Importance Of Plant Species And Soil Types To Silicon Stable Isotope Fractionation Of Plant

Silicon(Si)is the second most mass-abundant element on the earth's surface.There are numerous beneficial effects of Si on the growth,development,yield,quality,stress resistance observed in a wide variety of plant species.In recent years,with the rapid development of the stable Si isotope testing and analysis technology,it is frequently used to understand the biogeochemical behavior of Si.However,the knowledge of performance of Si isotope compositions in plants is still rare.Thus,the objective of this study is based on Si isotope fractionation in rice,cucumber and tomato and its regulation mechanism by soil property to understand biogeochemical Si cycle and mechanism of Si absorption,transportation and deposition in plants.The main results are as follows.1.The results obtained from rice,cucumber and tomato planted in hydroponics showed that Si isotope fractionation occured during the transportation and deposition of Si in plants.At 0.08 mM,0.8 mM and 1.6 mM Si levels,the 830Si values in rice shoot were-0.17‰,-0.46‰ and-0.66‰,andcucumber shoot were-0.08‰,-0.25‰and-0.3 8‰,andtomato shoot were-0.32‰,-0.34‰ and-0.44‰,respectively.The?30Si values in rice,cucuber and tomato shoot were all accorded with the law of terminal distribution,exhibiting a progressive increase from lower to upper organs.The ?30Si values in rice root were 0.05‰,-0.16‰ and-0.23‰,and cucumber root were 0.01‰,-0.06‰ and-0.10‰,and tomato root were-0.19‰,-0.34‰ and-0.39‰,respectively,which displayed that in rice,cucuGber and tomato,the ?30Si values in root were higher than that in shoot.Furthermore,we observed the ?30Si values of dissolved Siin the rootwerehigher than the values of depositional Si in the shoot.2.The results obtained from rice,cucumber and tomato planted in hydroponics showed that Si isotope fractionation occured when plants absorbed Si from the solution.At 0.8 mM and 1.6 mM Si levels,the Si isotope fractionation factor(30?planant-surce)between the bulked rice and source were-0.51‰ and-0.70‰,indicating that compared with heavy silicon isotope,rice preferentially absorbed light silicon isotope.At 0.08 mM,0.8 mM and.6 mM Si levels,the Si isotope fractionation factor(30?plant-source)between the bulked cucumber and source were-0.14‰,-0.30‰and-0.43‰,and the Si isotope fractionation factor(30?plant-source)between the bulked tomato and source were-0.40‰,-0.43‰ and-0.52‰,illustrating that like rice,cucumber and tomato were also more likely to uptake the light silicon isotope than the heavey silicon isotope.3.The results of rice grown in different soil types showed that different types of soil had a significant impact on the rice Si-isotopic fractionation.The Si isotope fractionation factors(?Pre-Dis)of rice planted in red soil,black soil and cinnamon soil were 0.9988,0.9978 and 0.9975,respectively,illustrating that the extent of Si isotope fractionation of rice planted in cinnamon soil was the strongest,followed by rice in black soil and rice in red soil.Correlation analysis showed that the ?30Si values of bulk rice,the ?30Si values of rice leaveswere significant correlated with the contents of organic matter,available Si,free Fe oxides,free A1 oxides and pH values of soils(P<0.01),indicating that rice Si-isotopic signature might be primarily affected by pH values,organic matter content,available Si content of soils and the extent of soil weathering since the contents of free Fe oxide and free A1 oxide increase with weathering.