Effects Of Mn(Ⅱ) Addition On The Structure And Function Of Bacterial Community In Paddy Soils During Dry-Wet Alternation

Manganese is a metal element with high content in the earth’s crust.It is abundant in paddy soils and is a component of the redox system of paddy soils.Its existence is affected by the water content of paddy soil.Manganese is a trace element necessary for the growth of organisms.It has a wide valence distribution.There are compounds from-3 to+7,but there are only three bioactive states that is Mn(Ⅱ/Ⅲ/Ⅳ),the content of Mn(Ⅱ)is increased in the flooded environment,and it is the only form have toxic for organisms at high concentrations.As a sensitive biological indicator,the content of Mn(Ⅱ)affects the microbial community structure.In the draining environment,the form of manganese will change,and this process is mainly carried out by microorganisms.This experiment is carried out by indoor simulation.Use fluorescence quantitative technique to measure the change of 16S rRNA gene copy number after Mn(Ⅱ)addition;IonS5TMXL high-throughput sequencing technology was used to analyze the changes of soil bacterial community structure after Mn(Ⅱ)addition.The content of manganese in various forms under redox conditions after Mn(Ⅱ)addition was determined by BCR sequential extraction method.It can provide an important reference for the effect of various forms of manganese on microbial effects.The addition of Mn(Ⅱ)had no significant effect on the copies number of 16S rRNA gene in flooded environment.The environmental factors that had significant effects on copies number were soil texture,soil organic carbon and RES.Mn,respectively.The other forms of manganese had no significant effect on copies number.The high Mn(Ⅱ)addition in the draining environment significantly reduced the 16S rRNA gene copies number of the two paddy soils.Soil texture was also one of the main factors affecting the copies number,and each form of manganese had a significant effect on the 16S rRNA gene copies number.The addition of Mn(Ⅱ)in the flooded environment significantly increased the microbial community Shannon index diversity of the Sand,while the microbial community Shannon index diversity in the drained environment was significantly reduced.The diversity and richness index of Loam without significant effect with added of Mn(Ⅱ)in the two environments.The weight unifrac PCoA analysis based on sequence level shows that the Sand can be clearly distinguished between the three treatments under two environmental conditions,however,for Loam treatment samples,LL and LH could not be distinguished clearly in the flooded environment,and the three treatments could be clearly distinguished in the draining environment.The CCA results analysis found that in terms of sand treatment,all forms of manganese except RES.Mn in the flooded environment had a significant impact on the OTU distribution,in the draining environment,the corresponding form of manganese has a significant effect on the OTU distribution.For loam,Mn(Ⅱ)addition treatment had no significant effect on OTU distribution in flooded environment.RES.Mn had a significant effect on OTU distribution in drained environment,and other forms of manganese had a significant effect on OTU distribution.High-throughput sequencing of 16S rRNA in flooded paddy soil showed that there were 9 and 8 dominant phyla(>1%)in Sand and Loam,respectively;based on Lefse analysis and dominant genus(>1%)significant analysis,we find that the relative abundance of different levels of Mn(Ⅱ)added to Sand soil such as Verrucomicrobiae,Holophagales,Holophagaceae and Fonticella,Bryobacter,unidentified_A cidobacteria,Candidatus_Solibacter and Geothrix was significantly changed.Significant changes in the Loam were Haliangium,unidentified_Gammaproteobacteria and Geobacter.Base on PICTRUSt function predicts we find that the addition of Mn(Ⅱ)in sand significantly inhibits the nitrogen-fixed metabolic pathway and significantly promotes the nitrate reduction pathway and the sulfate reduction pathway;however,the addition of Mn(Ⅱ)to Loam has no significant effect on the carbon,nitrogen and sulfur metabolic pathways..The high-throughput sequencing of 16S rRNA in drained paddy soil showed that there were 13 identical dominant phyla and 11 identical dominant genera in the two soils,and there were 4 unique dominant genera in Sandy and Loam soil.The difference analysis showed that in Sand soil the abundances of Thiobacillus,Sideroxydaus,Pseudarthrobacter,Bradyrhizobium and Arthrobacter was significantly increased with high concentration of Mn(Ⅱ),while the abundance of Haliangium and Bryobacter showed SCK>SL>SH.For Loam soil,the abundance of Candidatus_Nitrosotalea and Desulfobacca was LCK<LL>LH,while the abundance of Bradyrhizobium was LCK>LL>LH.Base on PICTRUSt function predicts we find that the addition of Mn(Ⅱ)in Sand can promotes nitrate reduction pathway,denitrification pathway,nitrate respiratory pathway,Calvin circulation pathway and sulfate reduction pathway.Adding Mn(Ⅱ)in Loam can promote nitrate reduction pathway and part of Calvin cycle,but the complete nitrification pathway and sulfate reduction pathway were inhibited.