Regulation Procedure Of Sulphur On The Uptake By Brassica Napus Of Selenium Applied As Selenite

The range of selenium（Se） intake between Se-deficiency and toxicity in humans is rather narrow, frequent intake of a significant amount of Se leads to an increased risk of Se toxicity. The distribution of Se in soils is usually heterogeneous and site-specific. There are two famous Se-rich regions in the world where have been identified in Enshi and Ziyang in china, the regions which produce the Se-rich products have become more and more popular in the market. Therefore, when emphasized the fact to enhance Se nutrition in Se-deficient areas, developing reasonable agronomic measures to regulate Se content in crops in high-Se areas also has important practical significance. Since sulphur（S） and Se have the similar chemical and physical properties, the Se-deficiency and toxicity in plants often were considered due to the interaction effects of S and Se. Recently, with the increasing application of high concentrations of non-S fertiliser and the decreasing application of organic fertiliser, crop S deficiency is becoming more frequent. Therefore, using S fertiliser has a broad application prospect for regulation Se content, supporting the economic development, and enhancing the safety of agricultural production in Se-rich regions. Previous studies were focus on the interaction of S and selenate, but the interaction of S and selenite, the effects of S on the uptake and translocation of Se by B. napus treated with selenite and selenate are not well reported in the current literature. Based on the resluts in the existing research, pot, hydroponic and field experiments were conducted to evaluate the relationship between S and Se. The main results as follows:（1）The results showed that the sensitivity of B. napus to selenite gradually decreased through its life cycle. The low concentration of selenite-Se(5 mg?kg^-1) slightly increased the biomass in different parts of B. napus at the different growth stages. The application of excessive selenite-Se(15 mg?kg^-1) significantly reduced the biomass of B. napus grown at seedling stage and winter stage, with decreases of 17.7% and 16.7%, also damage the agronomic traits and yield components of B. napus, which significantly reduced the 1000-grain weight of B. napus（with decrease of 0.12 g）. The application of 150 mg·kg^-1 S significantly alleviated the inhibitory effects on the growth which caused by excess selenite, with the biomass at different stages in B. napus increased from 11.1% to 15.7%. Taken together, the threshold of Se concentration initiating the inhibition of growth varies from the plant age and the S concentration in the medium, the biggest positive effects on the growth of B. napus can be achieved by the combination of an appropriate amount S(≤ 150 mg?kg^-1) and selenite-Se(≤ 5 mg?kg^-1).（2）The results showed that the application of 5 mg?kg^-1 selenite-Se increased the chlorophyll content, ascorbic acid（AsA） and glutathione（GSH） content in leaves of rape seedlings, the application of 10 μmol?L-1 selenite-Se reduced the production of superoxide radical（O2?-） rate in the root system, the two kinds of Se concentrations reduced the activities of superoxide dismutase（SOD）, peroxidase（POD） and fungal catalase（CAT）), which resulted in a reduction of the lipids peroxidation（MDA） content, consequently increasing root activity. Low concentration of selenite-Se stimulated the growth of rape seedlings through improving the root morphology. The positive effects caused by low concentrations of Se significantly weaker than the negative effects caused by high concentrations of Se in the pot(15 mg?kg^-1) and hydroponic（50 μmol?L-1） experiments. The addition of S significantly alleviated the oxidative damage in rape seedlings caused by excessive selenite-Se in the pot experiment, but not hydroponic experiment.（3）The results in the pot experiment showed that the application of S significantly decreased the Se concentrations in various parts and the Se accumulations in shoots of B. napus, with a decrease ranging between 24.7%-64.0% and 20.4%-64.4%, respectively. The Se concentration in B. napus followed the sequence of root > pod > rapeseed > stem, the Se accumulation in B. napus followed the sequence of pod ≈ stem > rapeseed > root, and the distribution ratio was approximately 1:0.97:0.69:0.49, which were not affected by either S rates or selenite rates. Hydroponic experiment also demonstrated that the distribution rate of Se in the shoots and roots of B. napus was not affected by either sulphate rates or selenite rates, which was approximately 1.0: 0.9. In contrast to the pot experiment, the concentration of Se in rape seedlings was not affected by sulphate application rates. The results of pot and hydroponic experiments indicated that the inhibitory effects of S on the uptake of selenite might be not the competition between selenite and sulphate, and sulphate is not involved in the root-to-aboveground translocation of Se in B. napus supplied with selenite.