leaves and seeds of Atriplex spp. were sampled. Diversity and distribution of bacteria and fungi across the soil-plant continuums were assessed by tag-encoded FLX amplicon pyrosequencing and sequence alignment. Of the total bacterial OTUs （operational taxonomic units）, 0.17% in Khanasri research station, 0.16% in research station of JUST, and 0.42% in Jornada LTER site were commonly found across all the plant and soil compartments. The same was true for fungi in two regions, i.e. 1.56% in research station of JUST and 0.86% in Jornada LTER site. However, in Khanasri research station, 12.08% of total fungi OTUs were found in at least one soil compartment and one plant compartment. Putative Arthrobacter, Sporosarcina, Cladosporium and members of Proteobacteria and Actinobacteria were found across all the soil-plant continuums. Ascomycota, mainly including Didymellaceae, Pleosporaceae and Davidiellaceae were present across all the soil-plant continuums. Microbial communities in two regions of Jordan were similar to each other, but both of them were different from the Jornada LTER site of USA. SIMPER （similarity percentage） analysis of bacterial and fungal taxa for both soil and endophyte communities revealed that dissimilarities of two bacterial genera （Arthrobacter and Sporosarcina） and two fungal genera （Cladosporium and Alternaria） are very high, so they play key roles in the soil-plant continuums. A weighed Pearson correlation analysis for the specific bacterial OTUs in the soil-plant continuums only showed high similarity between the two regions of Jordan. However, fungal groups showed higher similarities among all regions. This research supports the hypothesis of continuity of certain bacterial and fungal communities across the soil-plant continuums, and also explores the influences of plant species and geographic specificity on diversity and distribution of bacteria and fungi.

Effects of soil-plant system change on ecohydrology during revegetation for mobile dune stabilization, Chinese arid desert

Soil-plant systems play an important role in sand fixing and surface protection in the arid desert of China. This study examines the ecohydrological responses after a soil-plant system change for mobile dune stabilization by using a series of soil hydrological experiments and ecological investigation. The study results showed that decades of succession of soil-plant system has endangered the stability of the protection system. With the accumulated water and nutrient, a bio-logical system develops in a thinner and thinner surface soil. Redistribution of precipitation has changed completely in the ecosystem. In 3–15 mm of soil, a high capacity of crust water retention ultimately limits most rainfall from infiltrating below 10–20 cm deep. When that takes place, lower plants begin to compete for water with grasses and shrubs. A drought horizon forms in 20–500 cm depth with shrub transpiration. Artificial shrubs with deep roots obtain hardly rainfall supply and are gradually eliminated from the protection system. All changes in water environment affect the structure and func-tion and stabilization of whole protection systems. It is necessary to establish a relatively stable water environment by managing the soil-plant system for constructing a sustainable protective system in arid desert.

Trace Elements in the Soil-Plant Systems of Copper Mine Areas-A Case Study From Murgul Copper Mine From the Black Sea Region of Turkey

This study presents a case study on the heavy metal analysis of soil and plant samples around the Murgul copper mine,one of the first and most important mining areas in Turkey.An attempt has been made to investigate the status of trace elements like Al^(3+),Fe^(2+),Cu^(2+),Zn^(2+),Pb^(2+),Ni^(2+),Co^(2+)and Cd^(2+)in soils and plants.The sampling localities were taken from 500 m,600 m,and 1000 m altitudes around the factory and at 1400 m in the forest zone.The aboveground parts and foliage ash of Silene compacta,Tussilago farfara,Smilax excelsa,Rhododendron ponticum,R.luteum,and herbal mix were analysed.The results of analysis have revealed the minimum and maximum concentrations measured in the plants as follows;aluminium(20-8985 mg kg^(-1)),cadmium(0.0-0.5 mg kg^(-1)),cobalt(0.0-5.5 mg kg^(-1)),copper(0.0-347.5 mg kg^(-1)),iron(25-9320 mg kg^(-1)),lead(2-51 mg kg^(-1)),nickel(1.5-16.5 mg kg^(-1)),and zinc(13.0-221.0 mg kg^(-1)).In the soil the concentrations of aluminium,cadmium,cobalt,copper,iron,lead,nickel,and zinc vary between 33-457,0.0-0.0,0.0-0.4,0.1-88.7,14-50,0.3-4.1,0.2-0.8,and 4.0-20.3 mg kg^(-1) respectively.These findings enlighten the fact that copper is generally toxic in the soils as well as plants.Silene compacta has been recorded as a high copper accumulator,behaving as a healthy plant on the polluted sites of the area alongside the Murgul creek(especially at 600 m).This study stresses the fact that it is imperative to assess and monitor the levels of heavy metals in the environment due to anthropogenic activities,including mining,for evaluation of human exposure and for sustainable environment.

