Silicon Isotope Compositions And Distribution Patterns Of Si And Others Nutritional Elements In The Different Absorbing-silicon Plants

Silicon (Si) is the second most mass-abundant element after oxygen in the Earth’s crust. From unicellular algae to vascular plants, it has been reported that almost all organisms are found to produce siliceous structures. Si is taken up into plants as the intact molecule of the amorphous H4SiO4from the root. Its uptake may be the un-preferential passive absorption, and the H4SiO4was transported to the stem by the effect of the transpiration streaming in the xylem. Accompanied by the process of transport into the different organs, the H4SiO4gradually dehydrated, and finally precipitated in the cell lumen, cell walls or the outer structure of the cell as the form of SiO2-n(H2O). Nowadays, the beneficial effects of Si on the growth, development, yield and disease resistance have been observed in a wide variety of plant species. Dissolved Si is absorbed in large amounts by terrestrial vegetation and weathering of silicates removes CO2from the atmosphere. Thus, there is a steadily growing scientific interest in the plant physiology and biogeochemistry of Si.Although Si is traditionally not considered as essential element for plants, it has been demonstrated that Si can affect the mineral nutrients of the higher plant. The available Si was significantly inhabited the rice’s uptake of the P. Mg. Mn, Zn and so on. and also affect the absorption of the N and K. Si. as the beneficial element, can also improve the oxidation-reduction ability for the rice roots, decrease the toxicity of the Fe and Mn, enhance the availability of the soil phosphorus, and improve the utilization ratio of the rice phosphorous. The previous studies about Si were mostly focused on the ability of improving the plant growth, and the mechanism of the biotic and abiotic stress. However, the results were just applied to the siliconphile plants, such as rice. The report about the uptake and distribution characteristics of the Si and other elements on the non-siliconphile plants is still scarce. The general objective of this study is to compare the characteristics of Si kinetic isotope fractionation, content and distribution in the different organs of the silicon and other elements, based on the different siliconphile plants (maize, rice) and non-siliconphile plants (cucumber, Chinese watermelon, tomatoes). The main results are summarized as follows: (1) The results showed that the distribution of silicon in the different organs of maize, cucumber and Chinese watermelon were all accorded with the law of terminal distribution, and the content of silicon followed the trends:leaf, stem> root. Compared with the non-siliconphile plants, the content of silicon in the parts of root, stem and leaf were significantly increased in the siliconphile plants. Besides, the content of silicon was largest in the leaf, lowest in seed and root and stem at an intermediate position, indicating that lots of silicon may be accumulated in the leaf and stem parts as the deposited form, and restrains the transformation of the silicon to the organs of generation. The content of nitrogen and potassium in different organs of maize were closely related with the content of silicon, following the trend of leaf> root> stem. Compared with the siliconphile plant (rice), the amounts of Ca. Mg, Mn, Fe, and Zn in the non-siliconphile plants, such as cucumber, Chinese watermelon, tomatoes, were all significantly increased. What’s more, the content of silicon in different organs of siliconphile plant was also showed the regional distribution, and affected by some factors, such as environment. soil silicon content and so on.(2) The silicon content of the different organs in the siliconphile plants (rice) and non-siliconphile plants (cucumber) were increased with the increasing of the Si concentration in the substrate, followed the trend:high Si concentration> low and intermediate concentrations. There was no significant difference between the intermediate and high Si concentrations in the aboveground organs for rice plant, while the different parts of cucumber between the low and intermediate concentrations also showed no significant difference. In a word, the Si concentration in the siliconphile plant was significantly more than that in the non-siliconphile plant.The contents of N, P, K, Ca, Mg, Fe, Mn, Cu, and Zn in the different organs of the siliconphile plants, excepted the Na, were similar as the distribution of Si content, reduced with the increasing of the outer Si concentration in the substrate. As for the non-siliconphile plants, its contents of N, P and K in the different parts, excepting the N content of root, all reduced with the increasing of the Si concentration. But the macro-and micro-elements showed no significant differences in the different organs. What’s more, the contents of N, P, K, Ca, Na in the cucumber organs were less than that in the rice organs.(3) The silicon contents in the xylem sap for both the rice and cucumber, were more than that in the hydroponics solution under the low Si substrate, indicating that the uptake mode of the H4SiO4in the different absorbing silicon plants was existed mainly as the active absorption, and entering into the roots from the low silicon concentration to the high silicon concentration. While its silicon content in the xylem part of two plants were all similar as that in the outer substrate. In a word, the active absorbing silicon plant adsorbed more silicon content than that the passive adsorbing silicon plant.The high silicon concentration significantly inhabited the rice’s N uptake, while its effect on cucumber was no significance. We speculated that the reasons may be attributed to inhibition absorption of ammonium, rather than the nitrate, under the high silicon concentration. What’s more, the high silicon concentration inhibited the plants uptake of K+, P, Ca, and Mg.Both the siliconphile plant and non-siliconphile plants were consistent with the kinetic isotope fractionation. The distribution of the δ30Si in the solution and aboveground parts of non-siliconphile plants (cucumber) showed a contrary tendency with the siliconphile plants (rice). And the range of the δ30Si fractionation in the siliconphile plant was more than that of in the non-siliconphile plant.