（4）The results showed that the most of Se in the soil treated with selenite can be adsorbed or fixed at the seedling stage of B. napus. Soluble and exchangeable Se（available Se） in soil making up approximately 10%-15% of the total Se. Fe-Mn oxide-bound and organic bound Se（ineffective Se） accounted for 25%-30% of the total Se. Residual Se（invalid Se for seasonal crop） approximately constituted 60% of the total Se. With the same treatment, the soil pH and organic matter content showed no significantly difference at the different stages. The addition of 150 mg?kg^-1 and 300 mg?kg^-1 S decreased soil pH and increased organic matter content significantly, with pH decreased ranging between 014-0.28 units and 0.49-0.63 units, respectively, with organic matter content increased ranging between 1.33-1.79 g?kg^-1 and 1.35-2.12 g?kg^-1, respectively. Therefore, promoting soluble Se transformation to Fe-Mn oxide-bound Se, organic matter-bound Se and residual Se, and inhibited the transformation of Se4+ to Se6+ in the exchangeable fraction, hence reducing the uptake of Se by B. napus in soil culture.（5）The results showed that the Se absorption capacities of B. napus supplied with selenite and selenate were the same at the 0.1 mmol?L-1 sulphate. The addition of sulphate narrowed the uptake difference of Se treated with selenite and selenate mainly by reducing the uptake potential（Vmax） and the affinity（1/Km） of B. napus root. When sulphate concentration in solution was ≥ 2 mmol?L-1, the uptake of Se by B. napus supplied with selenate was not change with increasing of the sulphate rates. The Se translocation capacity from roots to shoots in selenate treatment significantly higher than that of in the selenite treatment. The translocation factor（TF） of Se was significantly reduced by up to 46.4% with increasing selenite in solution, while sulphate had no effect on the Se translocation in the selenite treatment. The TF value of Se was substantially increased by up to 60.5% with increasing selenate in solution, and the application of sulphate appeared to facilitate Se translocation in the selenate treatment. The positive effect of sulphate was more significant with extended treatment time, but unrelated to the selenate or sulfate concentration in solution. These results demonstrated that sulphate is involved in the root-to-shoot translocation of Se in B. napus supplied with selenate, but not selenite.（6）The results in the field experiment showed that the application of 60 kg·hm-2 either element S or sulphate significantly reduced the Se concentrations in various parts of B. napus at maturity stage treated with selenite or selenate, and the two species of S showed the same decreased degree compared to the zero S treatment, with the decreases approximately of 25% under selenite conditions, with the decreases approximately of 45% under selenate conditions. The Se concentration in each part of B. napus with the selenate treatment was 3.0-6.0 times than that of with the selenite treatment, indicating that the uptake of Se by B. napus with the selenate treatment significantly higher than that of with the selenite treatment under the field conditions with application of normal S rates. Se accumulated in the rapeseed meal accounted for more than 99% in the rapeseed, while the ratio in the rapeseed oil less than 1%. The application of either selenite or selenate significantly decreased the contents of erucic acid, sulfuric glucoside and stearic acid content, increased the content of oleic acid, slightly increased the contents of rapeseed oil, rapeseed protein and linoleic acid, decreased the contents of linolenic acid, palmitic acid and eicosenoic acid, and the rapeseed quality of B. napus showed no significantly difference treated with selenite or selenate. There was a further positive effect on the rapeseed quality of B. napus with the element S or sulphate treatment.