Characteristics Of Profile Soil Microbial Community Structure And Function In Poyang Lake Wetland

Poyang Lake wetlands is the largest natural freshwater wetland of China,with seasonal water level dynamic,diverse soil types and abundant natural resources.With the continuous improvement of the understanding about the function of wetland,the wetland ecosystem of Poyang Lake began to attract scholar’s attention.The study of wetland soil profile suggested that the deep soil may contain a large amount of microbial resources,which plays an important role in the transformation and energy cycling of wetland ecosystem.However,when it comes to vertical distribution of the microbial community structure,function,metabolic activity and its major influence factors,we still need systematic research of lake wetlands.Therefore,this study took Poyang Lake wetland soil as the research object,and the soil samples were selected in three typical areas such as Bang Lake（BH）,Changhuchi（CHC）,Nanjiashan（East Lake）（NJS）.We collected profile soil with five depths: 0-20 cm,20-40 cm,40-60 cm,60-80 cm,80-100 cm.We adopted methods such as the 16 S rRNA high throughput sequencing,qPCR,Biolog-ECO plate to determine the soil physico-chemical paremeters,extracellular enzymes activities,microbial carbon source metabolic activities,microbial biomass,bacterial abundance and bacterial community sturucture.To clarify the spatial changes of microbial community structure and metabolic function in the Poyang Lake wetland,especially the characteristics of the depth along the profile soil,and provide a new way for the microbial community to suggest the mechanism of soil evolution.The experimental results were as followed:（1）The main dominant bacteria at phylum level in Poyang Lake wetland was Chloroflexi（30.83%）,followed by Proteodacteria（21.37%）and Acidobacteria（18.85%）.At the lower classification level-family level,the main dominant species is Anaerolineaceae（17.49%）,followed by Acidobacteriaceae_Subgroup1（9.36%）and HSB_OF53-F07（8.00%）.At the same time,the soil bacterial abundance（1.60×108-7.49×1010 copies/g）and Chao1 index（663-2664）in Poyang Lake wetland were also higher than those in other freshwater wetland ecosystems.METAGENassist was used to predict metabolic function based on bacterial communities.The results showed that the metabolic function of the bacterial community in the surface soil mainly included Sulfate reducer（41.9%）,Ammonia oxidizer（35.8%）,Nitrite reducer（3.3%）,Dehalogenation（27.7%）,Sulfide oxidizer（25.8%）,Xylan degrader（20.1%）,Nitrogen fixation（11.0%）;The metabolic function of bacterial communities in deep soil mainly included Ammonia oxidizer（37.7%）,Sulfate reducer（34.3%）,Nitrite reducer（27.8%）,Sulfide oxidizer（25.7%）,Dehalogenation（22.9%）,Methane oxidation（20.0%）,Xylan degrader（18.7%）.（2）The soil bacterial abundance and community structure of Poyang Lake wetland soil were significantly changed along the depth of soil profile,and the difference was mainly between the surface（0-20cm）soil and the deep（20-100cm）soil.In the composition of the main bacterial communities,the relative abundance of the Chloroflexi,Proteodacteria,Acidobacteria was significantly different in wetland soil profile depth.On the metabolic function of bacterial communities,Denitrification（7.0%）and Stores polyhydroxybutyrate（0.02%）were only present in the surface soil.Naphthalene degrading（0.9%）and Selenate reduceer function（0.04%）were only present in deep soil.It is worth noting that the Methane oxidation function（20.00%）in the deep soil is significantly higher than that in the surface soil（0.08%）.Further studies have found that although there are significant differences in soil bacterial community structure between different plots,the difference is far less significant than the difference in depth.（3）The soil microbial function（microbial biomass,extracellular enzyme activity,carbon source metabolism）of Poyang Lake wetland was significantly affected by soil depth.The microbial activity of the surface soil（0-20cm）was the highest,and the soil microbial activity was stable after the soil depth reached 60 cm.But the deep soil is still carried out by the micro-organisms involved in the complex metabolic activity and can not be ignored.In addition,only microbial carbon source metabolic activity showed significant differences between plots.Soil microbial biomass,extracellular enzyme activity did not change with the difference of plots.The results show that soil microbes as a sensitive indicator of environmental changes,the community structure’s changing will take precedence over some changes in metabolic function,in order to cope with changes in the external environment.（4）The correlation analysis and RDA analysis showed that the soil microbial functional characteristics and bacterial community structure of Poyang Lake wetland were mainly affected by soil organic matter（AFDM）and nutrient elements（TOC,TN）.In addition,soil water content（SM）is also one of the factors that affect soil microbial functional characteristics and community structure.AFDM,TOC and TN along the soil depth were significantly different,leading to Poyang Lake wetland soil microbial functional activity and bacterial community structure with the depth of soil profile changes;The difference of soil SM between different plots resulted in the change of soil microbial carbon source metabolic activity and bacterial community structure with different plots.（5）Through the correlation analysis and redundancy analysis,it was found that Bradyrhizobiaceae 、4-29、Xanthobacteraceae is closely related to the activity of Bxyl、Pero、Bglu 和 Phos.The Spirochaetaceae was related to the activity of NAG.Acidothermaceae,1921-3,HSB_OF53-F07,Cystobacteraceae and sh765B-TzT-35 are the most important species that affect the metabolism of carbon source.In conclusion,the soil properties,soil bacterial community structure,bacterial abundance and functional characteristics of Poyang Lake wetland showed significant differences with soil profile,but the difference was not obvious at horizontal distance.The microbial function of surface soil was higher than that of the deep soil（20-100cm）,but the deep soil（even to 100 cm depth）still had complex bacterial community composition and higher metabolic activity.This is not consistent with the vertical distribution of soil microbes in other ecosystems.This suggests that in wetland ecosystems,different depths of soil microbes have different community composition and metabolic functions.The role of deep soil microbes in soil evolution is worthy of our attention.The results of this study reveal the spatial distribution of soil microbes in Poyang Lake wetland,and deepen our understanding of wetland ecosystem.Comprehensive and systematic understanding of wetland ecosystem is an important scientific basis for wetland environmental management,resource protection and sustainable development.Features of this project: The spatial distribution of soil microbial community structure and functional characteristics in Poyang Lake wetland was systematically studied for the first time.To provide a reference for predicting the evolution and functional activity of microorganisms in Poyang Lake wetland ecosystem;Early using the METAGENassist analysis,which can associated the high-throughput sequencing results of 16 S rRNA with the community metabolic function.The conclusion of this study was helpful to our further understanding of the functional diversity and importance of soil microbes in wetlands along the vertical depth.