Abundance And Diversity Of Ammonia-oxidizing Archaea And Bacteria In Rhizosphere Soil Of Three Plants In Ebinur Lake Wetland

Objective:Ebinur Lake Wetland,the most representative of temperate arid zone wetlands ecosystem in China,is a key role in regulating the climate and maintaining the regional ecological balance.As the first and rate-limiting step of nitrification,ammonia oxidation is carried out by ammonia-oxidizing bacteria(AOB)and ammonia oxidizing archaea(AOA).The aim of this study was to evaluate the relationship between the diversity and abundance of AOA and AOB in three constructive plants and soil environment factors in Ebinur Lake Wetland.Methods: Soil samples were collected from three rhizosphere and non-rhizosphere soil of plants(Halocnemum strobilaceum,Phragmites australis and Kareliniacaspia)in this wetland and were used to characterize diversity of AOB and AOB based on the ammonia monooxygenase(amoA)gene.By constructing clone library,q-PCR and RDA analysis to study the relationship between soil environment factors and the diversity and abundance of AOB and AOA in rhizosphere and non-rhizosphere soil in Ebinur Lake Wetland.Results: Soil physical and chemical factors showed that the pH in rhizosphere soil of Halocnemum strobilaceum(8.64),Phragmites australis(8.2)and Kareliniacaspia(8.61)were more than the non-rhizosphere soils’,indicating that the Ebinur Lake Wetland is alkaline soil;the soil moisture(SM): rhizosphere soil of Phragmites australis > rhizosphere soil of Halocnemum strobilaceum> rhizosphere flowerwood;the electrical conductivity(EC)in Halocnemum strobilaceum was highest than that in soil of Kareliniacaspia and Phragmites australis.The contents of organic matter(OM),total nitrogen(TN),nitrate nitrogen(NO3--N)and ammonium nitrogen(NH4+-N)were lower in different rhizosphere and non-rhizosphere soils,while the available phosphorus(AP)and available potassium(AK)was higher.The diversity indices of AOB,including Chao1 index,ACE index and Shannon-Wiener index,were higher than those of AOA in the rhizosphere soil of three plants.Phylogenetic analysis showed that AOA amoA sequences fell into two major clusters: Nitrosopumilus and Nitrososphaera clusters,and most of amoA sequences(92.92%)were affiliated to Nitrosopumilus cluster,indicating that Nitrosopumilus cluster were dominant in rhizosphere soil of three plants.AOB amoA gene fragments were grouped into Nitrosospira sp.and Nitrosomonas sp.,most of them(90.24%)fell within Nitrosomonas sp.,which included four clusters,such as Nitrosomonas oligotropha cluster,Nitrosomonas-like cluster,Nitrosomonas communis cluster and Nitrosomonas sp.Nm143 cluster.While only a few sequence(9.76%)were clustered with the Nitrosospira sp.,indicating that Nitrosomonas sp.may be more adaptable than Nitrosospira sp.in this area.The results of qPCR showed that the range of AOA abundance was 2.09 × 104-2.94 × 105 copies/g,and the highest abundance of AOA was in rhizosphere soil of Kareliniacaspia,which was 14.07 times of the abundance of AOA in rhizosphere soil of Halocnemum strobilaceum.The abundance of AOB was 2.91 × 105-1.05 × 106 copies/g soil,among which the abundance of AOB was the highest in rhizosphere soil of Phragmites australis.While the value of AOB/AOA was 2.09-29.92,which was lowest in rhizosphere soil of Kareliniacaspia and the highest was in rhizosphere soil of Phragmites australis.The abundance of the archaea ranged from 8.78 × 105-5.15 × 107 copies/g soil,while the range of bacteria was 4.74 × 104-4.8 × 108 copies/g soil.The lowest abundance of archaea and bacteria was found in the non-rhizosphere soil of Kareliniacaspia,while the highest abundance of archaea and bacteria was found in the rhizosphere soil of Halocnemum strobilaceum.RDA indicates that EC,OM,TN,NO3--N and NH4+-N were related to the diversity and abundance of ammonia oxidized microorganisms.Conclusion: Higher salinity,lower water content and less nutritious soil nutrient were found in soil of Ebinur Lake Wetland.AOA amoA sequences belong to Nitrosopumilus and Nitrososphaeraclusters.,AOB amoA belongs to Nitrosospira sp.and Nitrosomonas sp..The abundance of AOB was higher than the abundance of AOA.AOB might play a more crucial role in ammonia oxidation in Ebinur Lake Wetland based on the diversity and abundance of AOB.In addition,EC,OM,TN,NO3--N and NH4+-N might affect the structure and abundance of ammonia-oxidizing microorganisms.