Effect Of Silane Coupling Agent (KH550) Modified Palygorskite On Tomato Growth In Heavy Metal Contaminated Soil With Cd?Pb And Zn

At present,contaminated soil with heavy metals has become a global problem,due to its high damage,long pollution period,and difficulty in removal,which has serious impact on the safe production of grain in China.Therefore,there is an urgent need to to remedy contaminated soil with heavy metals.In the repair methods of contaminated soil with heavy metals,adding soil amendment to the soil is a common repairing method.Clay minerals such as montmorillonite,sepiolite and palygorskite have been widely used to repair contaminated soil with heavy metals.As a kind of hydrated magnesium aluminum silicate clay,palygorskite has advantages of large specific surface area,abundant surface groups and fine pores,large adsorption capacity,low cost and environmental protection.It has been paid more and more attention in the application of heavy metal contaminated soil remediation.It is also a hot spot to improve the repair performance through physical and chemical modification.In this paper,natural palygorskite?PAL?and the palygorskite modification?KH550-PAL?are used as soil amendments.An experiment was conducted to investigate the toxicological effects of modified palygorskite?KH550-PAL?on the growth of tomato plants on heavy metal contaminated soil,leaf nitrogen content,photosynthesis ability to tomato grown in contaminated soil with Cd,Pb and Zn,also the available of heavy metals and heavy metals?Cd,Pb and Zn?distribution in tomato soils.The aim is to reveal the mechanism of the effect of KH550-PAL addition on the growth of tomato on soil contaminated with heavy metals?Cd,Pb and Zn?.The research of this paper is helpful to further explore the repair mechanism of KH550-PAL on heavy metal contaminated soil,and provide theoretical basis and technical support for better repair of heavy metal contaminated soil.The main findings of the paper are as follows:?1?The application of KH550-PAL reduced the accumulation of heavy metals?Cd,Pb and Zn?in tomato roots by 39.62%,60.25%and 48.94%,respectively,the bio-concentration factors of heavy metals in tomato plants decreased by 59.52%,38.23%and 62.26%,respectively,indicating that the application of KH550-PAL significantly reduced the accumulative effect of heavy metals on tomato plants.?2?Both the modified KH550-PAL and unmodified PAL can reduce the toxicity of heavy metals in the soil to tomato.The application of PAL to heavy metal contaminated soil reduced the MDA content,H₂O₂ content,O₂.^-production rate and non-photochemical quenching?NPQ?of tomato leaves by 34.77%,55.43%,23.23%and 42.97%,respectively.The application of KH550-PAL reduced the MDA content,H₂O₂ content,O₂.^-production rate and non-photochemical quenching?NPQ?of tomato leaves by 89.36%,25.27%,74.45%and 81.67%,respectively.Meanwhile,we found that tomato foliar superoxide dismutase?SOD?,glutathione reductase?GR?and catalase?CAT?activities increased by 228.57%,238.64%and 196.42%,respectively.Compared to natural palygorskite treatment.It is indicated that after applying KH550-PAL in heavy metal contaminated soil,tomato plants accumulate less heavy metal content,which can decrease the oxidative stress of heavy metals on plants by enhancing the antioxidant enzyme defense and reducing heat dissipation in the body,thereby improving the photosynthetic electron transport of photosystem II and growth of tomato.?3?Heavy metals may inhibit the absorption of nitrogen by plants.Compared to heavy metals contaminated soil without amendment,the application of KH550-PAL increased the nitrogen content per unit area and the chlorophyll content per unit area of tomato plants by 37.21%and 45.25%,respectively,while photosynthesis parameters of tomato plants such as potential maximum net photosynthetic rate(P_max),maximum carboxylation rate(V_cmax)and maximum electron transfer rate(J_max)were increased by 68.33%53.20%66.13%,respectively,which promoted the growth of tomato plants.?4?The application of KH550-PAL changed the morphological distribution of heavy metals?Cd,Pb and Zn?in tomato soil.Compared to heavy metal contaminated soil without amendment,the addition of KH550-PAL reduced the ionic Cd,which is easily absorbed by plants from 73.50%to 53.85%,the carbonate-bound Cd which is not easily absorbed from 5.28%to 14.19%,and the Cd of residual fraction from 8.37%increased to 13.31%;the morphological changes of Pb and Zn also showed similar trends.Compared to heavy metals contaminated soil without amendment,the application of PAL decreased the availablity of heavy metals?Cd,Pb and Zn?in tomato soil by 25.38%,49.45%and 34.28%,respectively.Therefore,the exchangeable heavy metal?Cd,Pb and Zn?morphological content is reduced,from unstable forms to more stable directions,and the migration of heavy metals in the soil is reduced.