Dynamic Changes Of Soil Bacterial Community Structure And Diversity Under Four Re-vegetated Plant Species In The Riparian Zone Of The Three Gorges Reservoir Area

After the completion of the Three Gorges Dam,the hydrological control mode of"storage in winter and drainage in summer"has been formed.The long-term flooding has seriously degraded the original terrestrial ecosystem,causing serious problems such as soil erosion,habitat loss,biodiversity decline and environmental pollution in the fluctuation zone.The planting of suitable plants is of great significance to vegetation restoration in the water-level-fluctuation zone of the Three Gorges Reservoir Area.Cynodon dactylon,Hemarthria altissima,Taxodium distichum,and Salix matsudana are the most suitable species for vegetation restoration in the water-level-falling zone of the Three Gorges Reservoir area.Each of the four species has developed root system,fast growth,and flood and drought tolerant ability,and the like,which is of great significance to maintain the soil and water in the riparian zone.In order to further understand the adaptation of artificially restored vegetation to the adverse environment in the riparian zone,this paper studied the soils of artificially restored vegetation with four dominant species in the riparian zone through exploring the relationship between plant rhizosphere,soil and microorganism,in combination with 16S rDNA high-throughput sequencing technology.The sampling time was in May,July and September in 2020.The indices measured included soil physicochemical properties,enzyme activity and soil bacterial diversity.Meanwhile,PICRUSt2 was also used to predict soil bacterial function.The results showed that:(1)Soil physicochemical and enzyme activities of the four suitable plants had a certain time variation.The soil pH value in different period ranged from 6.74-7.55,and the soil moisture content ranged from 15%to 22%.The temporal heterogeneity of soil physicochemistry of various species was mainly reflected in pH(pH value),NO3~--N(nitrate-nitrogen),TN(total nitrogen),TK(total potassium),OM(organic matter).The indexes of TC(total carbon),TN,OM,NO3~--N,AP(available phosphorus),NH4~+-N(ammonium nitrogen)were enriched in different degree in the rhizosphere,but the changes of nutrient contents were not consistent between the rhizosphere and non-rhizosphere.The activities of soil enzymes were significantly enriched in the rhizosphere.The OM,TC,TN,NH4~+-N,NO3~--N and AP had the significant relationship with the activities of soil enzymes at different sampling stage related to the four suitable plants.(2)There were abundant microbial resources in the soils of the four vegetation.A total of 31086 OTUs belonging to 1236 genera,728 families,223 classes,464 orders,223 class and 64 phyla were identified by 16S rDNA high-throughput sequencing.Proteobacteria and Acidobacteria were the dominant phyla in all soil samplings,and the sum of average relative abundance was more than 60%.Alphaproteobacteria,Betaproteobacteria,Acidobacteria-6,Deltaproteobacteria and Gammaproteobacteria were the dominant class in all soil samples,accounting for about 52%of the total in all soil samples.The composition of soil bacterial communities under different vegetation was similar,but the relative abundance of soil samples at phylum level had a certain time difference,while there was no obvious time difference in the class level.(3)The change of soil bacterial diversity showed a certain dynamic pattern,but the variation trend was not consistent under different vegetation types.The temporal variation trend ofαdiversity of rhizosphere bacteria community was different between herbs and woody species,and theαdiversity of rhizosphere soil of the two herbs was T3>T2>T1,and theαdiversity index of the two woody rhizosphere bacteria was T1>T2>T3.Theαdiversity of non-rhizosphere bacterial community showed no obvious change trend across different periods.The changes of soil ORP(oxidation-reduction potential),OM,AP and soil urease across experimental period had significant effects on bacterial community structure.(4)A total of 45 sub-functional groups from six metabolic pathways were found in the soil bacteria related to four vegetation.Among them,metabolic,genetic and environmental information processing pathways were the most common in the primary functional layer,accounting for 73%of all functions.In the secondary functional layer,the metabolic pathways related to carbon,nitrogen and phosphorus mainly included amino acid metabolism,carbohydrate metabolism,lipid compound metabolism and energy metabolism,and the relative abundance of each metabolic function had a certain time difference in different periods.(5)The soil nutrient status of different vegetation types was different,but there was no obvious change trend among different vegetation types.The soil enzymes of the two herbaceous vegetation had stronger rhizosphere effect,and theα-diversity index of soil bacteria was higher in the herbaceous vegetation than in the woody vegetation,which showed a better adaptability to the environment in the riparian zone of the Three Gorges Reservoir area.