Effects Of Earthworm Behavior On Soil Quality And Growth Of Arabidopsis Thaliana Under Cadmium Stress

With the rapid development of global industry,heavy metal pollution is becoming more and more serious around the world,and it has gradually become a global environmental problem.Heavy metals further affect soil quality and affect plant growth by affecting soil plants,animals,microorganisms and their interrelationships.Soil animals,including earthworms,are an important part of terrestrial ecosystems.However,the effects of heavy metals on soil quality and plant productivity in composite ecosystems are relatively scarce under the mediation of earthworms.This paper takes the heavy metal cadmium as the research object,discusses the effect of cadmium(0,0.3,1.0,3.0 mg/kg)on the survival of earthworms and the physical and chemical properties of the soil,and comparatively analyzes the relationship between the microbial diversity and abundance of earthworm intestines and soil microorganisms To further explore the effect of earthworm-mediated cadmium stress on the growth of Arabidopsis thaliana.Experimental results show that:(1)The survival rate of earthworms under cadmium stress is between 70% and 80%,and there is no significant difference between the treatments of different concentrations.The addition of cadmium significantly affected the abundance and diversity of intestinal microbes in earthworms.As the concentration of cadmium treatment increased,the shannon index and simpson index of earthworm intestinal microbes gradually decreased,and the simpson index was significantly different from the control.At the phylum level,about 90% of the microorganisms belong to ten dominant phylums,among which Actinobacteria has the highest dominance.Compared with the control group,the relative abundance of Pachymena and Proteobacteria in soil samples with a concentration of 3.0 mg/kg increased by 41.3% and 16.7%,respectively,while the relative abundance of Actinomycetes decreased by 17.2%.(2)Under earthworm-mediated heavy metal cadmium treatment,the soil pH value was significantly lower than that of the control.The contents of total nitrogen,alkali-decomposed nitrogen,total potassium,and organic matter in the soil showed a trend of increasing first and then decreasing,and were significantly different from the control.However,the changes in the content of total phosphorus and available potassium in the soil were inconsistent,all of which were in the treatment group content of 3.0 mg/kg reach the highest.However,the change of total phosphorus was not significant,and the content of available potassium was significantly higher than that of other groups.Cadmium stress reduces the abundance and diversity of microorganisms in the soil.The chao index of soil microbial samples decreased compared with before treatment,that is,the abundance of soil microbes decreased.The shannon index gradually decreased with the increase of cadmium treatment concentration,and gradually increased with the extension of the treatment time;soil microorganisms Proteobacteria(accounted for 25%-46%),Phytophthora(accounted for 6%-33%),Actinomycetes(accounting for 11%-28%)is the highest relative abundance,while cadmium stress increases the relative abundance of Actinomycetes and Proteobacteria in the soil.Compared with soil microorganisms,the relative abundance of Firmicutes and Actinomycetes in the intestinal microorganisms of earthworms increased significantly.(3)Heavy metal pollution caused the dwarfing of Arabidopsis plants.Compared with the control,the length of the main stem of Arabidopsis thaliana treated with the heavy metal cadmium content of 0.3 mg/kg,1 mg/kg,and 3 mg/kg decreased by 3.0%,3.9%,and 6.4%,respectively.Cadmium stress increased the number of branches of Arabidopsis thaliana,and the number of branches with a heavy metal cadmium content of 1.0 mg/kg increased by 56%.With the increase of pollution concentration,Arabidopsis thaliana reduces the energy input of leaves and increases the energy input of stems and roots,which is beneficial to the absorption of nutrients by plants in adversity.The addition of cadmium significantly affected the growth cycle of Arabidopsis thaliana,which enabled Arabidopsis to enter reproductive growth in advance.Compared with the control,the initial flowering period of the highest concentration treatment was advanced by 12.9%,shortening the time from flowering to fruit pod maturity by 21.0%,and increasing the proportion of energy for reproductive growth to 44.8% within the same growth time.This resulted in more progeny,but the quality of the progeny decreased significantly,and the thousand-grain weight of the seeds dropped by 3.8%.The comprehensive study found that cadmium pollution reduced the abundance of earthworm intestinal microbes and soil microbes and increased its diversity,and increased the relative abundance of cadmium-resistant microbes in the microbial community.Under the treatment of lower concentration of cadmium,the content of soil nutrients increased with the increase of soil cadmium concentration,but it still showed a trend of increasing first and then decreasing,but it was still higher than that of the control group.The increase of nutrients and the decrease of the effectiveness of heavy metal cadmium have improved soil quality.The total biomass of the plant increased,and Arabidopsis thaliana entered the reproductive growth ahead of time,thereby obtaining more offspring,but the quality of the offspring declined.Under the mediation of earthworms,the low concentration of cadmium has promoted the growth of contemporary plants,but reduced the quality of offspring,which is not conducive to the long-term survival and reproduction of plants.To explore the impact of heavy metals on the soil ecosystem consisting of soil-earthworm-microorganism-plant.The results of this study provide a theoretical reference for the biological diagnosis and risk assessment of heavy metal contaminated soil.