Isolation And Growth-promoting Effects Of Aaeratina Adenophora Root Endophytic Nitrogen-fixing Bacteria

Invasive plant Ageratina adenophora is one of the most serious weeds in southwest China.At present,the research works on the invasive mechanism of A.adenophora are mainly focused on the feedback of soil microbes.In order to understand the species composition and their growth-promoting effects on A.adenophora,150 root endophytic nitrogen-fixing bacteria(reNFB)from five populations of A.adenophora in invaded regions in Yunnan province,including Ximeng(XM),Cangyuan(CY),Yunlong(YL),Xishan(XS)and Wenshan(WS),were isolated and identified based on their 16S rRNA gene sequences.Their abilities to produce IAA,siderophore,and solubilize phosphate were characterized and their effects on the growth of A.adenophora were also determined.The following main conclusions were made by this experiment:1.Species richness of reNFB in A.adenophora is high.reNFB of A.adenophora included 25 species,such as Agrobacterium tumefaciens,Arthrobacter oxydans,Bacillus sp.,Bosea massiliensis,Brachybernium sp.,Burkholderia sp.,Caulobacter sp.,Devosia riboflavina,Herbaspirillum sp.,Bacillus licheniformis,Lysobacter gummosus,Mitsuaria chitosanitabida,Neorhizobium galegae,Nocardioides albus,Paenibacillus borealis,Pseudomonas sp.,Ralstonia sp.,Rhizobium sp.,and Burkholderia sp.The numerically dominant reNFB are Pseudomonas sp.,Rhizobium sp.and Burkholderia sp.,with the isolation percentage of 55.3%,9.3%and 10.7%,respectively,and accounted for 75.3%of the total isolates.2.reNFB are different in their abilities to produce IAA,siderophore and solubilize phosphate.reNFB collected from different regions had different abilities to produce IAA,siderophore,and solubilize phosphate.All strains could produce IAA,45.3%of these strains had the ability to dissolve the phosphate,and 74.7%of these strains could produce siderophore.From the perspective of the sampling sites,regardless of the incubation time of 72h or 144h,the strains isolated from XM had the strongest but the strains isolated from XS had the weakest ability to produce IAA;the strains isolated from CY had the strongest but the strains isolated from XS had the weakest ability to dissolve phosphate;the strains isolated from CY had the strongest but the strains isolated from XS had the weakest ability to produce siderophore.The ability of the strains isolated from CY to dissolve phosphate and produce siderophore is the strongest.From the perspective of the dominant species,Pseudomonas strains,as a whole,had the strongest ability to produce IAA,dissolve phosphate and produce siderophore,following by Rhizobium to Burkholderia,to a less degree.The strongest ability to produce IAA was isolate XM-1-6(Pseudomonas sp.),with a yield of 40.92 ?g/mL.The strongest ability to dissolve phosphate was isolate CY-2-2(Pseudomonas sp.),with a soluble index of 2.96.The strongest ability to produce siderophore was isolate CY-1-7(Rhizobium sp.),with a siderophore activity unit of 81%.3.The predominant reNFB can promote the growth of A.adenophora.reNFB showed a significant positive effect on growth of A.adenophora,including stem length,root length,aboveground and underground fresh weight,aboveground and underground dry weight.Among of them,isolate XM-1-4(Burkholderia sp.),WS-1-5(Rhizobium sp.)and WS-2-5(Pseudomonas sp.)had statistically significant effects on the stem and root length of A.adenophora.Isolate WS-1-5(Rhizobium sp.)not only promoted the root length,but also promoted the fresh weight and dry weight of A.adenophora.The stem and root length of A.adenophora inoculated with isolate XM-1-4(Burkholderia sp.)were 1.7 and 1.85 times,respectively,of those obtained from the control group.The stem and root length of A.adenophora inoculated with isolate WS-1-5(Rhizobium sp.)were 3.36 and 2.30 times,respectively,of those obtained from the control group.The stem and root length of A.adenophora inoculated with isolate WS-2-5(Pseudomonas sp.)were 2.8 and 2.11 times,respectively,of those obtained from the control group.The aboveground fresh weight and dry weight of A.adenophora inoculated with isolate WS-1-5(Rhizobium sp.)were 37.3 and 2.11 times,respectively,of those obtained from the control group.Isolate XS-3-7(Burkholderia sp.)had a significant effect on the root length,fresh weight,fresh weight and dry weight of A.adenophora,which were 1.79,8.97,25.7 and 31 times,respectively,of those obtained from the control group.In general,reNFB of A.adenophora are capable of producing IAA,siderophore and dissolving phosphate,and are beneficial to the growth of A.adenophora.