Changes Of Soil Microbial Community Structure In Different Gradients Of Heavy Metal-Contaminated In Paddy Soils

As an important component of soil,soil microorganism is more sensitive to the change of soil environmental quality than that of plant,and plays an important role in maintaining the structure and stability of ecosystem.In this study,our objective was to advance the understanding of the indigenous microbial communities of heavy metal-contaminated rice paddy soil at difference levels in the area of South Jiangsu.We analyzed the bacterial and fungal abundance and community structure of heavy metal contaminated paddy soils at different gradients,and found that heavy metal pollution at difference levels had a significant different effect on soil microbial community structure in rice season.The main conclusions were as follow:1.Soil bacteria abundance in different gradients of heavy metal pollution in the paddy soil had no significant difference,but there are significant differences in bacterial community structure diversity,and with the increase of pollution degree,the diversity index decreased amplitude increases,the bacterial diversity index of high concentration heavy metal contamination samples is the smallest.There were significant differences in soil fungal abundance in heavy metal contaminated samples.Compared with the control,the fungal abundance of heavy metals contaminated with different levels decreased significantly.The richness index of fungi varied significantly in different gradients of heavy metal pollution,in effect,compared with the control,the richness index of middle and low concentration heavy metal pollution samples decreased significantly,and with the decrease of heavy metal pollution,the richness index decreased,which indicated that the heavy metal pollution had a significant effect on the fungal community structure,but it was not a simple linear relationship.2.By Principal coordinate analysis,we found that the effect of heavy metal pollution at difference gradients on microbial community structure was different and the difference was significantly.The first components accounted for 40.30%and the second components for 23.27%on the bacterial community structure.The contribution rate of PC1 influencing factors to fungal diversity was 35.96%,and the PC2 was 21.48%.The first two axes of the PCoA explained 63.57%of the initial data variability on the bacterial community structure and explained 57.44%of the initial data variability on the fungal community structure.The bacterial and fungal communities in the samples with similar levels of heavy metal contamination were similar,and with the increase of heavy metal pollution,the bacterial and fungal community structure was further differentiated.3.After RDA and NMDS analysis,we found that different heavy metals have different effects on microbial community structure.Heavy metal Pb/Cd/Cu/Zn in the environment had a synergistic and negative correlation on the bacteria in the soil.The effects of Pb and Cu pollution on soil fungal community structure were very significant,in addition Pb and Cu were synergistic,Pb and Cd/Zn is antagonistic.There were significant differences in community composition of heavy metal contaminated samples at different concentrations.4.Through the analysis of the relative abundance of bacteria in the genus classification level,we found,the relative abundance of Thiobacillus/Anaerolinea/Planctomyces in heavy metal contaminated samples had a significant increase trend,the relative abundance of Thiobacillus along with the increase of pollution degree increased,the highest increase of 7 times;GOUTA19,the relative abundance of Methylibium/4-29/Phenylobacterium and other sensitive bacteria in heavy metal pollution samples decreased significantly,the relative abundance of GOUTA19 is reduced up to 80.53%,4-29 maximum reduction of 60.97%,Methylibium relative abundance decreased by 57.14%.The relative abundance of fungi of the genus analysis showed that heavy metal pollution will significantly reduce the heavy metal sensitive fungi,such as Mortierella belongs to the highest abundance decreased 87.50%,Trichoderma is reduced up to 99.46%,from the shell bacteria and the mushroom genus is reduced up to 100%,while the relative abundance of fungi resistance will increase,such as relative abundance paraglomus the highest increase of 98 times,four Cladosporium had the highest increase of 56 times,the highest root olpidiopsis increased 2.62 times.In summary,heavy metal pollution can significantly change the community structure of soil microorganisms and the effect of heavy metal pollution at different gradients was different.Improving the microbe on heavy metals in the environment pollution stress adaptability,so as to maintain the balance and stability of ecological system,therefore have a certain impact on soil ecological function,such as soil organic carbon sequestration.