Remediation of Arsenic Toxicity in the Soil-Plant System by Using Zinc Fertilizers

Availability of soil arsenic (As) and plant As at various levels of zinc (Zn) and As applications were examined. A pot-culture experiment with a leafy vegetable, Kalmi (Ipomoea aquatica), on an Inceptisols, was conducted where As was applied with irrigation water at the rates of 0 mg/L (As control), 0.5 mg/L, 1 mg/L and 2 mg/L and Zn was added to the soil as ZnCl2 solution at the rate of 0 mg/L (Zn control), 1 mg/L, 2 mg/L and 3 mg/L during pot preparation. The experiment was conducted in triplicates for 45 days till the plants were grown to maturity. At the end of the experiment the remedial effect of Zn on As toxicity was examined and as such, yield parameters, As and Zn accumulation in Kalmi plants, residual concentrations of As and Zn in soils and plants were measured. It appeared from the present study that there exists an antagonistic relationship between Zn and As i.e., Zn in soils was found to reduce As availability in soils as well as its accumulation in plants, particularly at an elevated application rate of 3 mg/L Zn. The findings could be used as a strategy to mitigate arsenic toxicity in As contaminated soils.

Stndy on Transfer of Ni in Soil-Plant System Using ￣(63)NiTracer Method

study was carried out on the transfer of native and added Ni towards plant both in different soils andat different time by using ￣(63)Ni tracer technique. The transfer of added Ni in soil was greater than native Niand declined as time increased. The mobility was greater for soluble plus exchangeable fraction of soil Nibut very smaller for residual and Fe/Mn oxide bound fractions. These indicated that Ni was more mobileand more harmful in soils with a low pH and/or low content of Fe/Mn oxides.

Macro and Micro Nutrient Supply to Soil and Plants from Sugar Mill Mud

The effects of sugar mill mud application on the availability of nutrients for plant uptake were investigated. Mill mud generated from conventional sugar mill operations was applied in three different rates and a leafy vegetable, locally called “PuiShak” or Indian spinach (Basellarubra L.) was grown for 60 days as a test crop in a pot culture experiment. Crop yield and essential nutrients like N, P, K and Zn uptake concentration was determined to come up with an inference that higher doses of mill mud application impose better effect on root and shoot uptake of these elements. A little infraction was observed for nitrogen uptake by plants for the maximum dose.

The Transfer of Cu, Zn, Mn and Fe between Soils and <i>Allium</i>Plants (Garlic and Onion), and Tomato in the Southwest of the Buenos Aires Province, Argentina

Chemical extraction methods are generally used to evaluate trace element concentrations in soils. The adequacy of these soil tests is commonly assessed by comparing the extraction results with the metal contents in the plants. In this study, soil and leaf samples were collected in the southwest area of the Buenos Aires Province, Argentina. Garlic (Allium sativum L.), onion (Allium cepa L.) and tomato (Solanum lycopersicum L.) are species of great regional economic importance. These crops need good mineral nutrition for optimum growth and sustainable production. Cu, Zn, Mn and Fe micronutrient uptake by plants was analyzed together with the trace element contents in the soil in which those plants were grown. A single EDTA-extraction procedure was performed to determine soil micronutrients. The amount of extractable-trace elements increased as the concentration of the chelating agent EDTA increased. The range of total element content in soil was: 15.68-31.5 mg·kg-1 for Cu, 75.0-386.3 mg·kg-1 for Zn, 542.5 -1686 mg·kg-1 for Mn and 28,325-32,675 mg·kg-1 for Fe. Micronutrient contents in mature leaf tissue were determined by the acid digestion method. Total and available micronutrient content in soil as well as total content in leaves were measured by flame atomic absorption spectrometry (FAAS). Total micronutrient content and the available extractable-fraction in soils were below the critical values for plant growth. This was in agreement with the amount of micronutrients present in the leaf tissue. A strong relationship between the extraction data and the soil-plant transfer coefficients suggested an appropriate exchange of trace elements from soils to garlic, onion and tomato plants.

