Efficiency And Mechanism Of Ammonium Nitrogen Fertilizer And Organic Acid In Enhancing Tagetes Patula L.remediation Of Cadmium Contaminated Soil

With the acceleration of industrialization and urbanization,industrial pollution and mineral mining activities have caused more and more serious heavy metal pollution in the surrounding soil.Among them,cadmium pollution is the most prominent.As a hyperaccumulative plant,Tagetes patula L.is also an ornamental flower.Herefore,it is of great significance in treating soil cadmium pollution,beautifying the environment and reducing people’s survival risk.This paper takes Tagetes patula L.as the research object.Field experiments show that there is a synergistic effect between humic acid and ammonium nitrogen fertilizer.The combination of the two treatments improved the extraction efficiency of Tagetes patula L.The soil culture experiment was conducted to explore the combined enhancement of polyaspartic acid and ammonium nitrogen fertilizer on the remediation efficiency of cadmium contaminated soil.The results were consistent with the field test results.On this basis,hydroponic experiments were conducted to explore the mechanism of two kinds of chelating agents combined with ammonium nitrogen fertilizer in the remediation of cadmium contaminated soil.The main results are as follows:1.The effects of ammonium nitrogen fertilizer and humic acid on the growth and Cd removal in soil were studied through field experiments.The results showed that nitrogen fertilizer(N)combined with nitrogen fertilizer and humic acid(NHA)could significantly increase the biomass of C.sinensis.Compared with control(CK),the upper biomass of Tagetes patula L.under NHA and N treatments increased by 2.49 and 1.52 times(Feidong soil),2.28 and 1.74 times(Changfeng soil),respectively.NHA treatment can reduce soil p H during the growth of Tagetes patula L.Humic acid treatment(HA)could significantly increase the content of DOC in Feidong and Changfeng soils.NHA and HA treatments could significantly promote the growth and development of the root system and improve the morphological characteristics of the root system.In addition,soil available Cd content increased by 64.1% and 53.1%,respectively,and the cumulative Cd content of Tagetes patula L.increased by 7.17 times and 4.15 times,respectively.The soil Cd removal rate of NHA treatment was the highest,reaching 17.06% and 14.08% in Feidong and Changfeng soils,respectively.2.The effects of ammonium nitrogen fertilizer and polyaspartic acid on the growth and removal of Cd in soil were studied by soil culture experiment.The results showed that the combined treatment of nitrogen fertilizer and polyaspartic acid(NPASP)showed the same enhancement effect as NHA.NPASP significantly increased the biomass of Tagetes patula L.,which was 65.6% higher than CK.During the growth period of Tagetes patula L.,the combined treatment of nitrogen and polyaspartic acid significantly increased the content of Cd in Tagetes patula L.,which increased by 72.7% compared with CK treatment.In addition,NPASP treatment significantly increased the growth of the upper and root parts of the Tagetes patula L.Therefore,the biomass was increased,which was beneficial for Tagetes patula L.to absorb and enrich Cd in the soil.NPASP treatment increased the accumulation of Cd in the upper part of Tagetes patula L.meadow by 201% compared with the control.Therefore,the extraction efficiency of Cd under NPASP treatment was significantly higher than that under other treatments,and the extraction efficiency of Tagetes patula L.under NPASP treatment was the highest(28%).3.The results of hydroponic experiments showed that NPASP significantly increased root morphological parameters.Compared with CK treatment,total root length(68%),total surface area(91%),total root volume(106%),average root diameter(111%)and root tip number(49%)were increased.Polyaspartic acid(PASP)promotes lateral root formation by stimulating lateral root primordium formation.Compared with the control,the density of lateral root primordium under NPASP and PASP treatments increased by 213% and 126%,respectively.The growing lateral roots and root tips provide more channels for the plant to absorb cadmium ions.In this way,the absorption and enrichment of Cd by Tagetes patula L.were increased and the remediation efficiency was improved.In addition,NPASP treatment significantly improved the root activity and promoted the absorption of Cd by Tagetes patula L.roots.