Effect Of Modified Nano-Carbon Black On Cd And Available Nutrients In Two Plants-Soil Systems

China's farmland soil pollution is dominated by mild and mild heavy metal pollution,with cadmium exceeding the highest rate,reaching 7.0%.Aiming at the pollution characteristics of cultivated land in China,the adsorption and deactivation of heavy metal Cd by oxidized modified nano-carbon black has become a hot research topic.At present,it has been proved by experiments that nano-carbon black?MBC?modified with nitric acid-potassium permanganate can effectively passivate the heavy metal Cd in the soil.However,since the farmland soil needs to grow plants,the passivating agent will adsorb heavy metals at the same time.Does adsorption affect the available nutrients in the soil,which in turn affects plant growth?Understanding this problem is the key to the successful application of modified nanocarbon black to the restoration of actual farmland soil.In this paper,the adsorption characteristics of MBC on NH₄⁺,NO₃^-,HPO₄^2-and K⁺and their effects on the adsorption of Cd by MBC were analyzed through adsorption kinetics experiments,so as to explore the adsorption characteristics of MBC on nutrient ions and the effect of nutrient ions on the adsorption of Cd by MBC.The effects of MBC passivation on available nutrients in Cd-contaminated soils in soil-two plant systems were studied by culture and pot experiments,and the effects of MBC passivation on available nutrients in Cd-contaminated soils were explored.Under the conditions of different water holding capacity and nitrogen fertilizer type,the pot experiment was conducted to explore the effects of water and nitrogen fertilizer regulation on MBC passivation effect and soil available nutrient.The correlation between soil enzyme activity and available nutrients was analyzed by pot experiment.The mechanism of MBC passivation remediation of Cd contaminated soil on available nutrients was discussed by using SOAPaligner software to calculate the abundance information of soil microbial genes.The main results of this paper are as follows:?1?MBC has the fastest adsorption rate of K⁺and the adsorption capacity of NH₄⁺and K⁺is higher than that of NO₃^-and HPO₄^2-respectively.When nutrient ions and Cd²⁺exist in solution at the same time,with the increase of NH₄⁺and K⁺concentration,the adsorption capacity of MBC for cadmium decreases,and the effect of NO₃^-on the adsorption of Cd²⁺by MBC is not significant.High concentration of HPO₄^2-can effectively improve the adsorption capacity of MBC and reduce the concentration of Cd²⁺in solution.?2?Adding MBC can adsorb heavy metal Cd in soil and reduce the content of DTPA-Cd in soil.At the same time,in the process of growth,plants can also reduce the content of heavy metals in soil by absorption,root retention and fixation.Moreover,the combined remediation of passivation materials and phytoremediation has a positive effect on the available heavy metals in passivated soil.Carbon pack analysis experiments have shown that MBC can indeed adsorb Cd in soil.?3?The addition of MBC significantly increased the rate of available NPK in the soil-plant system.The carbon-package analysis experiment proves that the carbon inclusion has no significant effect on the available nitrogen content while adsorbing passivated heavy metals,but it will obviously adsorb fast-acting phosphorus and available potassium.Therefore,in practical applications,the passivating agent MBC and phosphorus and potassium fertilizer should be avoided at the same time.?4?The increase of soil moisture within a certain range contributes to the migration of Cd²⁺to the surface of MBC and reduces its bioavailability,thus promoting the repair of Cd-contaminated soil.At the same time,it is also conducive to the conversion of soil nutrients to quick-acting nutrients,so that plants grow better.Artificial application of nitrogen fertilizer to the soil is conducive to the growth of plants.Compared with NaNO₃,when urea is used as the additional nitrogen fertilizer,the soil available Cd content is lower and the plant grows better.The effect of water regulation on soil DTPA-Cd content was more significant,while the regulation of nitrogen fertilizer type had a more significant effect on the available NPK content.?5?Through high-throughput sequencing of the five treatment groups,39 species of the same species were found in different treatment groups.Among them,there are3 genus of nitrogen-functional bacteria and 2 genus of phosphorus-transforming bacteria.It can be seen from the species abundance value that the abundance of the nitrogen-functional bacteria and the phosphorus-transforming bacteria in the treatment group with MBC increased significantly compared with the treatment group without MBC,thereby increasing the available N and P contents in the soil.?6?By measuring the number and proportion of soil microbial functional gene sequences in five treatment groups,23 microbial functional genes were obtained,and the function of the microbial functional genes with the largest proportion was the transport and metabolism of amino acids,and there was no significant difference among the five treatments.It shows that MBC does not affect the normal growth and metabolism of microorganisms.?7?After being added to the soil for 50 days,MBC can significantly increase the activities of soil urease,acid phosphatase and catalase,and inhibit soil dehydrogenase activity.There was a significant and even significant negative correlation between urease and acid phosphatase activity and soil DTPA-Cd content.The results of regression fitting optimization showed that there was a significant or extremely significant exponential negative correlation between Cd content in soil and urease and acid phosphatase activity.This indicates that the higher the content of Cd in heavy metals,the deeper the effect on urease and acid phosphatase in soil.?8?Preliminary screening with 1 mmol/L Cd²⁺medium,6 resistant strains in ryegrass treatment group,4 resistant strains in red beet,and no treatment in MBC treatment group A strain resistant to cadmium endophytes.It is directly proved that MBC can effectively reduce Cd in soil and can grow normally without the synergistic symbiosis of plant endophytes.