Effect of a High Silver Stress on the Element Transfers from a Smectite-Type Clay Substrate to Plants

Two species of radishes, Raphanus sativus and Raphanus raphanistrum, were grown in the laboratory in the same substrate consisting of a smectite-type clay, which was watered at the beginning of the experience with 50 ml of a solution containing either none or 1000, 2000 or 4000 mg/L of AgNO3, respectively. Occurrence of the toxic metal in the substrate outlines higher element uptakes by the cultivated species Raphanus sativus than by the wild species Raphanus raphanistrum, except for the highest degree of Ag pollution. After a one-month growth in the Ag-polluted substrate, Raphanus sativus was depleted in most of the major, trace and rare-earth elements, except for Al, Fe, Th, Ag and U that increased in the radishes from substrate polluted by 2000 mg/L of AgNO3, and Sr, Co, Ni, U and Ag that increased in the radishes from substrate polluted by 4000 mg/L of AgNO3. Raphanus raphanistrum was enriched in all elements except Si, Na, Rb and K in the polluted substrate. The uptake was monitored by a cation-exchange process in the rhy-zosphere between mineral particles and the watering solution in the presence of various enzymes with specific activities that induced a variable uptake with the REEs being even fractionated. These activities most probably depend on combined factors, such as the plant species, and the chemical and physical properties of the substrate. The results obtained here reveal also that accumulation of nutrient elements and others in the plants is not uniform at a given Ag pollution of the substrate and therefore at a given Ag contamination in the same plant species.

Transfer Factor of Heavy Metals due to Mining Activities in Some Parts of Plateau State,Nigeria(Health Implications on the Inhabitants)

Accumulation of heavy metals in agricultural soils is instigated by industrial and other human activities such as mining,smelting,cement-pollution,energy and fuel production,power transmission,traffic activities,intensive agriculture,sludge dumping and melting operations.Plants received heavy metals from soils through ionic exchange,redox reactions,precipitation-dissolution,and so on,which implies that the solubility of trace elements based on factors like minerals in the soil(carbonates,oxide,hydroxide etc.),soil organic matter(humic acids,fulvic acids,polysaccharides and organic acids),soil pH,redox potential,content,nutrient balance,other trace elements concentration in soil,physical and mechanical characteristics of soil,soil temperature and humidity,and so on.In this study,the soil-edible plant and soil-water Transfer Factor(TF)for various metals showed that the TF values differed slightly between the locations.On soil-edible plant transfer,the mean TF for different heavy metals in soil-edible plants decreased in the following order:As(0.6)mg/kg>Cd(0.1)mg/kg>Cr(0.06)mg/kg>Pb(0.003)mg/kg>Ni(0.001)mg/kg.The total TF for different locations decreases in the following order:Barkin Ladi(1.0)mg/kg>Jos South and Jos East(0.7)mg/kg>Bassa and Mangu(0.6)mg/kg.On soil-water transfer,the mean TF for different heavy metals in soil-edible plants decreased in the following order:Cd(0.001)mg/L>As(0.0007)mg/L>Cr(0.0005)mg/L>Pb(0.0001)mg/L and Ni(0.0001)mg/L.The total TF for different locations decreases in the following order:Jos South(0.003)mg/kg>Barkin Ladi,Bassa,Jos East and Mangu(0.002)mg/kg.Based on the findings of this study,it can be concluded that the water and edible plants in the study area are good for public consumption,even though,regular checking of heavy metals in the study area is recommended.

