Controlled-release Lodine/Setenium Fertilizers Improved Iodine/Selenium Accumulation In Vegetables

Iodine and selenium play an important role in human health. Iodine and selenium canlead to human suffering from various diseases.Therefore, how to improve the iodine andselenium concentrations in human food in the prevention of iodine and selenium deficiencydiseases occurrence has the vital significance.Traditional iodine and selenium supplement willhave some disadvantages. Inorganic iodine and selenium could not be well absorbed bybodies and be dangerous to human and even produces toxicity. Therefore, Iodine andselenium will have wide edible valuation only when it is transformed in to biological activeorganic iodine and selenium through food chain.In order to offer academic thereunder for producing, spreading and ecosecurity estimationof controlled-release iodine or selenium fertilizers, several experiments were conducted andbiostatistical method were used in this study. The effects of iodine, selenium and combineduse of iodine and selenium on seed germination, growth and development of plants and so onwere studied by acute toxicity and hydroponic experiment. Potted lettuce experiment wascarried to investigate the influence of controlled-release iodine (IO^-and IO₃^-) fertilizers on theiodine uptake by lettuce as well as on the growth and quality of lettuce and the influence ofiodine on soil leachate. Also, the effects of controlled-release iodate fertilizer and controlledrelease iodate-selenium fertilizers on iodine and selenium uptake, growth and quality ofcherry tomato. The main results were summarized as follows:1. The nutrient release curve of controlled-release iodine or selenium fertilizers in watershowed a shape of "S". The nutrient release curve of controlled-release fertilizers in25℃water showed that release rate increased with time in the first stage, fastigium and decreasedwith time in the third stage. Parameters, like initial nutrient release rate, and release duration,accorded with Chinese National Slow and controlled-release fertilizers standard. Andcontrolled-release iodine or selenium fertilizers could be used for crops application research.2. Lettuce seed germination experiment results showed that seed germination indexes,seedling growth and antioxidative activities were increased with the increase of IO₃^-concentration.When the IO₃^-concentration was80μmol L-1, lettuce seed germination energy,germination rate, germination index and vigor index significantly increased by22.13%²5.23%compared with the control. Lettuce seedling root length, stem length, fresh weightand dry weight reached maximum and improved16.09%¹13.71%compared to control. The SOD, POD and CAT activities of lettuce seedlings were significantly higher than those ofcontrol, increased by32.74%⁶5.71%. And the MDA content has no significant differencecompared with control. Low concentrations of Iˉ(10,20and40μmol L-1) stimulated lettuceseed germination.When the concentration of Iˉwas80μmol L-1, lettuce seed germinationenergy, germination rate, germination index and vigor index decreased by32.78%³6.83%compared with the control. The lettuce seedling root length, stem length, fresh weight and dryweight were the lowest. The SOD and POD activities were the highest when the lettuceseedlings treated with80μmol L-1. The CAT activity of lettuce seedlings increased with theincreased Iˉconcentration, and the content of MDA was significant higher than that of control.The results also showed that the seed germination and seedling growth of lettuce showed asignificant positive correlation with IO₃^-concentration, and showed significantly negativecorrelation with Iˉconcentration. In addition, low concentration of IO₃^-and Iˉor SeO₃^2-interactions promoted seed germination of lettuce, stimulated the growth of seedlings, andincreased seedling enzyme activity resistance. However, high concentrations of Iˉand SeO₃^2-interaction significantly inhibited lettuce seed germination.3. The growth parameters (plant height, stem diameter, leaf area, and dry weight) andphysiological attributes (root activity, chlorophyll (Chl) content, net photosynthetic rate (Pn),stomatal conductance (Gs), transpiration rate (Tr), and contents of proline, protein and sugar)were the greatest in the plants developed from the combination of IO₃^-and SeO₃^2-. Theincreased activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) andascorbate peroxidase (APX) were enhanced by22.25%,16.74%,31.82%and37.58%,respectively, and the lipid peroxidation was decreased by20.32%, in comparison to control. Incontrast, the combined use of Iˉand SeO₃^2- resulted in reduced growth. The plant height andleaf number were decreased by19.10%and7.14%, respectively. The seedling shoot freshweight and dry weight was significantly lower than the control, were reduced by25.64%and26.32%. The combination of Iˉand SeO₃^2- resulted in reduced photosynthesis capacity as wellas reduced