Influence Of Alnus Trabeculosa Plantation On The Nitrogen-fixing Bacteria And Ecological Process Of Phragmites Australis In Chongxi Wetland

The effects of introduction of Alnus trabeculosa on nitrogen cycle in Alnustrabeculosa–Phragmites australis mixed communities and P. australis monoculturecommunity in Chongxi wetland were analyzed in this paper. Eight aerobic free livingnitrogen-fixing bacteria were isolated from the rhizosphere and non-rhizosphere ofdifferent plant communities. On the basis of acetylene reduction activity and theamplification of16S rDNA and nifH gene, two kinds of phylogenetic trees wereconstructed to analyse the strains isolated. Using real-time PCR, we investigatedfunctional gene abundances of bacteria and archaea performing nitrogen fixation,nitrification and denitrification for subunits of the nitrogenase (nifH), the ammoniamonooxygenase (amoA), and the nitrous oxide reductase (nosZ). The main results aresummarized as follows:1) After the introduction of A.trabeculosa, the content of organic matter, totalnitrogen, nitrate nitrogen and ammoniacal nitrogen had risen significantly, and theeffects on physicochemical property of rhizosphere soils in P.australis communitywere more than non-rhizosphere ones.2) The number of culturable nitrogen-fixing microorganism in the rhizosphere ofA.trabeculosa was the highest, while the rhizosphere in P.australis has the lowest one.3) On the basis of acetylene reduction activity, Strain MAR-1had the highestactivity (261.3nmol/mL·h)(P<0.01).4) According to the phylogenetic analysis of16Sr DNA and nifH sequences, these8isolates had high similarity, and clusters were nearly all clustered together withPseudomonas. Sp. They were identifed as novel nitrogen-fixing bacteria. Thephylogenetic analysis of16Sr DNA and nifH sequences had a good consistency.5) As nifH, nosZ, AOA and AOB amoA genes turned out to be highly abundant inthe rhizosphere and non-rhizosphere of different plant communities.6) AOA is dominant in the process of ammoxidation of P.australis community inthis study. The introduction of A.trabeculosa led to lower abundance of nifH andAOA amoA gene copies in the non-rhizosphere than rhizosphere, no differences in AOB community composition, and lower abundance of nosZ gene copies betweenrhizosphere and non-rhizosphere in P.australis community.7) The nifH gene is the dominant function gene of nitrogen transformation in thisstudy, and the nitrogen fixing bacteria were distributed in various ecosystems andprevalent in different plant communities.