Study On The Effect And Mechanism Of Cd Enrichment Under The Condition Of Intercropping Of Mazie And Hyperaccumulation

The area of cultivated land polluted by industry and agriculture in China is 1×10¹² m²,Cd,one of the main heavy metal pollution elements,is relatively persistent in the soil.At present,the intercropping technology of maize and hyperaccumulator has attracted much attention because of its economy,green and environmental protection.However,the related technology research is less,and it is not systematic,so it can not be well applied and popularized.In order to provide a theoretical basis for the remediation of maize and hyperaccumulator plants in farmland,the enrichment characteristics of maize and hyperaccumulator in different ecological niches and the mechanism of root interaction on the competitive absorption of heavy metal cadmium were studied.The main results and conclusions are as follows:?1?Through the field plot experiment,there are 7 planting patterns,including monoculture of maize?CK1?,monoculture of S.nigrum?CK2?,wide-narrow-row of maize and single-row S.nigrum intercropped between wide rows?T1?,wide-narrow-row of maize and double-row interlaced S.nigrum intercropped between wide rows?T2?,equidistant single-row maize and single-row S.nigrum intercropped?T3?,equidistant single-row maize and double-row interlaced S.nigrum intercropped?T4?,maize and S.nigrum intercropped with equal 4 rows?T5?.The changes of biomass land equivalent ratio,Cd content,total Cd extraction,concentration and transfer coefficient,pH and available Cd content in rhizosphere soil of maize and S.nigrum were studied in intercropping modes.The results showed that the land equivalent ratio of the five intercropping modes was greater than 1.Compared with CK1,T3 intercropping increased maize yield by 15.6%,T1,T4,T5 intercropping decreased maize yield by less than 10%,T2 intercropping mode decreased maize yield by 16.8%;compared with CK2,five intercropping modes showed total biomass of per plant.no significant change.The five intercropping modes did not significantly change the Cd content,bioaccumulation coefficient and transport coefficient of maize and S.nigrum,but significantly increased the total Cd extraction per unit area,of which T4 intercropping mode was the highest.In addition to T5,the other four intercropping modes significantly reduced the pH of S.nigrum and maize rhizosphere soil,increased the Cd content of S.nigrum rhizosphere soil,but decreased the Cd content of maize rhizosphere soil.This indicated that the growth of maize and S.nigrum was promoted by interspecies,The intercropping modes of T1,T3,T4 and T5 could not only ensure the stable yield of maize,but also significantly improve the efficiency of restoration,and realize the purpose of restoration while producing,among which T4 intercropping mode was the best.In addition,the seeds of S.nigrum in Shenyang area are not adaptable in Hunan Province,so it is suggested to choose local S.nigrum as intercropping for restoration.?2?Pot experiments were carried out to explore the rhizosphere interaction were divided into three types:solid barrier?SB?,mesh barrier?MB?and no barrier?NB?.Cd content of maize roots in the three models of rhizosphere interaction significantly reduced.In 16SrRNA Gene Sequencing,the composition of rhizosphere dominant bacterial community of maize and T.patula was similar at the level of phylum classification,which Proteobacteria,Chioroflexi,Acidobacteria and Actinobacteria had higher relative abundance,but the relative abundance of bacterial community was different,which indicated the influence of different intercropping patterns.PCoA showed that the composition of bacterial community had a certain migration at the level of OUT.In the analysis of the differences between groups,it was found that the relative content of allorhizobium neorhizobium parrhizobium Rhizobium decreased significantly,which could inhibit the entry of Cd into maize roots and reduce the content of Cd transferred to the upper part of the ground.Methylobacillus could promote the growth of plant stem and leaf,increase the tolerance of heavy metals in plant rhizosphere,and reduce the absorption of heavy metals by reducing the effective content of heavy metals in soil.?3?Using LC-MS analysis method,27 kinds of metabolites were identified as potential biomarkers in maize rhizosphere and 31 kinds of metabolites were identified as potential biomarkers in T.patula rhizosphere.Amino acids and polysaccharides played an important role in heavy metal adsorption.Organic acids secreted by plant roots can resist environmental toxicity and improve the resistance of plants to heavy metals.Arginine biosynthesis in amino acid metabolism and pentose glucuronic acid transformation in carbohydrate metabolism played an important role in plant resistance to heavy metal stress.Under Cd stress,the metabolites produced by the two metabolic pathways contain a large number of amino and hydroxy functional groups,which can complex with Cd and reduce the transfer of Cd from the maize root to the above ground.Through these two metabolic pathways,the secretion and the process of their own life activities were regulated to actively resist the Cd toxicity.The mechanism of Cd resistance in maize roots was mainly through the metabolism of sugar and amino acids,promoting the cycle of tricarboxylic acid,then affecting various metabolic pathways in maize roots.