activities of antioxidant enzymes, and led to serious lipid peroxidation in plants.Plants grown with Iˉalone were taller (9.1%) and more sensitive to leaf photosynthesiscompared to those with IO₃^-supply alone, whereas the activities of antioxidant enzymes andprotein content were comparable. SeO₃^2- application alone generated marginal effects onmeasured characteristics. Overall, combined use of IO₃^-and SeO₃^2- proved to be the optimumfor boosting growth in this experiment.4. A greenhouse pot experiment was conducted to assess the effects of controlled-releaseiodine fertilizers on the iodine accumulation and physiological response of lettuce in comparison with traditional iodine fertilizers. The plants were subjected to different iodinefertilizers containing two levels of iodine as iodate or iodide at10and20mg kg-1soil. Resultsshowed that all the treatments with iodine applied significantly increased concentrations ofiodine and water-soluble iodine in the leaves of lettuce. Leaf iodine nutrition developed fromcontrolled-release potassium iodate and controlled-release potassium iodide was significantlyenhanced by46.60%⁶1.16%and46.59%⁵8.53%in comparison with correspondingtraditional iodine fertilizers, respectively. The biomass product (fresh mass and dry mass ofshoot and root) and leaf chlorophyll content of lettuce grown with controlled-release iodinefertilizers were higher than those of traditional iodine fertilizers. The growth-promotingfunction was also associated with increased content of vitamin C and activities of superoxidedismutase (SOD), peroxidase (POD) and catalase (CAT) in lettuce leaves. Application ofcontrolled-release iodine fertilizers resulted in reduced NO₃^--N content and diminished lipidperoxidation (MDA) content of lettuce leaves. The iodine uptook by lettuce mostly retained inthe root and lettuce absopted more iodine when the iodate applied. The iodine accumulation inlettuce plants treated by controlled-release iodine fertilizers was much higher than that of thetraditional iodine fertilizers treatment. The iodine content in leachate peaked withcontrolled-release iodine fertilizers were later than those with the traditional iodine fertilizers.Controlled-release potassium iodate and controlled-release potassium iodide also significantlyreduced the iodine leached rate by45.99%⁵0.97%and39.18%⁴6.29%compared totraditional fertilizers, respectively. When iodine applied rate was20mg kg^-1soil, the leafiodine content was significant higher than that of10mg kg-1soil, whereas no significantdifference was found in other indexes. Overall, controlled-release iodine fertilizers increasediodine accumulation in lettuce leaves, prevented iodine leaching and improved iodine useefficiency, proving to be the optimum for cultivating iodine-enriched vegetables. Whencontrolled-release iodate fertilizer was used as10mg kg-1soil, the iodine concentration inlettuce leaves reached8.09mg kg^-1. The iodine deficiency populations can eat quantitativelettuce to meet their daily iodine demand150μg d^-1. When the applied dosage was20mg kg^-1soil, it may lead to excessive intake of iodine in lettuce and iodine waste.5. The pH value of soil leachate had no significant difference compared with the control.The application of iodine in soil did not impact the acid-base equilibrium. The EC valuechanged more stable when the soil treated by controlled-release iodine fertilizers. Theapplication of iodine in soil could promote the leaching of K⁺, Na⁺, Ca²⁺, Mg2+and inorganicnitrogen.6. The potted cherry tomato experiment showed that the concentrations of iodine and selenium in fruits were significantly enhanced when iodine and selenium applied. Theconcentrations of iodine in fruits treated by the controlled-release iodine fertilizer andcontrolled-release iodine-selenium fertilizers increased by35.58%and28.53%compared tothe traditional iodine fertilizers. The concentrations of selenium in fruits treated by thecontrolled-release selenium and controlled-release iodine-selenium fertilizers increased by10.89%and13.86%, respectively. Applications of controlled-release iodine fertilizer andcontrolled-release selenium fertilizer resulted in significant higher iodine and seleniumaccumulation in fruits, increased by38.78%and19.40%. The organic seleniumconcentrations and conversion rate in cherry tomato fruits treated by controlled-releaseselenium fertilizers increased by5.19%and3.36%, respectively, comparing with traditionalselenium fertilizers. The cherry tomato fruit yield and content of vitamin C increased unferthe application of controlled release fertilizers. In addition, application of controlled-releaseiodine-selenium fertilizer and controlled-release fertilizer caused iodine leaching ratesdecreased by49.02%and37.25%. When applying the controlled-release selenium fertilizerand controlled-release iodine-selenium fertilizer in the soil, the soil iodine leaching ratesdecreased by38.91%and46.61%, respectively.