Study On The Community Structure And Abundance Of Functional Bacteria Involved In Nitrogen Cycling Of The Rhizosphere In Emergent Plants

The wetland is one of the most important ecosystem in the world,it can produce huge impact to the maintain of global ecosystem balance and human's production activities due to it's strong controlling ability.Nitrogen is an element which directly influence the primary productivity of wetland.Nitrogen-cycling is one of the most important ecological function which is an indispensable part of biosphere's material energy cycle.Bacteria plays an important role in nitrogen-cycle,many key reactions of nitrogen-cycle must be catalyzed by it.Plant roots create a specific microenvironment which suitable for the growth of bacteria due to rhizosphere effect.The number of rhizosphere bacteria and metabolic activity is far higher than that of non-rhizosphere soil.There are lots of aquatic plants growing in natural and artificial wetland,the plant-bacteria system can produce a huge impact on the nitrogen-cycle of wetlands.The study on the community structure and total number of the rhizosphere bacteria of emergent plants,the research on abundance of important functional bacteria involved in nitrogen-cycle,which has huge significance on the restoration and purification of wetland ecosystem.In this research,we took pot experiment to cultivate 4 widely distributed emergent plants Phragmites australis,Typha orientalis,Zizania caduciflora and Scirpus validus.Then the Illumina Miseq sequencing was used to analyse the community structure of rhizosphere bacteria of these 4 plants and the Real Time quantitative PCR was used to measure the quantity of total rhizosphere bacteria and the functional genes involved in nitrogen-cycling including nifH,amoA,nirS,nirK,nosZ and amxC.The Illumina Miseq sequencing platform produced 586841 initial sequences,then we get 460970 high quality sequences according date dealing,and each sample gets an average of 30731.These sequences are divided into 26 phylum,which including Proteobacteria,Firmicutes,Chloroflexi,Bacteroidetes,Acidobacteria,Cyanobacteria,Planctomycetes,Actinobacteria,Nitrospirae,Verrucomicrobia,Gemmatimonadetes,Spirochaetes,Chlorobi and so on.Proteobacteria is the NO.1 dominant species in all groups,it has the biggest abundance value in rhizosphere of Zizania caduciflora which reach to 50.11%,then 42.12%in Scirpus validus,40.15%in Typha orientalis,39.31%in Phragmites australis,and the smallest in CK whose value is only 24.69%.Firmicutes is the second dormant species,it has the biggest abundance value in CK with 19.86%,then 12.49%,11.42%and 8.25%in Phragmites australis,Typha orientalis and Scirpus validus,and the smallest in Zizania caduciflora with 5.94%.In the Proteobacteria,Betaproteobacteria get the biggest abundance,then the Deltaproteobacteria,Alphaproteobacteria and Gammaproteobacteria.Zizania caduciflora has the most Betaproteobacteria whose abundance value reach 30.90%,CK get the least value with only 7.27%.The Real Time quantitative PCR was used to measure the copy number of total bacterias and functional bacterias involved in nitrogen cycling in the rhizosphere soil of 4 plants.The results reveal that the Typha orientalis get the most rhizosphere bacteria population whose copy number of 16S rDNA is?7.08±0.489?×10⁹·g^-1,then follows the Scirpus validus with copy number?5.34±0.241?×10·g^-1,Phragmites australis and Zizania caduciflora get the least with?1.10±0.498?×10⁹·g^-1 and?1.08±0.0214?×110⁹·g^-1,CK is?9.38±0.285?×108·g^-1.Scirpus validus has the highest nifH with copy number?1.38±0.156?×10⁷·g^-1,Phragmites australis share least with copy number?7.98×0.906?×10⁵·g^-1.According to amoA,Scirpus validus gets the most copy number with?1.83±0.111?×10⁷·g^-1 too,Phragmites australis accounts?1.60±0.229?×10⁶·g^-1 who ranks last.Zizania caduciflora and Typha orientalis have more nirS and nirK than Phragmites australis and Scirpus validus.Zizania caduciflora gets the most copy number of nosZ,it's value is?7.23×1.15?×10⁶·g^-1,but Scirpus validus just gets?2.85±0.735?×10⁶·g^-1.Typha orientalis has amxC copy number with?1.34±0.202?x 10⁶·g^-1,but Phragmites australis and Zizania caduciflora just get?1.27±0.188?xl05·g^-1 and?1.26±0.116?×10⁶·g^-1.We can come to the conclusion that,?1?The dominant species of rhizosphere bacteria of the 4 plants are identical according to phylum and class,while the abundance of each dominant species vary from different groups.?2?Proteobacteria is the NO.1 dominant phylum,and Betaproteobacteria is the most abundance class in all groups.?3?Typha orientalis and Scirpus validus's total number of rhizosphere bacteria are significantly higher than Zizania caduciflora and Phragmites australis,they may have stronger rhizosphere effect.?4?Scirpus validus has a greater number of azotobacters and nitrobacterias so it may has a stronger ability of nitrogen-fixation and nitrification.?5?Typha orientalis and Zizania caduciflora have stronger denitrification ability.?6?Typha orientalis and Scirpus validus has a greater number of anaerobic ammonia oxidation bacteria than Zizania caduciflora and Phragmites australis.?7?Phragmites australis is the weakest one in nitrogen-cycling process compared with another 3 plants.