تغييرات اجزاء و قابليت زيست فراهمي فلزات سنگين در ريزوسفر ذرت و آفتابگردان رشد يافته در يك خاك آلوده

چكيده انگليسي :

Changes of Heavy Metal Fractions and Bioavailability in the Rhizosphere of Zea mays and Helianthus annuus Grown in a Contaminated Soil Ali Asghar Moradian Ali moradian13@gmail com Data of Submission March 12 2011 Department of Soil Science Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiM Shirvani Assist Prof Supervisor H Shariatmadari Prof Supervisor Abstract In order to evaluate the risks of heavy metals contamination it is essential to understand theirbioavailability which depends on their form in the soil rather than on the total amount accumulated The conditionsat the root soil interface often referred to as the rhizosphere are considerably different from those existing somedistance from the root system On the other hand the complexity of the soil plant relationship may induce changesin the properties of the soil rhizosphere and consequentially the metal fractionation in it Studies dealing with plant induced changes in heavy metals fractionation in the rhizosphere soil sometimes produce different results However temporal changes in metal fractionation during plant growth may provide another reasonable explanation Theprimary objective of this study was to investigate Zn Pb Cu Ni Cr and Co fractionation in the soil in an attempt toobtain a better understanding of their availability and subsequent uptake by maize and sunflower In this regard thestudy focused on root induced changes of various fractions of Zn Pb Cu Ni Cr and Co in the maize and sunflowerrhizosphere Plants were seeded in a rhizobox a box that is consisted of four parts constructed from polyvinylchloride mesh The devices were cultivated for 21 42 and 63 days for maize and sunflower and 84 days only formaize At the termination of the cultivation period maize and sunflower plants were harvested and soil sampleswere collected For fractionation of heavy metals the soil samples were sequentially extracted using anoperationally defined sequential fractionation procedure The total organic carbon TOC in the soil and the DOC inthe soil solution were determined using a TOC analyzer The results demonstrated that there were continuouschanges in heavy metals fractionation within the maize and sunflower rhizosphere Initially the amount ofexchangeable fraction increased before dropping below the initial level after 42 days or so The exchangeablefraction of Cu and Zn in the soil rhizosphere did not further increase after 21 days While the exchangable fractionof Ni further increased after 63 days Carbonate associated Zn Cu and Ni followed a similar trend of change butwith a slower rate than the exchangeable fractions There were also initial increases in oxide bound copper followedby a turnover after 40 50 days but in the case of Zn from the beginning until the end of planting this fractionshowed continuous increase Metal fraction bound to organic mater for most metals studied increased significantlyat the 63 days after planting Changes in the organic fraction in distance from both plant s root for the most ofheavy metals in study was significant and the rhizosphere and bulk soil have maximum and minimum concentrationof organic fraction respectively Unlike the organic matter bound fraction residual form showed its highest andlowest concentration in the rhizosphere and bulk soil respectively The amount of accumulated heavy metalabsorbed in the plant material exceeded the initial quantity of the exchangeable fraction in the soil revealing atransformation from less bioavailable to more bioavailable fractions During the plant growth increases in pH anddissolved organic carbon DOC were measured in the maize and sunflower rhizosphere which might considerablyaffect the metal forms in this studyKey words Bioavailability Fractionation Heavy Metal Rhizobox Rhizosphere SequentialExtraction Procedure

مراديان، علي اصغر

تغييرات اجزاء و قابليت زيست فراهمي فلزات سنگين در ريزوسفر ذرت و آفتابگردان رشد يافته در يك خاك آلوده

جزء بندي , رايزوباكس , ريزوسفر , عصاره گيري متوالي , قابليت زيست فراهمي