| Tall fescue has a certain potential for heavy metal pollution,and rapid growth and resistance to cutting.In order to investigate the effects of different cutting frequency(no cutting,once,twice,5 times)on lead(Pb)and cadmium(Cd)accumulation in tall fescue and the changes of Cd and Pb form,two cutting tests under Cd and Pb stress were carried out in hydroponic and soil culture.The hydroponics experiment investigated that under Cd and Pb toxicity stress,the effect of cutting on the relationship between biomass of different parts in tall fescue and Cd,Pb accumulation.And observed the distribution of heavy metals and the morphological changes of subcellular cells in mature leaves and root tip cells.The soil culture pot test explored the effect of cutting on soil acid environment and Cd,Pb form,and the subcellular morphological changes and heavy metal distribution,and the correlation between the diversification of Cd,Pb morphological transformation and Cd,Pb accumulation of different parts in tall fescue.The main results are as follows:1)With the increase of cutting frequency,the biomass of cutting parts,stubble and root in tall fescue showed a decreasing trend,under 5 times cutting,the effect on root biomass was the largest,and the decrease rate was more than 50%.In opposition the content of Cd and Pb in the stubbie and root of tall fescue increased,the average increase of Cd and Pb content in the stubble was between 32%and 61%,and in roots was between 65%and 83%,which showed the cutting promoted the absorption of Cd and Pb by root and transport to the stubble.The Cd and Pb transport coefficients showed a decreasing trend with the increase of cutting frequency.The aboveground Cd and Pb accumulated mainly in the stubble,and The accumulation of Cd and Pb in stubble accounted for 50%-60%of aboveground total accumulation,due to the short time interval of 5 cutting treatments,the accumulation of Cd and Pb and the aboveground accumulation of tall fescue were significantly decreased.2)Due to the large amount of Cd and Pb absorbed by the cutting process and the transport to the stubble,compared with the same concentration of Cd,Pb treatment,under Cd,Pb+cutting treatment the chloroplast of the stubble mature leaves was spherical,and a large number of plastids were found in the matrix.The structure of the thylakoid membrane was loose and not clear.Root nuclei in the nuclear membrane is not clear,vacuoles and cell walls gathered a large number of Cd,Pb dense electron particles,and even the phenomenon of wall separation.3)Under soil pot experiment,cutting treatment increased the acidity of soil,the acid-extractable and reducible state of Cd and Pb in soil showed an increasing trend,and the acid-extractable and reducible state contents with 5 times cutting were significantly higher than those of other cutting treatments.When Cd 50 mg/kg and Pb 1500 mg/kg were added,the contents of Cd and Pb acid-extractable were 30%-40%of the total amount of heavy metals,the contents of Cd and Pb reducible were about 40%.Therefore,the cutting treatment has improved the bioavailability of Cd and Pb in the soil.4)In this study,the Cd and Pb contents in the stubble and root of tall fescue were significantly positively correlated with the acid-extractable and reducible state contents of Cd and Pb in the soil,and the correlation coefficients were above 0.8,indicating that the increase of acid-extractable and reducible state contents of Cd and Pb is beneficial to the uptake of Cd and Pb in tall fescue. |
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