Differences Of Selenium Uptake Pattern Of Plants And Possible Mechanism When Amended Selenate And Selenite

Selenium in plant is an important part in humn diet for improving selenium levels.Growing plants enriched with selenium could be an effective way to reduce dietarydeficiencies and increase health benefits. There are many factors to influence the seleniumcontent in plants, including varieties, selenium uptake and tolerance ability, growth period ofplants, the selenium speciation and concentration of soil and other environmental facors.Tobetter understanding combined effects of selenium speciation and plant varieties on seleniumbioavailability, it is necessary to clarify the differences of plant selenium uptake ability withgrowth period and possible mechanism. In this study, pot experiment and lab analysis werecarried out to examine the differences of selenium uptake pattern on7plants (pakchoi, carrot,broccoli, purple cabbage, flowering chinese cabbage, mustard and wheat) when amendedselenate and selenite. Meanwhile, the dynamic changes of soil available Se, plant biomass andphysiological metabolism were analyzed to explore the mechanism. The main results were asfollows:1. No significant differences were observed in pakchoi shoot biomass between selenateand selenite treatment in the whole growth period. The Se concentration in pakchoi decreasedrapidly across the growth period in the selenate treatments, while which increased in theselenite treatments. In the selenate treatments, the pakchoi shoots Se concantrations weresignificantly higher than the roots, but the opposite results were found in the selenitetreatments. In the whole growth period of pakchoi, Se concentrations in selenate treatmentswere2-60times of that in selenite treatments. The content of available Se in soil slightlydecreased with the growth of pakchoi in the selenite treatments, but it decreased rapidly in theselenate treatments. The significant correlations between soil available Se and Seconcentration in shoots and roots of pakchoi was found in selenate treatments, the correlationcoefficients was0.901and0.864, respectively. On the contrast, no significant correlationswere observed between soil available Se and Se concentration of roots and shoots in selenitetreatments. The results indicated that the differences between the Se uptake pattern of selenateand selenite on pakchoi was the comprehensive function of the ability of soil providing Seand crop uptake Se ability. 2. Soil speciation analysis showed that after one month of growing season, the content ofsoluble forms of Se (VI) reduced significantly in the selenate treatments (P <0.05), andmainly existed in exchangeable and carbonate-bound form, which accounted for about70%oftotal Se in the soil. While it still existed in exchangeable and carbonate-bound Se (IV) in theselenite treatments that was the same with the peiod before planting. Partial correlationanalysis showed that the soil soluble Se (VI) forms in selenate treatments and exchangeableand soluble Se (IV) forms in selenite treatments had better bioavailability for pakchoi. Andthe change of organic bound Se before planting and afer harvested of pakchoi had bettercorrelation to the pakchoi Se content (P <0.01). It showed that organic bound Se can be usedas a potential source of Se for plants. The IRvalue of Se in all treatments increasedsignificantly after planting pakchoi (P <0.05). And in the selenate treatments it was increasedmore obvious than the selenite treatments. Therefore, each forms of Se in the soil graduallyinto balance. In the selenate treatments, the Se absorption by pakchoi was17.1%~24.6%ofthe total soil Se, while it was only1.6%~1.9%absorbed by pakchoi in the selenite treatments.It indicated that the difference between the bioavailability of selenate and selenite on pakchoiwere the differences of the speciation and valence state of Se in soil.3. In the whole growth period, the Se concentration in the6plants increased in the first6weeks in the selenite treatments, and then flattens out. Among them, the overground Secontent of carrot, mustard and wheat goes down after the6weeks, while the underground Seconcent in the6crops rising in the whole growth period. The Se content in crops decreasedrapidly across time in the selenate treatments except mustard. The TF of the6crops decreasedgradually across time in the selenite treatments, among them, the TF of carrots were thelargest, the value up to2.28~3.33, while the TF of other5crops were less than1. In theselenate treatments, the TF of crops decreased as well except for the mustard, among them,the TF of wheat could up to3.2~5.6, and the TF of all the crops were greater to1during thewhole growth period. The significant correlations between soil available Se and Seconcentration in shoots and roots of6crops were found in selenate treatments, while nosignificant correlation was observed between soil available Se and Se concentration of rootsand shoots in selenite treatments. The results indicated that the differences between the Seuptake pattern of selenate and selenite on the6crops were the comprehensive function of thecrop uptake Se ability, the biological dilution and the ability of soil providing Se. So it isimportant to select appropriate Se enrich crops and consider the dynamic changes of Secontent of crops to produce selenium-enriched crops and provide a theoretical basis ofphytoremediation to selenium contaminated soil.4. Selenium can significantly affect the crop growth. Selenite in2.5mg·Se·kg-1could stimulate the growth of broccoli, purple cabbage and flowering chinese cabbage, while it wassignificant inhibit the growth of carrot, and characterized by root length inhibition ratereached51.13%. While2.5mg Se·kg-1of selenate exerted toxic effects on6crops, and theendurance capacity about purple cabbage and broccoli were the best, while the mustard wasthe weakest.2.5mg Se·kg-1of selenite and selenate could inhibit the antioxidant activity ofmustard, and showed up as induce the activity of CAT and POD, and the decrease of prolinecontent. While2.5mg Se·kg-1of selenite could inhabit the GSH-Px activity of carrot andwheat. Above them, the antioxidation enhanced of the crops when applicated with selenateand selenite, principally showed that the activities of the GSH-Px, SOD and proline wereenhanced, and the MDA contents were induced. And the antioxidations of the6crops in theselenate treatments were greater than the selenite treatments.It were differences of selenium uptake pattern of plants when amended selenite andselenate, and the possible mechanism were the ability of soil providing Se, crop uptake Seability and the differences of the physiological metabolism. So it had certain guid toreasonable application of selenium fertilizer and production of Se-enrich crops.