Freeze-thaw Effect On The Characteristics Of Perennial Ryegrass Germination Seeding And Growth In The Soil Polluted By Heavy Metals

Freezing and thawing actions is the biotic stress acting on the soil (Marumoto etal.,1982),the phenomenon of Water-ice Phase Changes and its accompanyingphenomenon would complicate the unstable soil and water system. The changeswould have significant influence on the soil properties and the chemical speciation ofheavy metals, plant seeds germination and seeding growth, plants on the absorption，enrichment and migration ability of element, moreover, impact the quality andbiomass of the plants. Seasonal freeze-thaw is the main climate characteristics of theBlack soil area in North-east China. On the background of the severe changes inglobal climate, The great theoretical and practical significance of the development ofthe research is to reveal the plant seed germination in the freeze-thaw period and themigration transformation rules of the heavy metals in the Soil-Plant system, guide thecrop cultivation and control of the soil pollution from the heavy metal.Investigated by laboratory simulation method，we study the characteristics ofperennial ryegrass germination Under the action of freeze-thaw，seeding growthcharacteristics、heavy metal distribution in the body of perennial ryegrass、andenrichment and migration ability to the of heavy metals by ryegrass. Besides， weresearch on the influence on the process mentioned above and the effect in differentthawing situation, as freeze-thaw frequency、soil moisture content and freezingtemperature. Meanwhile, compared by the non-freezing and thawing situation, wecould analyze the preliminary reason of it. Conclude that in the Freeze-thaw situation,adding the outer organic matter could greatly influence the the characteristics ofperennial ryegrass germination, seeding growth characteristics）、 heavy metaldistribution in the body of perennial ryegrass, ryegrass on the enrichment andmigration ability of heavy metals element in the soil pollution from the heavy metal.DOM is one key element influencing the phenomenon and process above. Accordingto the analysis and the situation above, my dissertation is a research on the DOMenvironmental behavior in the freeze-thaw cycle and could conclude as followed:The freezing and thawing actions influence the characteristics of perennial ryegrass germination and related to the heavy metal properties. In the soil polluted byPb, the freezing and thawing actions increase the germination rate and index ofryegrass, as long as the inhibitory effect by Cd，Compared by the blanked soilpolluted by the heavy metal, Adding the straw increase the germination rate, thegermination index and potential, contrary to adding the sludge. Thawing situation isalso the key element influenced by the characteristics of perennial ryegrassgermination. which lead by the freeze-thawing actions As the mutual effect andrelation of soil properties and heavy metal form cover the influence by chemical formof heavy metal to the characteristics of perennial ryegrass germination rate, some soilproperties such as DOM, Ph, Eh could be the key element influencing the perennialryegrass germination characteristics. In addition, the freeze-thawing actions arose thedetail changes between soil properties and the perennial ryegrass germinationcharacteristics parameters.The freeze-thawing actions prompt the growth of the dry weight of root, stem andthe root length and the stem length, decrease the root-shoot ratio, But the changeinfluenced much by Pb and Cd properties. Freeze-thaw frequency、soil moisturecontent and freezing temperature could influence the perennial ryegrass seedinggrowth, which differs by the changes of the Pb and Cd properties. The reason of thephenomenon above is that the freeze-thawing actions influence much the soilproperties and the heavy metal chemical situation, which influence more complicat-edly to the characteristics of the perennial ryegrass seeding growth.DOM, is the keyparameter, Ec、CEC、CaCO3、Microbial amount of carbon, Cellulose enzyme activityis the key parameters influence the perennial ryegrass seeding growth, soil aggregateis the in dependent parameter. After the freeze-thawing, the heavy metal propertieschanges in the soil, therefore, the influence to the perennial ryegrass seeding growthchanges.The distribution of the heavy metal in the body of the perennial ryegrass isinfluenced by the freeze-thawing action，which decrease the content of the heavymetal in the plants stem, increasing the content of Cd in the body and the root.Compared by the blanket soil polluted by the heavy soil, Adding the straw and increase the dry weight of root and the root length, adding the sewage sludge decreasethe dry weight of root and the root length. Thawing situation is also the key elementinfluenced by the heavy metal distribution in the body of the perennial ryegrass. Thereason of the phenomenon above is freeze-thawing actions have significant influenceto the soil properties and the chemical speciation of heavy metals. After thefreeze-thawing, the properties and the chemical speciation of the soil polluted byheavy metal influence more complicatedly. Not only change the relation between theinfluential element and the parameters of the perennial ryegrass seeding growth,which turns out to be the key element impacting the characteristics. Some soilproperties and the form of the heavy metal differs much in the means of thedistribution of the heavy metal in the body of the perennial ryegrass and therelativities of the enrichment and migration ability of heavy metals element beforeand after the freeze-thawing action.In the range of the balance concentration in the dissertation, in most of the cases,DOM can not be absorbed and contrarily prompt the desorption release of the blacksoil organic matter. Freeze-thawing action increase the desorption release by theDOM to the black soil organic matter and increase the desorption release system pHand Ec. The effect of DOM to the black soil organic matter increase as the increasingof the pH value and the decrease of the lonic strength. Freezing conditions is the keyelement effecting the absorption of the DOM by the soil. DOM obtained by differentfreeze-thawing condition has the desorption release role and the role perform thesimilar laws as the change of the freezing temperature and the change of the moisturecontent.The degradation of the DOM in the straw and sewage sludge can be sorted asquick and slow phase, which conform to the Level one Reaction kinetics equation.Compared by the non-freeze thawing action, freezing thawing action decrease thedegradation rate and velocity, accompany by the decrease of the Ph and the Ec, theincrease of the large molecules and hydrophobic components, which affect greatly bythe lonic strength and the lon type. In the neutral condition, the constant of thedegradation rate in the straw and sewage sludge reaches maximum, and the half-life period reaches minimum. Although in the same degrade period, the rate of the degradeof the sewage sludge differs from the lonic strength, the relation between the lonicstrength, the constant of DOM degrade rate and the half-life period. Compared by theDOM degrade of the sewage sludge, except that the lonic type NaNO3,the degrade ofthe straw DOM needs much longer. The influence of the straw and the sewage sludgeby freeze-thaw frequency、soil moisture content and freezing temperature showscomplicity and validity, which related much to the great diversity by composition andthe nature of the DOM released by the straw and the sewage sludge in differentfreeze-thawing situation.