Characteristics of Dried Soil Layers Under Apple Orchards of Different Ages and Their Applications in Soil Water Managements on the Loess Plateau of China

Negative soil water balance （i.e., water input 〈 water output） can lead to soil desiccation and subsequently the occurrence of a dried soil layer （DSL）. The DSLs are generally studied at a specific sampling depth （e.g., 500 cm）, and the actual extent of DSLs remains unknown due to the challenge of collecting deep soil samples. To investigate the characteristics of actual DSLs under different ages of apple orchards and ascertain the optimal age of apple orchards for avoiding/controlling the formation of DSLs, soil samples were collected to a depth of 1800 cm under apple orchards of different ages in Changwu on the Loess Plateau of China. As the ages increased, soil water content （SWC） and mean SWC in DSLs showed an overall decreasing trend, whereas while DSL thickness and the quantity of water deficit （QWD） in DSLs demonstrated an increasing trend. The DSL was the thickest （1 600 cm） under the 17-yeax-old orchard, the forming velocity of DSL thickness was the highest at the apple tree growth stage of 9-17 years （168 cm year-l）, and the highest increasing velocity of QWD （-181 mm year-1） was also observed at this stage. The thickness of DSL was significantly correlated with growth age and root depth of apple trees （r 〉 0.88）, whereas the QWD and mean SWC in DSLs were found to have no correlation with them. The optimal age of apple orchards for avoiding/controlling the formation of DSLs was about 9 years. This information provided pertinent references for the management of deep water resources by controlling the growth age of plants. Key Words： deep soil, growth age, plant roots, soil desiccation, soil water content, soil-plant water relation.

Ecohydrological change mechanism of a rainfed revegetation ecosystem at southeastern edge of Tengger desert,Northwest China

Study is made on a 45 km-long artificial ecosystem without irrigation in Tengger desert on the basis of long-term ecological monitoring and ecohydrological fundamentals.Changes in water allocation, utilization, cycle and balance patterns in more than 40-year evolution of the soil-plant system are analyzed. The formation of a drought horizon in shrub rhizosphere and its effect, ecohydrological function of the crust and its effect on the soil-plant system change are discussed. Driven by water self-regulation and water stress, the soil-plant system is going to develop towards the steppe desert to ensure more effective use and optimum collocation of water resource.

Transmission of antibiotic resistance genes in agroecosystems: an overview

The use of antibiotics in human medicine andanimal husbandry has resulted in the continuous release ofantibiotics into the environment, which imposes highselection pressure onbacteria to develop antibioticresistance. The spread and aggregation of antibioticresistance genes (ARGs) in multidrug-resistant pathogensisone of the most intractable clinical challenges.Numerous studies have been conducted to profile thepatterns of ARGS in agricultural ecosystems, as this isclosely related to human health and wellbeing. This paperprovides an overview of the transmission of ARGs inagricultural ecosystems resulting from the application ofanimal manures and other organic amendments. The futureneed to control and mitigate the spread of antibioticresistance in agricultural ecosystems is also discussed,particularly from a holistic perspective, and requiresmultiple sector efforts to translate fundamental knowledgeinto effective strategies.

Using a systems modeling approach to improve soil management and soil quality

Soils provide the structural support, water andnutrients for plants in nature and are considered to be thefoundation of agriculture production. Improving soilquality and soil health has been advocated as the goal ofsoil management toward sustainable agricultural intensifi-cation. There have been renewed efforts to define andquantify soil quality and soil health but establishing aconsensus on the key indicators remains difficult. It isargued that such difficulties are due to the former ways ofthinking in soil management which largely focus on soilproperties alone. A systems approach that treats soils as akey component of agricultural production systems ispromoted. It is argued that soil quality must be quantifiedin terms of crop productivity and impacts on ecosystemsservices that are also strongly driven by climate andmanagement interventions. A systems modeling approachcaptures the interactions among climate, soil, crops andmanagement, and their impacts on system performance,thus helping to quantify the value and quality of soils.Here, three examples are presented to demonstrate this. Inthis systems context, soil management must be an integralpart of systems management practices that also includemanaging the crops and cropping systems under specificclimatic conditions, with cognizance of future climatechange.