Effects Of Selenium Element Nutrition On Growing Development And Selenium Contents Of Flue-cured Tobacco

Through pot experiments in science and technology park of Henan University of Science and Technology in 2008, effects of different application amounts and methods of selenium on tobacco growth, physiological characteristics, and selenium content in tobacco leaves during growth periods were studied, and optimal selenium concentration for flue-cured tobacco growth was proposed. 90 soil samples and 72 tobacco samples including three cultivars of Yunyan87, Yunyan85 and K326 and three gradings of X2F, C3F and B2F were selected in Xuan'en county and Xianfeng county of Enshi autonomous of Hubei province. The distribution and relationship of selenium contents in both soil and flue-cured tobacco were analized. Main results were as follows.1. The effects of selenium on development of flue-cured tobacco(1) The suitable selenium content of soil promoted the flue-cured tobacco growth. When selenium content in the soil was at 0¹2mg/kg, it improved the tobacco height, stem perimeter, the maximum leaf area, the effective leaf quantity, and the dry matter accumulation of above- ground and below-ground at different degrees during different stages of flue-cured tobacco ( P<0.05); when the selenium content in the soil was≥16 mg/kg, compared with the check, it decreased the tobacco height, stem perimeter, the maximum leaf area, the effective leaf quantity, and the dry matter accumulation of above-ground and below-ground during different stages of flue-cured tobacco. When the selenium content in the soil was at 0¹2mg/kg, the tobacco height, stem perimeter, and the dry matter accumulation of above-ground and below-ground in each period were the best. It showed that 8mg/kg selenium content in soil was the best to the growth of flue-cured tobacco. (2) The appropriate selenium spraying to the tobacco leaves promoted the growth of flue-cured tobacco. The effects of spraying selenium on tobacco leaves during the prophase and prometaphase were studied. The results showed that spraying 5μg/ml selenium solution in the prometaphase(ten leaves) increased the tobacco height, stem perimeter, the maximum leaf area, the effective leaf quantity, and the dry matter accumulation of above-ground and below-ground.2. The effects of selenium on chlorophyll and enzymatic activity of flue-cured tobacco(1) Chlorophyll and carotenoid content increased in the right concentration of selenium(0¹2mg/kg); chlorophyll a, chlorophyll b, chlorophyll a+b and carotenoid began to decline when the selenium content≥16mg/kg in the soil, the tobacco leaves occurred deficient chlorosis when the selenium content reached 24mg/kg. The results of selenium solution spraying on tobacco indicated that: 2μg/ml of selenium solution sprayed in the prophase or 5μg/ml of selenium solution sprayed in the prometaphase was the most advantageous for chlorophyll and carotenoid content. The effect of spraying selenium to tobacco leaf was safer than applied sodium selenite to soil.(2) The results of adding selenium to soil experiment indicated that: the activities of POD and SOD increased at first, then decreased during different stages with the increasing of selenium concentration; when the selenium content≤8mg/kg in the soil, the content of MDA among different treatments decreased with the increasing of selenium concentration; and then, when the selenium content >8mg/kg in the soil, the MDA content increased; it showed that higher or lower selenium concentration was not suitable for growth of tobacco, also the appropriate selenium can alleviate membrane lipid peroxidation to a certain extent. The selenium could promoted the invertase activity. The invertase activity in tobacco leaves increased when selenium content in the soil at 2¹2 mg/kg, thus enhencing both carbohydrate metabolism and the amount of carbohydrates. Higher carbohydrate metabolism levels can both provide more carbon skeletons for thee growth of tobacco, the formation of organic compounds, and the transformation and utiliation of assimilate. The using intensity of photosynthate reduced under high selenium level and no selenium. NR activity showed 60d>45d>30d>75d in the different growth stages after treated with selenium. The activity of NR increased at first, then decreased with the increasing of selenium concentration, reached maximum at 8mg/kg respectively. Compared with the check, the activity of NR decreased when the selenium content≥16mg/kg in the soil.(3) The effect of the peroxydase activity (POD) didn't be reflected in short time after spraying selenium to tobacco leaves, but the effect more and more obviously with the extension of time, the action of selenium to SOD was visible in short term, but weaken with the extension of time. The MDA content in the tobacco decreased obviously after spraying selenium, and it lasted a long period. Selenium fertilizer could improve the INV activity after spraying selenium from 2μg/ml to 10μg/ml, and the optimum content was 5μg/ml. INV activity of each treatment showed 75d>60d>45d after translating.3. The effects of selenium on the contents of potassium, total nitrogen and selenium in the growth of flue-cured tobaccoThe contents of total nitrogen and potassium of different tobacco treatments reduced gradually with the growing period extended. With the increasing of soil selenium content, the content of total nitrogen decreased first and then increased in every period while the content of potassium increased first and then decreased. Low Se concentratation(0¹2mg/kg)could reduce the total nitrogen content and increase the potassium content in the development of flue-cured tobacco. The total nitrogen content reached the minimum while potassium content reached the maximum in every period when the concentration of the soil selenium content was 8mg/kg. The nitrogen content of flue-cured tobacco reduced gradually while the potassium content increased gradually with the increase of spray concentration in every period after spraying selenium.As growing period extended, the accumulation rate of selenium in different treatments reached the maximum at seventy-fifth day after transplanting. The accumulation rate of selenium of flue-cured tobacco increased first and then decreased with the increasing of soil selenium content. The accumulation rate of selenium was fastest when soil selenium content at 5¹2mg/kg. With the increasing of spraying concentration, the selenium content in flue-cured tobacco leaves increased gradually and the differences between treatments and contrasts were significant(P<0.05). After spraying selenium at early vigorous growth stages(10 pieces of leaves), the selenium of flue-cured tobacco was gradually translocated to upper and middle leaves as the growing period extended, thereby being unfavorable to selenium accumulation in the lower leaves. Spraying selenium at vigorous growth stages(15 pieces of leaves) could appropriately increase the selenium content in all tobacco leaves. Therefore, spraying selenium solution of 10μg/ml was the best for the accumulation of selenium in flue-cured tobacco leaves.4. Relationships between the soil selenium contents and the selenium content in flue-cured tobacco leaves were analyzed. The results indicated that: (1) The selenium contents in flue-cured tobacco leaves in Enshi were high,ranging from 0.30 to 29.30 mg·kg^-1 with the mean of(8.37±5.83) mg·kg^-1. The content of selenium in flue-cured tobacco among different positions was X2F>C3F>B2F, among different altitudes was medium altitude(800m¹200m) >high altitude (≥1200m) >low altitude(<800m). (2) The soil selenium contents in Enshi tobacco-growing area were high,ranging from 0.28 to 7.03 mg·kg^-1 with the mean of(2.56±1.64) mg·kg^-1.Most of the soil was selenium-rich and high-selenium soil, and 34.44% soils were excessive-selenium soil, with the deepening of the soil thickness, soil selenium contents become lower and lower, and showed the same trend with the selenium content of flue-cured tobacco at different altitudes. (3) There was significantly positively correlation between soil selenium content and selenium content of flue-cured tobacco(correlation coefficient was 0.949). Based on the correlation analysis , the regression equation ,y|^ = -0.1082x³ +1.2494x²-1.9628x+8.1647 was established between soil available selenium and the selenium contents in flue-cured tobacco leaves for 72 samples. Regression equation reached a significant level by F-test.