Effects Of Selenium Combined With Zinc Amendment On Selenium And Zinc Bioavailability In Soil And Mechanisms

Selenium(Se)and zinc(Zn)are essential micronutrient for human and animal health.The application of Se and Zn fertilizer in soil can increase the content of Se and Zn in plants(foods),which is the major safe way to solve the global deficiency problem of Se and Zn in human body.The co-amendment of Se and Zn can affect the content of Se and Zn in plants,but no systematic studies on the Se-Zn interaction on the bioavailability of Se/Zn in soil had been reported yet.Consequently,in this study,pot experiment was conducted to explore the effects of the interaction between two Se species(selenite and selenate)and Zn on the plant growth,Se/Zn uptake and translocation of pak choi.The change of Se/Zn fractions,soil enzyme activity during the process were also determined,in order to investigate the effects of Se-Zn interaction on soil Se/Zn bioavailability and its mechanism.The main results were as follows:1.The co-amendment of Se and Zn alleviated the toxic effect of high selenate on Pak choi.Application of 2.5 mg/kg selenate had a significant toxic effect on the growth of pak choi,which was indicated by the shoot height,and rapid biomass decline of pak choi(19.1-40.4%).Synergistic effect was observed from selenate(2.5 mg/kg)combined with Zn on growth of pak choi,which indicated that application of Zn alleviated the toxic effect of high selenate on pak choi.2.Effect of Se combined with Zn amendment on soil Zn bioavailability was related to the application of Zn.When the application of Zn was 20 mg/kg,the co-amendment of Se and Zn could make Zn as the available forms(mainly exchangeable Zn and the organic matter weakly bound Zn)for plants,which increases the bioavailability of Zn in soil.Nevertheless,only the co-amendment of selenite and Zn(20 mg/kg)promoted the translocation of Zn in pak choi,which showed that the Zn concentration in the shoots of pak choi was significantly increased by 27.2%–31.1% comparing with corresponding single Zn treatment;the coamendment of selenate and Zn had no significant effect on the Zn concentration in pak choi.In addition,the potential available Zn content in soil(weakly bound to organic matter and carbonate bound Zn)was positively correlated with the Zn concentrations in pak choi,indicating that these indexes can be used to predict the bioavailability of Zn in soil.3.Effect of Se combined with Zn amendment on soil Se bioavailability was related to the species of Se.For the selenite-zinc co-amended treatments,the Se(VI)content of the available Se(soluble and exchangeable Se)increased significantly by 37.1-80.3% comparing with the corresponding single Se treatment,which was embodies in sharply increase of Se concentration in the shoots of pak choi and significant decrease of Se concentration in the root of pak choi.Notedly,the translocation factors of selenite treatments(single or with Zn)were less than 1.For the selenate-zinc co-amended treatments,the proportion of soluble and exchangeable Se to the total Se increased significantly,which showed that the Se–Zn coamended treatments inhibited the transformation of Se to the stable state,making Se as the available forms to plants.The concentration of Se in the root of pak choi also increased significantly(26.8-149.9%)in the corresponding treatment compared with the single Se treatment.Notedly,the translocation factors of selenate treatments(single or with Zn)were greater than 1.4.Se combined with Zn amendment significantly affected soil enzyme activity and enzyme function diversity.For Se–Zn co-amended treatments,alkaline phosphatase and catalase activity was significantly stimulated,invertase and urease activity were inhibited.Exchangeable Zn and manganese oxide bound Zn had a significant negative effect on soil invertase and urease activities,and soil urease had a negative effect on soil exchangeable Zn and manganese oxide bound Zn.There is a negative correlation between soil enzymes and soil available Se(soluble and exchangeable Zn).The Se combined with Zn amendment showed antagonistic effect on soil enzyme function diversity index(geometric mean,weighted average,total enzyme activity),and soil Zn fractions(except residue Zn)could significantly affect these indexes(negative effects),indicating that these three diversity indexes could better characterize the effect of Zn availability on soil enzyme ecological function.Generally,this study shows that the interaction of Se and Zn has a significant impact on the bioavailability of Se and Zn in soil.This study recommended 1 mg/kg selenite and 20 mg/kg zinc treatment as the best scheme for the co-biofortification of Se and Zn,which provide a scientific reference for Se and Zn biofortification of plants in calcareous soil.