Arsenic Stressed Responses Of Maize And Its Intercropping With Pteris Vittata For Remediation Of Arsenic-contaminated Soil

Pteris vittata,an arsenic（As）hyperaccumulator,is widely used in phytoremediation of As polluted soils.Intercropping of Pteris vittata with crops is a key method to realize the"production while remediation"of contaminated farmlands.However,the soil As remediation effects and the related mechanisms of P.vittata intercropping with different crops are not well understood.Based on the screening of maize（Zea mays L.）varieties with different ability of arsenic absorption and utilization,we studied the physiological and molecular mechanisms of genotypic maize under arsenic stress,and by use of soil microplot experiment and root zone separation technique,we further explored the effects of intercropping modes of P.vittata with maize,ramie（Boehmeria nivea（L.）Gaudich.）and castor（Ricinus communis L.）on the growth of P.vittata and three crops,the As and nutrient uptake and accumulation,the antioxidant enzyme response,the soil As fractionation and microbial diversity as well as the effects and mechanisms of the remediation of As contaminated soil.The main research results are as follows:1.Under the solution culture conditions,the genotype differences of 20 maize varieties to arsenic stress were studied to screen maize genotype varieties.The results showed that under arsenic stress,the growth index parameters of maize were greatly varied,the treatments/CK ratios of germination potential,germination rate,root length,shoot length,dry weight of maize seeds were 0.58-1.18,0.61-1.18,0.49-1.04,0.72-1.12 and 0.55-2.83,respectively.Arsenic transport coefficient of seedling stage maize were 0.02-0.07.Principal component analysis and cluster analysis were carried out with 12 indicators,and two tolerant and five sensitive cultivars were thus selected,among which Kangnongyu 999 was the most As tolerant and Sanbei 89 was the most As sensitive.The genotype difference of arsenic sensitive and tolerant varieties in antioxidant reactions under arsenic stress were analyzed.The results showed that,the activities of CAT,POD and SOD of tolerant variety Kangnongyu 999 treated with arsenic were less than those of the CK.The contents of MDA,GSH and ASA were all higher than those of the CK.However,the activities of SOD,CAT and POD and the contents of GSH and ASA of sensitive variety Sanbei 89 treated with arsenic were higher than those of CK,but the content of MDA was only 0.5 times of that of CK.2.Transcriptome analysis of maize under arsenic stress showed that,in five detected arsenic-resistant transcripts,compared with As tolerant variety Kangnongyu999,four detected arsenic-resistant transcripts in As sensitive variety Sanbei 89increased significantly,only one Ars B transcripts slightly decreased.GO function analysis found that there were functional groups closely related to arsenic stress,such as metabolic process,antioxidant activity,detoxification and cell killing.Gene annotation was carried out for the functional groups of metabolic process and detoxification.It was found that peroxidase,glutathione transferase,asparagine synthetase,catalase and other genes had significant differences in the gene number of the sensitive maize variety Sanbei 89 and the tolerant maize variety Kangnongyu 999(P_adjust<0.05).The genes described as probable peptide/nitrate transporter,ARM repeat superfamily protein,ADPATP carrier protein mitochondrial,phosphoenolpyruvate/phosphate translocator chloroplastic functions played important role in the transport activity functional group.The enrichment results of KEGG pathway involved many metabolic pathways,including carbohydrate metabolism,amino acid metabolism,energy metabolism,etc.This indicated that the physiological parameters and gene expression of different maize genotypes under arsenic stress were significantly different.3.By use of soil microplot experiment and root zone separation technique,the intercropping modes of P.vittata with maize,ramie and castor were designed to investigate effects and mechanisms of remediation of soil arsenic pollution.The results showed that,the intercropping increased As content of P.vittata by3.1%-25.3%,decreased As content of maize grains and leaves of ramie and castor by70.9%-95.6%,29.2%-32.0%and 18.8%-32.0%,respectively,indicating higher remediation efficiency by P.vittata-crop intercropping.The intercropping of Pteris vittata with maize,ramie and castor were conducive to increase the total nutrient contents（NPK）of the three crops,promoted the plant biomass and the transpiration rate,and decreased oxidative stress of As.Arsenic fractionation analysis of rhizosphere soil under intercropping conditions showed that,the proportion of iron-bound As was enhanced in P.vittata rhizosphere soil but decreased in three crop rhizosphere soils.Analysis also showed that the intercropping increased soil p H value and available As content in P.vittata rhizosphere.4.The analysis of soil microbial diversity showed that,the coverage of 13intercropping modes was higher than 98.5%.There were 624 OTUs in five Pteris vittata-maize intercropping treatments.PCA analysis of the first and second principal components explained 90.35%and 4.6%of the differences in microbial composition of rhizosphere soil,respectively.There were 727 OTUs in five Pteris vittata-ramie intercropping treatments.PCA analysis of the first and second principal components explained 48.45%and 30.05%of the differences in microbial composition of rhizosphere soil,respectively.There were 745 OTUs in five Pteris vittata-castor intercropping treatments.PCA analysis of the first and second principal components explained 59.38%and 26.52%of the differences in microbial composition of rhizosphere soil,respectively.Intercropping improved soil microbial composition,increased the abundance of proteobacteria and actinobacteria,and decreased the abundance of chloroflexi.