| Zinc(Zn)is an essential micronutrient for all organisms,which plays a catalytic and regulatory role in corns.The study of Zn isotope fractionation is a new technology,which can help us better understand the absorption,transport and tolerance mechanism of corns to Zn,and trace the source and transfer process of Zn.Therefore,the characteristics of Zn isotope provide a potential tool for tracing the absorption and transfer mechanism of Zn in soil-corn system.The study of mass spectrometry technology shows that different environmental conditions and physiological states of corns lead to different levels of isotopic fractionation in the process of biological absorption and transport of Zn isotopes.The existence of isotope fractionation in corns,especially the biogenic Zn isotope fractionation,will help us to understand the process of land Zn cycle more comprehensively.The growth of corns depends on the soil,which is the source and sink of heavy metals.Microorganism is an important part of soil,which can produce various chelating agents and metal carriers.It can affect the mobility and utilization of heavy metal elements in corns through a series of metabolic functions such as biosorption and enrichment,dissolution and precipitation,oxidation-reduction,etc.It can also change metal morphology,enhance metal solubility,and increase low mobility minerals in soil.The supply of nutrients(such as P,Zn,Cu)can promote the circulation of nutrients and improves the growth and productivity of corns.Under the interaction of microorganisms,soil and corns,Zn isotope fractionation may occur.Therefore,in this study,maize was corned in the soil with natural conditions,sterilization conditions and microbial reconstruction conditions after sterilization,and the characteristics of dissolved organic carbon(DOC),p H and Zn concentration in pore water of corn and non corn soil changed with time under different microbial conditions.The effects of root soil and pore water on Zn isotope composition in maize roots,stems,leaves and grains were studied.The characteristics and mechanism of Zn isotope fractionation in soil corn system under different microbial conditions were discussed.A comprehensive model for coupling stable Zn and Zn isotope fractionation in corns was established.(1)In the presence of corns,DOC content and Zn concentration in soil pore water are relatively high,and p H value is relatively low.The more species and quantity of microorganisms,the more enriched heavy Zn isotope in soil pore water;in the absence of corns,the DOC content in soil pore water is relatively low,and the p H value is relatively high.The less the types and quantity of microorganisms,the more light Zn isotope is enriched in soil pore water.The existence of corns increased the fractionation degree of Zn isotope,and the higher the fractionation degree was with time.(2)The species and quantity of microorganisms were negatively correlated with DOC content,Zn concentration and p H value.The higher the consumption of DOC,the lower the concentration of Zn and the lower the p H value,the greater the fractionation degree of Zn isotope in soil pore water,and the relative enrichment of heavy Zn isotope;the less consumption of DOC,the higher the concentration of Zn and the higher p H value,the smaller the fractionation degree of Zn isotope in soil pore water,and the relative enrichment of light Zn isotope.(3)Under the natural conditions,the biomass of each part of the corn was larger,the concentration of Zn was lower,the biomass under sterilization was smaller,and the concentration of Zn was higher.The biomass and Zn concentration under the reconstructed microbial condition after sterilization were between the other two groups.The existence of microorganisms can promote the growth of corns and inhibit the accumulation of Zn in various parts of corns.Under different microbial conditions,biomass of root,stem,leaf and grain showed positive correlation with Zn isotope fractionation degree,while Zn concentration showed negative correlation with Zn isotope fractionation degree.(4)Heavy Zn isotopes are relatively enriched in roots and light Zn isotopes are relatively enriched in aboveground parts(stems,leaves and grains).Under natural conditions,the degree of Zn isotope fractionation is the largest,while that under sterilization is the smallest.The degree of Zn isotope fractionation under the condition of reconstructed microorganisms after sterilization is between the other two groups,which indicates that the existence of microorganisms promotes the fractionation of Zn isotopes in aerial parts of corns.(5)The degree of Zn isotope fractionation among corn parts depends on the transport degree of Zn from root to shoot.Each part of corn is a flow system.In this system,the transfer of Zn between corn tissues and cells leads to Zn isotope fractionation.The box model of Zn mass balance and isotope fractionation in soil corn system under different microbial conditions showed that the higher the concentration of Zn in different parts of corns,the lower the observed Zn isotopic fractionation,the lower the enrichment of Zn in different parts of corns,and the lower the observed Zn isotopic fractionation.(6)The isotopic fractionation models of Zn transport from soil to pore water,from pore water to root,root radial transport and distribution in corns were established.The fractionation process of Zn in soil corn system was described qualitatively.Combined with Rayleigh fractionation model,a comprehensive model was established to link the steady-state Zn and Zn isotope fractionation in corns.The fractionation characteristics of Zn in soil corn system were quantitatively analyzed.In this project,the effect of microorganisms on Zn isotope fractionation in soil corn system was studied,which accumulated research experience for more comprehensive understanding of the biogeochemical cycle of Zn in soil corn system,and laid a certain theoretical foundation for comprehensive treatment of Zn contaminated areas with microorganisms as adsorbents. |
PDF Full Text Request