Studies On The Effects Of Hg Pollution In Soil On Growth Of Flue-cured Tobacco And Threshold Value Of Hg Toxicity

The effects of Mercury on Growth of Flue-cured Tobacco were experimented in Pot And Critical index of Mercury Toxicity was Studied at Henan Agricultural University and Ddmonstration Plot of Scientific Research and Teaching during 2004-2005.The results at follows:Firstly Mercury added to soil has severe impacted on Growth of Tobacco. when mercury concentration was 10 - 120mg. kg^-1 in soil,the yield of Flue-cured tobacoo was decreased 21. 04-54. 35%. Growth of the roots were restrained, the roots was short ,thin and brown in the soil. with increasing of mercury concentration in the soil,dry weightily of tobacoo stem and leaf were decreased in evidence .when mercury concentration was under 30mg. kg^-1 in the soil,the dry weightily of tobacoo was slow decreased .But when mercury concentration was above 30mg/kg in the soil, the dry weightily was rapid decreased.Secondly The effects of Mercury in soil on photosynthesis fluorescence characters were studied, results show when concentration of mercury in soil was in 10mg. kg^-1,30mg. kg^-1 the net photosynathetic rate (Pn),water utilize rate (WUE),.maximal PS II light energy transformation efficiency(Fv/Fm), PS II activity(Fv/Fo), steady fluorescence, the photochemical quenching coefficient(qP),the non-photochemical quenching coefficient(qN) and the apparent photosynthetic electron transport rate (ETR) were increased, but when concentration of mercury in soil was in 60 and 90 and 120mg. kg^-1,thery were decreased .as increasing of the concentration of Hg in soil ,stoma conductance (Cond),transpiration rate (Tr), intercellular CO₂ concentration,leaf temperature , vapor pressuer deficit,beginning fluorescence ,variable fluorescence,maximum fluorescence decreased.Thirdly the effects of mercury on physiology characters in tobacoo were studied ,the results show when the concentration of mercury concentration in soil was under 30mg. kg ^-1or30mg. kg^-1 ,the content of chlorophyll decreased. but when the concentration of mercury in soil was above 30mg/kg, the content of chlorophyll increased, with the increasing of mercury in soil, the chlorophyll a/b decreased and the changes of carotenoid content do not present evidence rule . watery mecury(10and30mg. kg^-1) can improve activity of SOD and POD in tobacco leaf as well activity of roots, thick mecury (60 and 90 and 120mg. kg^-1) ,however, can dropped their activity, as the increasing of mercury concentration in soil ,but the content of free praline and MDA and the conductance rate in tobacoo leaf and the activity of ATPase in roots decreased with the increasing concentration of mercury.Forthly the results of study on effects of mercury on metabolism of carbohydrate and nitrogen in flue-cured Tobacco indicate that nitrate reductase (NR) activity droped with the increasing concentration of mercury in soil. Activity of Gultamate-pyruvate transaminase (GPT) had a small quantity of increase under the treatment concentration of 10 mg. kg^-1 Hg or 10 mg. kg^-1 Hg . when the treatment concentration above 10 mg. kg^-1 ,the activity of GPT dropped with the increasing treatment concentration of Hg .mercury added in soil can improve Glutamina synthase (GS) activity, Asparaginase activity and the content of free aminophenol . Sucrose synthase activity present drop direction with the increasing treatment concentration of Hg in soil .Low concentration Hg (≤30mg. kg^-1) has a capability to improve Sucrose phosphate synthase activity ,but the capability would be weaken for higher concentration Hg (>30mg. kg^-1) .To sum up ,amylum synthase activity increased with the with the increasing treatment concentration of Hg ,but range increased decreased. In addition, mercury can improve ADPGppase activity .Fifthly Studied on effects of mercury on the enzyme activity and microbes in soil .results show that urease was significantly inhibiled by the mercury in 10-120mg. kg^-1 ,with the decreasing concentration of mercury in soil ,changes of tryptophan decarboxylase activity did not present evidence rule. Protease activity hoisted when the concentration of mercury in 10-60mg. kg^-1,but the concentration of mercury above 60mg. kg^-1, it activity decreased. Bacteria biomass droped with the increasing concentration of mercury in soil .epiphyte biomass increased under or in the concentration of 30mg/kgHg. it biomass would be decreased when the concentration above 30mg/kg.Sixthly The effects of mercury on quality of tobacoo leaf and the enrichment rule of mercury in tobacoo organs were studied, results indicated that the content of starch total soluble sugars and reducing sugars increased in the concentration of 10mg. kg^-1 Hg and 30mg. kg^-1 Hg,when the concentration of mercury above 30mg. kg^-1, their content decreased .The content of total nitrogen and nicotine and potassium increased under or in the concentration of 30mg. kg^-1 Hg,however their content decreased when the concentration of mercury above 30mg. kg^-1 .changes of chloride content as follows: when the concentration of mercury under 60mg. kg^-1, the content of chloride increased ,when the concentration of mercury above 60mg. kg^-1, the content of chloride decreased in lower leaves, the content of chloride droped with the increasing concentration of mercury.Seventh the enrichment concentration of mercury in tobacoo organs as follows: the order was roots>leaves>stems, lower leaves >middle leaves>upper leaves, the enrichment concentration of mercury in tobacoo organs were positively correlated with the mercury in soil . the concentration of 0.01 mg. kg^-1 Hg tobacoo roots as a criterion to judge whether mercury had contaminated to growth of tobacoo, result shows that the threshold value of mercury toxicity was 3. 287mg. kg^-1.According to the study, Mercury pollution in soil was harmful to growth of flue-cured tobacco to different extent ,appearance symptom as follows: the roots was short ,thin and brown;strm shorten,area of leaves be minished ,greenness of leaves become tint,even some leaves with lots of small brown spot .Besides,mercury could be mass enriched in tobacoo leaves ,and inhaled with the smoke ,which was harmful to the smoker and others who do not smoke, So it was suggested that polluted area by mercury had better restore before plant flue-cured tobacco.