Effects Of Intercropping System Between Mirabilis And Native Species On Soil Bacterial Characteristics Under Cadmium Stress

With the acceleration of urbanization and the rapid development of industrial and agricultural production,coupled with the toxicity and refractory properties of heavy metals,people are increasingly concerned about heavy metal pollution.According to the"National Soil Pollution Survey Bulletin",the excess rate of cadmium（Cd）in soil is 7%,ranking first among the eight inorganic pollutants.At present,there are many methods suitable for soil Cd pollution remediation,application is often limited by site conditions.Recently,people have begun to pay attention to microbial-phytoremediation method with strong adaptability,economic value and environmental friendliness.In this paper,the effects of Cd-enriched invasive plants Mirabilis and native cabbage on soil bacteria under Cd stress were studied after cropping and intercropping,and the degree of influence of Mirabilis on soil bacteria was revealed.In this paper,strains resistant to cadmium（Cd）,arsenic（As）,and lead（Pb）were isolated and purified from heavy metal-contaminated soil in the field,and the tolerance to single and composite heavy metals was studied,and then 16S r RNA sequencing was performed.Changes in bacterial communities in soils with different heavy metal pollution gradients were analyzed.Secondly,the field polluted soil,the campus self-contaminated Cd polluted soil and the campus unpolluted soil were used as pot experiments to study the changes of soil bacterial community in the cropping and intercropping of Mirabilis and cabbage.Finally,the soil contaminated with different Cd concentrations was matured and sterilized and then inoculated with heavy metal tolerant strains,which were used for single and intercropping of Mirabilis and cabbage.Effects of Mirabilis and cabbage under Cd Stress.The main findings of the paper are as follows:（1）In the field heavy metal-contaminated soils with different pollution gradients,the abundance and composition of soil bacterial communities were quite different.The results showed the main reasons for the formation of bacterial community differences were related to soil cation exchange capacity（CEC）,p H value,total zinc（Zn）,total As and available As concentrations.In addition,Bacillus pacificus MZ520364 was isolated and screened for tolerance to Cd,Pb and As.Under single heavy metal treatment,bacteria can tolerate 600 mg/L Cd²⁺,1000 mg/L Pb²⁺or 700 mg/L As³⁺.When Cd,Pb and As coexist,it grows best in the complex pollution system composed of 120 mg/L Cd²⁺,200 mg/L Pb²⁺and 150 mg/L As³⁺.The order of the effects of Cd,Pb and As on the growth of the strain was Cd>As>Pb.Compared with single heavy metal treatment,the combined heavy metal pollution was more toxic to the strain.The results revealed the ecological effects of soil physicochemical properties on bacterial community diversity and abundance,indicating that Bacillus pacificis MZ520364 could be used for the remediation of Cd-Pb-As complex contaminated soils.（2）Plant Mirabilis and cabbage on the field polluted soil,campus self-prepared Cd polluted soil,and campus unpolluted soil.The analysis of soil bacterial communities（CFU）in the rhizosphere and non-rhizosphere regions of three groups of soils with different planting methods showed soil bacterial CFU was the least in the field soil,and bacterial CFU in the uncontaminated Cd soil was the most,which was closely related to the degree of soil Cd pollution.related.Compared with the intercropping of Mirabilis,the difference of bacterial CFU wasn’t significant,and the bacterial CFU in the case of green crop was significantly smaller than that in the case of intercropping.For Mirabilis and cabbage,the activities of invertase and urease in the non-rhizosphere zone of the three groups of soil were significantly higher than those in the rhizosphere zone,which was related to the influence of soil bacterial life activities on soil carbon metabolism and nitrogen content.The results revealed the effects of different Cd-contaminated soils and the planting methods of Mirabilis on the CFU of soil bacteria in the rhizosphere and non-rhizosphere zones,and the changes of soil sucrase and urease.（3）With the continuous increase of soil Cd concentration,the growth conditions of Mirabilis and Chinese cabbage gradually deteriorated.Compared with uninoculated bacteria,after inoculation with exogenous bacteria,the growth,shoot and root bioconcentration factor（BCF）of Mirabilis and cabbage were significantly improved.The enrichment effect of Cd was improved.The Cd enrichment effect of cabbage is better than that of Mirabilis.In practical applications,Bacillus pacificis should be inoculated into Mirabilis alone to achieve the purpose of Cd pollution remediation in soil.In summary,under Cd stress,the intercropping of Mirabilis and cabbage would negatively affect the growth of bacteria in the soil rhizosphere zone and non-rhizosphere zone and the content of soil enzymes,the bacteria in the rhizosphere zone were more affected than those in the non-rhizosphere zone;The resistant strain Bacillus pacificus MZ520364 isolated and screened from field soil was inoculated into Cd-contaminated soil.Phyto-microbial joint remediation of cadmium-contaminated soils.